Thoracic Anatomy

1. Quick Answer

Thoracic anatomy encompasses the bony thoracic cage, intercostal spaces, pleura, mediastinum, lungs, diaphragm, great vessels, and thoracic duct - the structures contained within and forming the thorax from the thoracic inlet superiorly to the diaphragm inferiorly.

Key Concepts:

• The thoracic cage comprises 12 pairs of ribs, thoracic vertebrae, and sternum, providing protection for vital organs while allowing respiratory movement
• The intercostal neurovascular bundle runs in the subcostal groove in VAN order (Vein-Artery-Nerve from superior to inferior)
• Pleura (visceral and parietal layers) create a potential space maintained at subatmospheric pressure, essential for lung expansion
• The mediastinum contains the heart, great vessels, trachea, oesophagus, and thoracic duct

ICU Relevance:

• Critical for chest drain insertion (triangle of safety: 4th-5th ICS, mid-axillary line)
• Understanding surface anatomy essential for thoracentesis, pericardiocentesis, and thoracotomy
• Central venous access requires knowledge of great vessel anatomy
• Lung isolation for single-lung ventilation requires bronchopulmonary segment understanding

Exam Focus:

• CICM First Part examiners commonly ask about intercostal neurovascular anatomy, pleural surface markings, mediastinal contents, and applied anatomy for ICU procedures

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2. CICM First Part Exam Focus

What Examiners Expect

Written SAQ:

Common question stems:

• "Describe the anatomy of the intercostal space with particular reference to the neurovascular bundle and its clinical significance" (10 marks)
• "Draw and label a cross-section of the thorax at the level of T8" (8 marks)
• "Describe the anatomy of the pleura including surface markings and pleural recesses" (10 marks)
• "Outline the contents of the mediastinum with their anatomical relationships" (12 marks)
• "Describe the anatomy of the diaphragm including its openings and innervation" (10 marks)
• "Describe the surface anatomy relevant to chest drain insertion" (8 marks)

Expected depth:

• Detailed anatomical knowledge with named structures and spatial relationships
• Accurate surface anatomy with vertebral and rib levels
• Clear diagrams with accurate labeling showing layers and structures
• Explicit ICU application (chest drains, thoracentesis, thoracotomy, lung isolation)
• Integration with clinical procedures and potential complications

Written MCQ:

Common topics tested:

• Intercostal neurovascular bundle order and position
• Rib classification (true, false, floating)
• Pleural recesses and their clinical significance
• Mediastinal divisions and contents
• Diaphragm openings and vertebral levels
• Surface anatomy landmarks for procedures
• Bronchopulmonary segment nomenclature

Difficulty level:

• Applied anatomical scenarios (e.g., "During chest drain insertion, which structure is at greatest risk of injury?")
• Identification of structures from cross-sectional descriptions
• Clinical consequences of anatomical injury

Oral Viva:

Expected discussion flow:

1. Define/Describe - Overview of thoracic boundaries and contents
2. Thoracic Cage - Ribs, sternum, thoracic vertebrae, joints
3. Intercostal Space - Layers, neurovascular bundle, clinical application
4. Pleura - Divisions, recesses, surface markings
5. Mediastinum - Divisions and contents
6. Lungs - Lobes, fissures, bronchopulmonary segments
7. Diaphragm - Structure, openings, innervation
8. Applied Anatomy - Chest drain, thoracentesis, pericardiocentesis, thoracotomy

Common viva scenarios:

• "Walk me through the layers you would traverse during chest drain insertion"
• "A patient requires thoracentesis. Describe the surface anatomy and safe approach"
• "Describe the anatomy of the mediastinum relevant to central line insertion"

Pass vs Fail Performance

Pass Standard:

• Accurate description of intercostal space anatomy with VAN bundle
• Correct identification of pleural recesses and surface markings
• Clear understanding of mediastinal divisions and key contents
• Knowledge of diaphragm openings and their vertebral levels
• Ability to describe surface landmarks for common ICU procedures
• Draws clear diagrams of thoracic structures and cross-sections

Common Reasons for Failure:

• Confusing the order of intercostal neurovascular bundle
• Incorrect pleural surface markings (especially the oblique fissure)
• Not knowing the contents of each mediastinal division
• Confusion between costophrenic and costomediastinal recesses
• Unable to describe safe zone for chest drain insertion
• Poor understanding of diaphragm innervation (phrenic nerve C3-5)

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3. Key Points

10 Must-Know Facts

1. Intercostal Neurovascular Bundle: The intercostal vein, artery, and nerve (VAN) run in the subcostal groove along the inferior border of each rib from superior to inferior. Chest drains should be inserted just ABOVE the rib to avoid injury (PMID: 20456826).

2. Triangle of Safety (Safe Zone): For chest drain insertion, bounded by anterior border of latissimus dorsi, lateral border of pectoralis major, horizontal line at nipple level (5th intercostal space), and apex at axilla. The 4th-5th intercostal space in the mid-axillary line is the standard insertion point (PMID: 20456826).

3. Pleural Surface Markings: Lung apex extends 2.5 cm above medial third of clavicle; costodiaphragmatic recess (costophrenic angle) at rib 8 (MCL), rib 10 (MAL), rib 12 (posteriorly). Lung does not extend into the recess in normal respiration (PMID: 15833165).

4. Diaphragm Openings: IVC at T8 (in central tendon, with right phrenic nerve), oesophagus at T10 (in muscular part, with vagus nerves and oesophageal vessels), aorta at T12 (behind median arcuate ligament, with azygos vein and thoracic duct) (PMID: 22585726).

5. Phrenic Nerve (C3, C4, C5): "C3, 4, 5 keeps the diaphragm alive"

• sole motor supply to diaphragm; injury causes hemidiaphragm paralysis with 25% reduction in vital capacity. Passes anterior to lung root (PMID: 24852527).

6. Mediastinum Divisions: Superior (above sternal angle/T4-5) and inferior mediastinum divided into anterior (thymus), middle (heart, pericardium, great vessels), and posterior (oesophagus, descending aorta, thoracic duct, azygos system) (PMID: 31482108).

7. Bronchopulmonary Segments: Right lung has 10 segments (3 upper, 2 middle, 5 lower); left lung has 8-10 segments (4-5 upper including lingula, 4-5 lower). Each segment is surgically resectable as independent broncho-vascular unit (PMID: 12167576).

8. Thoracic Duct: Largest lymphatic vessel, originates from cisterna chyli at L2, enters thorax through aortic hiatus at T12, crosses from right to left at T5, drains into junction of left internal jugular and subclavian veins. Drains 75% of body lymph (PMID: 25073584).

9. Intercostal Nerve Dermatomes: T4 at nipple level, T10 at umbilicus, T6 at xiphisternum. Essential for assessing epidural level and intercostal blocks (PMID: 26891953).

10. Right Main Bronchus Anatomy: Shorter (2.5 cm), wider, and more vertical (25° from midline) than left; more common site for aspiration and endobronchial intubation. Right upper lobe bronchus arises 2.5 cm from carina (PMID: 12167576).

Essential Anatomical Relationships

Thoracic Inlet (Superior Thoracic Aperture):

• Bounded by: T1 vertebra, 1st ribs, manubrium
• Contents: Apex of lungs and pleura, subclavian vessels, brachial plexus, trachea, oesophagus, thoracic duct, sympathetic chain
• Clinical significance: Pancoast tumour, thoracic outlet syndrome, supraclavicular approach to subclavian vein

Sternal Angle (Angle of Louis):

• Level of T4-5 vertebral body
• Landmark for: 2nd costal cartilage, bifurcation of trachea, aortic arch begins/ends, superior mediastinum boundary

Normal Values Table

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4. Thoracic Cage

4.1 Ribs

The thorax contains 12 pairs of ribs, classified based on their anterior attachment:

Classification

True Ribs (1-7): Attach directly to sternum via costal cartilages

• Rib 1: Shortest, most curved, broadest; single costal groove; articulates with T1 only
• Rib 2: Has tuberosity for serratus anterior attachment
• Ribs 3-7: Typical ribs with head, neck, tubercle, and body

False Ribs (8-10): Attach indirectly to sternum via cartilage of rib above

• Share common costochondral junction forming costal margin

Floating Ribs (11-12): No anterior attachment

• Short, with no tubercle and rudimentary costal groove
• End in abdominal musculature

Typical Rib Anatomy (Ribs 3-9)

A typical rib has the following components [1]:

Head: Two articular facets separated by crest

• Superior facet: Articulates with vertebra above (numerically same as rib)
• Inferior facet: Articulates with vertebra of same number
• Crest: Attachment of intra-articular ligament

Neck: Flattened portion connecting head to tubercle

• Anterior surface: Smooth
• Posterior surface: Roughened for costotransverse ligament

Tubercle: Projection at junction of neck and shaft

• Articular part: Facet for transverse process of corresponding vertebra
• Non-articular part: Attachment for costotransverse ligament

Shaft (Body): Curved, flattened bone

• External surface: Convex with angle (posterior angulation)
• Internal surface: Concave with subcostal groove for neurovascular bundle
• Superior border: Rounded
• Inferior border: Sharp, with subcostal groove

Subcostal Groove: Contains (from superior to inferior):

• Intercostal vein (most superior)
• Intercostal artery (middle)
• Intercostal nerve (most inferior)
• Mnemonic: VAN (Vein-Artery-Nerve, superior to inferior)

Atypical Ribs

Rib 1 [2]:

• Short, broad, flat (horizontal orientation)
• Single articular facet on head (T1 only)
• Two grooves on superior surface for subclavian vessels
• Scalene tubercle between grooves (scalenus anterior insertion)
• No subcostal groove

Rib 2:

• Tuberosity for serratus anterior on external surface
• Less curved than rib 1

Rib 10: Single articular facet (T10 only)

Ribs 11-12:

• Single articular facet
• No tubercle (no articulation with transverse process)
• Short, pointed
• Rudimentary or absent subcostal groove

4.2 Sternum

The sternum is a flat bone forming the anterior midline of the thoracic cage [3].

Parts of the Sternum

Manubrium:

• Superior portion, approximately 4 cm long
• Jugular (suprasternal) notch at superior border
• Clavicular notches at superolateral angles
• Costal notch for 1st rib laterally
• Demifacet for 2nd rib inferolaterally

Body (Gladiolus):

• Longest portion, approximately 10 cm
• Fused from 4 sternebrae
• Costal notches for ribs 2-7 along lateral borders

Xiphoid Process:

• Smallest portion, variable in shape (may be bifid or perforated)
• Cartilaginous until approximately 40 years of age
• Landmark for subxiphoid pericardiocentesis

Sternal Angle (Angle of Louis)

The junction between manubrium and body creates a palpable transverse ridge:

• Level of T4-5 vertebral body
• Attachment of 2nd costal cartilage (palpable landmark for rib counting)
• Marks: Aortic arch beginning/ending, tracheal bifurcation, superior mediastinum lower boundary

Joints

Sternoclavicular Joint: Synovial joint with articular disc Manubriosternal Joint (Sternal Angle): Symphysis or synchondrosis Xiphisternal Joint: Synchondrosis (may ossify with age) Sternocostal Joints: 1st is synchondrosis; 2nd-7th are synovial (allow respiratory movement)

4.3 Thoracic Vertebrae

The 12 thoracic vertebrae have distinctive features [4]:

Typical Features (T2-T9)

Body: Heart-shaped, size increases from T1 to T12

• Superior and inferior costal demifacets for rib head articulation

Pedicles: Project posterolaterally

Transverse Processes: Project laterally and posteriorly

• Costal facet for articulation with rib tubercle (absent T11-12)

Spinous Process: Long, sloping inferiorly, overlapping

Vertebral Foramen: Smaller and more circular than cervical/lumbar

Superior Articular Facets: Face posterolaterally

Inferior Articular Facets: Face anteromedially

Atypical Features

T1: Resembles C7; complete superior costal facet, demifacet inferiorly T9: May lack inferior demifacet T10: Single complete costal facet on body T11-12: Complete costal facets, no transverse process costal facets

4.4 Intercostal Spaces

There are 11 intercostal spaces, numbered by the rib above.

Clinical Significance [5]

Intercostal Drain Insertion:

• Triangle of safety: 4th-5th ICS, anterior to mid-axillary line
• Insert just above rib to avoid neurovascular bundle
• Avoid posterior triangle (scapula)

Thoracentesis:

• Target: 8th-9th ICS, posterior axillary line
• Below tip of scapula (rib 7 posteriorly)
• Ultrasound guidance reduces complication rate by 19% (PMID: 20456826)

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5. Intercostal Space

The intercostal space is the region between adjacent ribs, containing muscles, vessels, and nerves essential for respiratory mechanics and clinical procedures [6].

5.1 Boundaries

Superior: Lower border of rib above Inferior: Upper border of rib below Anterior: Sternum and costal cartilages Posterior: Thoracic vertebral bodies and transverse processes External: Skin and superficial fascia Internal: Endothoracic fascia and parietal pleura

5.2 Layers (Superficial to Deep)

From superficial to deep, the intercostal space contains:

1. Skin
2. Superficial fascia
3. Deep fascia
4. External intercostal muscle
5. Internal intercostal muscle
6. Innermost intercostal muscle
7. Endothoracic fascia
8. Parietal pleura

5.3 Intercostal Muscles

External Intercostal Muscle

Origin: Lower border of rib above Insertion: Upper border of rib below Fibre Direction: Obliquely downward and forward ("hands in pockets") Extent: From tubercle of rib posteriorly to costochondral junction anteriorly

• Anteriorly continues as external intercostal membrane

Action: Elevates ribs during inspiration Innervation: Intercostal nerves

Internal Intercostal Muscle

Origin: Floor of subcostal groove and costal cartilage Insertion: Upper border of rib below Fibre Direction: Obliquely downward and backward (perpendicular to external intercostals) Extent: From sternum anteriorly to angle of rib posteriorly

• Posteriorly continues as internal intercostal membrane

Action: Depresses ribs during forced expiration (interchondral portion may be inspiratory) Innervation: Intercostal nerves

Innermost Intercostal Muscle

Origin: Internal aspect of rib Insertion: Internal aspect of adjacent rib (1-2 ribs below) Fibre Direction: Similar to internal intercostal Extent: Limited to lateral portion of intercostal space

Components: Three muscle groups with similar innervation and function:

• Transversus thoracis (sternocostalis): Anterior, deep to sternum
• Innermost intercostal: Lateral portion
• Subcostalis: Posterior, crosses multiple ribs

Significance: The neurovascular bundle runs between internal and innermost intercostal muscles

5.4 Intercostal Neurovascular Bundle

The intercostal neurovascular bundle runs in the subcostal groove along the inferior border of each rib [7].

Components (Superior to Inferior)

Mnemonic: VAN (Vein-Artery-Nerve)

1. Intercostal Vein (most superior)
2. Intercostal Artery (middle)
3. Intercostal Nerve (most inferior)

Position

• Runs between internal and innermost intercostal muscles
• Protected by subcostal groove of rib above
• Collateral branches run along superior border of rib below

Clinical Significance

Chest Drain Insertion:

• Insert needle/trocar just ABOVE the rib (not below)
• Avoids neurovascular bundle in subcostal groove
• Ensures entry above main bundle while avoiding collaterals

Nerve Block:

• Target posterior angle of rib for intercostal nerve block
• Local anaesthetic deposited deep to internal intercostal muscle

5.5 Intercostal Arteries

Posterior Intercostal Arteries [8]

Spaces 1-2: From supreme intercostal artery (costocervical trunk of subclavian) Spaces 3-11: From descending thoracic aorta

• Right arteries longer, cross vertebral bodies behind oesophagus, thoracic duct, and azygos vein

Course:

• Enter intercostal space between internal and innermost intercostal muscles
• Run with intercostal vein (above) and nerve (below)
• Divide into:
  • "Lateral cutaneous branch: Pierces with lateral cutaneous nerve"
  • "Collateral branch: Runs along superior border of rib below"
  • "Terminal branch: Continues to anastomose with anterior intercostal artery"

Anterior Intercostal Arteries

Spaces 1-6: From internal thoracic artery Spaces 7-9: From musculophrenic artery (terminal branch of internal thoracic)

Course: Two small branches per space, running on upper and lower borders of intercostal space

Subcostal Arteries

Run below rib 12, from descending aorta

5.6 Intercostal Veins

Follow the corresponding arteries but drain differently:

Posterior Intercostal Veins:

• Right: Spaces 2-4 to superior intercostal vein → azygos vein
  • Space 1 may drain directly to brachiocephalic vein
  • Spaces 5-11 directly to azygos vein
• Left: Spaces 2-4 to superior intercostal vein → left brachiocephalic vein
  • Space 1 to left brachiocephalic vein directly
  • Spaces 4-8 may drain to accessory hemiazygos
  • Spaces 9-11 to hemiazygos vein

Anterior Intercostal Veins: Drain to internal thoracic veins

5.7 Intercostal Nerves

The intercostal nerves are the ventral rami of thoracic spinal nerves T1-T11 [9].

Course

1. Exit intervertebral foramen
2. Enter intercostal space between parietal pleura and internal intercostal membrane
3. Run in subcostal groove between internal and innermost intercostal muscles
4. Give branches and continue as anterior cutaneous nerve

Branches

Collateral Branch: Runs along upper border of rib below (motor to intercostal muscles)

Lateral Cutaneous Branch: Emerges at mid-axillary line, divides into anterior and posterior branches

• T2 is intercostobrachial nerve (supplies medial arm, axilla)

Anterior Cutaneous Branch: Terminal branch, emerges near midline

Muscular Branches: To intercostal and accessory respiratory muscles

Dermatomes

Clinical Application

Epidural Anaesthesia Level Assessment:

• T4 (nipple) for thoracic surgery
• T6-T10 for abdominal surgery
• Assess using cold spray or pinprick

Intercostal Nerve Block:

• Target posterior angle of rib
• Inject deep to internal intercostal muscle
• Provides analgesia for rib fractures, chest wall procedures

5.8 Atypical Intercostal Nerves

T1: Majority joins C8 to form lower trunk of brachial plexus; small intercostal component

T2 (Intercostobrachial Nerve): Large lateral cutaneous branch crosses axilla to supply medial arm; may communicate with medial cutaneous nerve of arm

T7-T11: Continue beyond costal margin as thoracoabdominal nerves, supplying anterior abdominal wall

Subcostal Nerve (T12): Below rib 12, supplies abdominal wall to pubic symphysis

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6. Pleura

The pleura is a serous membrane lining the thoracic cavity and covering the lungs [10,11].

6.1 Parietal Pleura

Lines the inner surface of the thoracic wall, mediastinum, and diaphragm.

Divisions

Costal Pleura:

• Lines inner aspect of ribs, intercostal muscles, and thoracic vertebrae
• Separated from thoracic wall by endothoracic fascia
• During thoracentesis/chest drain insertion, parietal pleura is punctured

Mediastinal Pleura:

• Covers lateral aspect of mediastinum
• Reflected onto lung root as pulmonary ligament (below lung root)
• Contains phrenic nerve and pericardiophrenic vessels between fibrous pericardium and mediastinal pleura

Diaphragmatic Pleura:

• Covers superior surface of diaphragm (except central tendon where pericardium attaches)
• Separated from diaphragmatic muscle by endothoracic fascia
• Supplied by intercostal nerves peripherally and phrenic nerve centrally

Cervical Pleura (Pleural Cupola/Dome):

• Extends 2.5 cm above medial third of clavicle
• Protected by Sibson's fascia (suprapleural membrane)
• Clinical significance: Risk of pneumothorax during subclavian vein cannulation and brachial plexus block

Innervation of Parietal Pleura

• Costal pleura: Intercostal nerves (T1-T11) - localizable pain
• Diaphragmatic pleura: Peripheral (intercostal nerves) - localizable pain; Central (phrenic nerve) - referred to shoulder (C3-5)
• Mediastinal pleura: Phrenic nerve

6.2 Visceral Pleura

Intimately covers lung surface, extending into fissures.

Characteristics

• Continuous with parietal pleura at lung root
• Cannot be separated from underlying lung parenchyma
• Contains lymphatics draining toward lung hilum
• Innervated by autonomic nerves (insensitive to pain)

6.3 Pleural Cavity

Definition: Potential space between visceral and parietal pleura

Contents:

• Normal: 5-15 mL serous fluid (lubricant)
• Pathological: Blood (haemothorax), air (pneumothorax), pus (empyema), lymph (chylothorax), transudate, exudate

Pressure:

• Normally subatmospheric (-3 to -5 cmH₂O at FRC)
• More negative at apex (due to gravity)
• Essential for lung expansion during inspiration

6.4 Pleural Recesses

Potential spaces where parietal pleura reflects on itself, not occupied by lung in normal quiet breathing [12].

Costodiaphragmatic Recess

Location: Between costal and diaphragmatic pleura Clinical Significance: Largest recess; first site of pleural effusion accumulation; target for thoracentesis

Extent (Lower Limit of Parietal Pleura):

• Midclavicular line: Rib 8
• Mid-axillary line: Rib 10
• Posterior (scapular line): Rib 12

Lung Margin (Lower Limit of Lung):

• Midclavicular line: Rib 6
• Mid-axillary line: Rib 8
• Posterior: Rib 10

Gap: 2 ribs between lung and pleural margin (recess)

Costomediastinal Recess

Location: Between costal and mediastinal pleura, behind sternum Right: Minimal gap (ribs 2-4) Left: Larger due to cardiac notch (ribs 4-6) - accessed for pericardiocentesis without crossing pleura

6.5 Surface Anatomy of Pleura

Superior Extent (Pleural Apex)

• 2.5 cm above medial third of clavicle
• Level with neck of 1st rib
• Protected by suprapleural membrane (Sibson's fascia)

Anterior Borders

Right Pleura:

• From behind sternoclavicular joint
• Descends behind manubrium to midline at sternal angle
• Continues vertically to xiphisternal joint
• Curves laterally to reach rib 6 at midclavicular line

Left Pleura:

• Similar to right to level of 4th costal cartilage
• Deviates laterally (cardiac notch) to 6th costal cartilage
• At MCL, level with rib 6

Posterior Borders

• Both sides: From pleural apex, descend along vertebral column
• Lateral to vertebral bodies, crossing transverse processes

Inferior Borders (Costodiaphragmatic Line)

Mnemonic: "8, 10, 12" (ascending rib numbers from front to back)

6.6 Blood Supply

Parietal Pleura: Intercostal arteries, internal thoracic artery, musculophrenic artery

Visceral Pleura: Bronchial arteries

6.7 Lymphatic Drainage

Parietal Pleura: To intercostal, internal thoracic, posterior mediastinal, and diaphragmatic nodes

Visceral Pleura: To bronchopulmonary and tracheobronchial nodes

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7. Mediastinum

The mediastinum is the central compartment of the thorax between the two pleural cavities [13,14].

7.1 Boundaries

Superior: Thoracic inlet (plane from superior border of manubrium to T1 vertebra) Inferior: Diaphragm Anterior: Sternum and costal cartilages Posterior: Thoracic vertebrae (T1-T12) Lateral: Mediastinal pleura bilaterally

7.2 Divisions

The mediastinum is divided by an imaginary plane through the sternal angle and T4-T5 disc:

Superior Mediastinum

Boundaries:

• Superior: Thoracic inlet
• Inferior: Plane through sternal angle to T4-T5
• Anterior: Manubrium
• Posterior: Bodies of T1-T4 vertebrae

Contents (Anterior to Posterior):

1. Thymus (or remnant)
2. Great vessels:
   • Aortic arch and branches (brachiocephalic, left common carotid, left subclavian)
   • Superior vena cava (formed by brachiocephalic veins)
3. Trachea
4. Oesophagus (posterior to trachea)
5. Thoracic duct (on left of oesophagus)
6. Nerves:
   • Vagus nerves
   • Left recurrent laryngeal nerve (loops under aortic arch)
   • Phrenic nerves (pass anterior to lung roots)
7. Lymph nodes: Paratracheal

Inferior Mediastinum

Divided into anterior, middle, and posterior compartments.

Anterior Mediastinum

Location: Between sternum and pericardium Contents:

• Thymic remnants (if persisting beyond superior mediastinum)
• Fat
• Lymph nodes (internal thoracic/parasternal)
• Internal thoracic vessels (superior portion)

Middle Mediastinum

Location: Contains pericardium and its contents Contents:

1. Pericardium (fibrous and serous)
2. Heart and great vessel roots
3. Ascending aorta (origin to aortic arch)
4. Pulmonary trunk (bifurcating into pulmonary arteries)
5. Superior vena cava (lower portion)
6. Pulmonary veins (entering left atrium)
7. Main bronchi
8. Phrenic nerves (on lateral pericardium with pericardiophrenic vessels)
9. Bifurcation of trachea (carina at T4-T5)
10. Tracheobronchial lymph nodes

Posterior Mediastinum

Location: Between pericardium anteriorly and vertebral column posteriorly

Contents:

1. Oesophagus (descending from superior mediastinum to pass through diaphragm at T10)
2. Descending thoracic aorta (from T4 to T12)
3. Thoracic duct (enters at T12, crosses to left at T5, ascends to neck)
4. Azygos venous system:
   • Azygos vein (right)
   • Hemiazygos vein (left, lower)
   • Accessory hemiazygos vein (left, upper)
5. Vagus nerves (form oesophageal plexus)
6. Splanchnic nerves (greater, lesser, least - pass to abdomen)
7. Sympathetic chains (on vertebral bodies, posterior to pleura)
8. Posterior intercostal vessels (proximal portions)
9. Lymph nodes: Posterior mediastinal

7.3 Key Anatomical Relationships

Trachea

• Anterior: Thyroid isthmus (overlies rings 2-4), brachiocephalic artery (right), left common carotid (left)
• Posterior: Oesophagus (with recurrent laryngeal nerves in tracheo-oesophageal groove)
• Lateral: Lobes of thyroid, common carotid arteries, vagus nerves

Oesophagus

• Anterior: Trachea (superior), left main bronchus and left atrium (inferior)
• Posterior: Vertebral bodies, thoracic duct, azygos vein
• Left: Aortic arch, descending thoracic aorta, thoracic duct
• Right: Azygos vein (arches over right main bronchus to enter SVC)

Aortic Arch

Branches (Right to Left): Brachiocephalic trunk → Right common carotid + Right subclavian, Left common carotid, Left subclavian

Relations:

• Anterior and to left: Phrenic and vagus nerves, left lung and pleura
• Posterior: Trachea (bifurcation), oesophagus, thoracic duct, deep cardiac plexus
• Inferior: Pulmonary trunk bifurcation, left main bronchus, ligamentum arteriosum, left recurrent laryngeal nerve

7.4 Clinical Correlations

Mediastinal Masses by Compartment:

Central Line Insertion:

• Internal jugular approach: Needle passes lateral to common carotid, enters SVC
• Subclavian approach: Risk to subclavian artery, brachial plexus, thoracic duct (left side), pleural dome

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8. Lungs

8.1 External Anatomy

The lungs are paired organs of respiration occupying most of the thoracic cavity [15,16].

Surfaces

Costal Surface: Convex, against ribs and intercostal spaces; impressions from ribs visible

Mediastinal (Medial) Surface: Concave; contains hilum and impressions from mediastinal structures

Diaphragmatic Surface (Base): Concave, rests on diaphragm; right side higher (liver)

Apex: Rises 2.5 cm above clavicle into neck; grooved by subclavian artery

Borders

Anterior Border: Sharp; right border nearly vertical; left border has cardiac notch (between ribs 4-6)

Posterior Border: Broad, rounded; occupies paravertebral gutter

Inferior Border: Sharp, separates base from costal surface; descends into costodiaphragmatic recess during deep inspiration

8.2 Lobes and Fissures

Right Lung

Lobes: Superior, middle, inferior (3 lobes)

Fissures:

• Oblique fissure: Separates inferior lobe from superior and middle lobes
  • "Surface marking: From T3 spinous process, around chest to 6th costal cartilage anteriorly"
  • Follows medial border of scapula with arm raised
• Horizontal fissure: Separates superior from middle lobe
  • "Surface marking: Runs horizontally from oblique fissure at mid-axillary line to 4th costal cartilage"

Left Lung

Lobes: Superior (with lingula), inferior (2 lobes)

Fissures:

• Oblique fissure: Only fissure; separates superior from inferior lobe
  • Similar surface marking to right oblique fissure
• No horizontal fissure
• Lingula: Tongue-like projection of superior lobe, homologous to right middle lobe

8.3 Hilum (Root of Lung)

The hilum is the medial aspect where structures enter and exit the lung [17].

Contents (From Anterior to Posterior)

Mnemonic: "RALS" (Pulmonary veins anterior, then arteries, bronchi, lymphatics posterior)

Bronchus: Posterior

• Right: Eparterial bronchus (above pulmonary artery)
• Left: Below pulmonary artery (hyparterial)

Pulmonary Artery: Middle

• Right: Enters hilum posterior to SVC
• Left: Anterior and superior to bronchus, arches over left main bronchus

Pulmonary Veins: Anterior and inferior

• Two veins (superior and inferior) from each lung
• Enter left atrium

Bronchial Vessels: Posterior

Lymphatics and Nodes: Hilar (bronchopulmonary) nodes

Pulmonary Ligament: Inferior extension of mediastinal pleura below hilum

8.4 Bronchopulmonary Segments

Each lung is divided into bronchopulmonary segments - the largest subdivisions of lobes [18].

Characteristics

• Pyramidal in shape with apex toward hilum
• Supplied by tertiary (segmental) bronchus
• Supplied by branch of pulmonary artery
• Drained by pulmonary veins at periphery (intersegmental)
• Surgically resectable (segmentectomy)

Right Lung Segments (10 segments)

Upper Lobe (3 segments):

1. Apical
2. Posterior
3. Anterior

Middle Lobe (2 segments): 4. Lateral 5. Medial

Lower Lobe (5 segments): 6. Superior (apical) 7. Medial basal 8. Anterior basal 9. Lateral basal 10. Posterior basal

Left Lung Segments (8-10 segments)

Upper Lobe (4-5 segments):

1. Apicoposterior (combined in left lung)
2. Anterior
3. Superior lingular
4. Inferior lingular

Lower Lobe (4-5 segments): 5. Superior (apical) 6. Anteromedial basal (combined in left lung) 7. Lateral basal 8. Posterior basal

8.5 Surface Anatomy of Lungs

Lung Borders

Apex: 2.5 cm above medial third of clavicle

Anterior Border:

• Right: Behind sternoclavicular joint, descends vertically to 6th costal cartilage at MCL
• Left: Similar to right until 4th costal cartilage, then cardiac notch deviates laterally, reaches 6th costal cartilage lateral to MCL

Lower Border:

• Midclavicular line: Rib 6
• Mid-axillary line: Rib 8
• Scapular line: Rib 10

Mnemonic: "6, 8, 10" for lung borders (2 ribs higher than pleural borders)

Fissure Surface Markings

Oblique Fissure (Both Lungs):

• Begins at T3 spinous process (or 3rd thoracic spine)
• Follows medial border of scapula (arm raised)
• Crosses 5th rib at mid-axillary line
• Ends at 6th costal cartilage anteriorly

Horizontal Fissure (Right Lung Only):

• From oblique fissure at mid-axillary line (approximately 5th rib)
• Runs horizontally to 4th costal cartilage at anterior chest

8.6 Blood Supply

Pulmonary Circulation (Gas Exchange)

Pulmonary Arteries: Carry deoxygenated blood from right ventricle

• Right pulmonary artery: Longer, passes behind ascending aorta and SVC
• Left pulmonary artery: Shorter, passes anterior to descending aorta

Pulmonary Veins: Return oxygenated blood to left atrium

• Two from each lung (superior and inferior)
• No valves

Bronchial Circulation (Nutritive)

Bronchial Arteries:

• Left (2): Usually from thoracic aorta directly
• Right (1): Usually from 3rd posterior intercostal artery or aorta

Bronchial Veins: Drain to azygos system (right) and accessory hemiazygos or left superior intercostal vein (left)

Note: Bronchopulmonary anastomoses contribute to physiological shunt

8.7 Nerve Supply

Parasympathetic: Vagus nerve

• Bronchoconstriction
• Increased glandular secretion

Sympathetic: T2-T5 via pulmonary plexus

• Bronchodilation
• Decreased secretion

Pulmonary Plexus: Anterior and posterior; formed by vagal and sympathetic fibres around pulmonary arteries at hilum

8.8 Lymphatic Drainage

Superficial (Subpleural): Drains towards hilum and posterior mediastinum

Deep (Peribronchial and Perivascular): Drains to bronchopulmonary (hilar) nodes → tracheobronchial nodes → paratracheal nodes → bronchomediastinal trunk

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9. Diaphragm

The diaphragm is the primary muscle of respiration, separating the thoracic and abdominal cavities [19,20].

9.1 Structure

Shape: Dome-shaped musculotendinous septum

Central Tendon: Trefoil-shaped (three-leafed clover) aponeurosis

• Does not attach to vertebral column (allows oesophageal and IVC passages)
• Fused with fibrous pericardium above

Muscle Fibres: Radiate from central tendon to peripheral attachments

9.2 Origin (Peripheral Attachments)

The diaphragm originates from three groups of fibres:

Sternal Part

• Origin: Posterior surface of xiphoid process
• Fibres: Two small slips

Costal Part

• Origin: Inner surfaces of lower 6 costal cartilages (7-12) and ribs
• Interdigitates with transversus abdominis muscle
• Largest portion

Vertebral Part (Crura and Arcuate Ligaments)

Right Crus:

• Origin: Bodies of L1, L2, L3 vertebrae and intervertebral discs
• Larger and longer than left
• Some fibres loop around oesophagus (forming oesophageal sphincter)

Left Crus:

• Origin: Bodies of L1, L2 vertebrae and disc

Arcuate Ligaments (Lumbocostal Arches):

9.3 Insertion

All fibres converge on the central tendon (also called centrum tendineum)

9.4 Diaphragmatic Openings

Three major openings allow passage of structures between thorax and abdomen [21].

Caval Opening (T8)

Level: T8 vertebral level (highest opening) Location: In the central tendon (right leaf) Contents:

• Inferior vena cava
• Right phrenic nerve (or branches)
• Lymphatics from liver

Clinical Note: In central tendon, so IVC does not constrict during diaphragmatic contraction (maintains venous return)

Oesophageal Hiatus (T10)

Level: T10 vertebral level Location: In the muscular part, formed by right crus fibres Contents:

• Oesophagus
• Anterior and posterior vagal trunks
• Oesophageal branches of left gastric vessels
• Lymphatics

Clinical Note: In muscular part, so constricts during contraction (helps prevent reflux); site of hiatus hernia

Aortic Hiatus (T12)

Level: T12 vertebral level (lowest opening) Location: Behind diaphragm (not through it), between crura and posterior to median arcuate ligament Contents:

• Aorta (becomes abdominal aorta)
• Thoracic duct
• Azygos vein (sometimes)

Clinical Note: Aorta passes BEHIND diaphragm, so not compressed during contraction; pulsation maintained

Mnemonic for Vertebral Levels: "I 8 (ate) 10 Eggs At 12" = IVC at T8, Oesophagus at T10, Aorta at T12

9.5 Other Structures Passing Through/Around Diaphragm

9.6 Innervation

Motor Supply: Phrenic nerve (C3, C4, C5) - SOLE motor supply

Mnemonic: "C3, 4, 5 keeps the diaphragm alive"

Course of Phrenic Nerve:

• Arises from cervical plexus
• Descends through neck on scalenus anterior
• Enters thorax between subclavian artery and vein
• Descends anterior to lung root on pericardium (with pericardiophrenic vessels)
• Right: Shorter, more vertical; pierces diaphragm at caval opening
• Left: Longer, crosses aortic arch; pierces muscular portion of diaphragm

Sensory Supply:

• Central diaphragm: Phrenic nerve (C3-5) → referred pain to shoulder tip (C3-5 dermatome)
• Peripheral diaphragm: Intercostal nerves (T7-T12) → referred pain to lower chest wall and abdominal wall

9.7 Blood Supply

Arterial:

• Superior phrenic arteries (from thoracic aorta)
• Inferior phrenic arteries (from abdominal aorta - major supply)
• Musculophrenic arteries (from internal thoracic)
• Pericardiophrenic arteries (from internal thoracic)

Venous: Drain to inferior phrenic veins → IVC; also to azygos system

9.8 Actions and Mechanics

Contraction:

• Descends 1-2 cm during quiet breathing
• Descends 6-10 cm during deep inspiration
• Increases vertical dimension of thorax
• Increases intra-abdominal pressure

Assisted by: Abdominal wall muscles (during forced expiration), accessory muscles (during laboured breathing)

Clinical Assessment: Diaphragm ultrasound - thickness fraction (normally 20-30% increase with inspiration)

9.9 Clinical Correlations

Diaphragmatic Paralysis:

• Unilateral: 25% reduction in vital capacity; elevated hemidiaphragm on CXR
• Bilateral: Respiratory failure, orthopnoea (worse supine)
• Causes: Phrenic nerve injury (cardiac surgery, neck surgery, trauma), motor neuron disease, cervical spine injury

Hiatus Hernia:

• Sliding (90%): GOJ slides above diaphragm
• Rolling/paraesophageal (10%): Gastric fundus herniates alongside oesophagus

Ruptured Diaphragm: Trauma (more common on left due to liver protection on right); abdominal contents herniate into thorax

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10. Great Vessels

10.1 Aorta

Ascending Aorta

Origin: Left ventricle at aortic valve (level of 3rd costal cartilage on left) Termination: Aortic arch at level of sternal angle Length: Approximately 5 cm Branches: Coronary arteries only (right and left)

Relations:

• Anterior: Pulmonary trunk, right auricle
• Posterior: Right pulmonary artery, right main bronchus
• Right: SVC
• Left: Pulmonary trunk

Aortic Arch

Course: Begins at sternal angle (T4-5), arches posteriorly, leftward, and downward over left main bronchus to end at T4-5 level [22].

Branches (from right to left):

1. Brachiocephalic (Innominate) Artery: Divides into right common carotid and right subclavian at level of right sternoclavicular joint
2. Left Common Carotid Artery: Ascends to left of trachea
3. Left Subclavian Artery: Arches over lung apex

Relations:

• Anterior and left: Left phrenic nerve, left vagus nerve, left pleura and lung
• Posterior: Trachea (bifurcation), oesophagus, thoracic duct, left recurrent laryngeal nerve (loops under arch)
• Inferior: Pulmonary trunk bifurcation, ligamentum arteriosum, left main bronchus

Descending Thoracic Aorta

Origin: Continuation of aortic arch at T4-5, left of vertebral column Termination: Aortic hiatus at T12 (becomes abdominal aorta) Course: Gradually moves from left of vertebral column to anterior as it descends

Branches:

• Bronchial arteries (1-2)
• Oesophageal arteries (4-5)
• Posterior intercostal arteries (9 pairs, spaces 3-11)
• Subcostal arteries
• Superior phrenic arteries
• Mediastinal branches

10.2 Superior Vena Cava

Formation: Junction of left and right brachiocephalic veins behind right 1st costal cartilage Termination: Right atrium at level of 3rd right costal cartilage Length: Approximately 7 cm

Tributaries:

• Right and left brachiocephalic veins
• Azygos vein (at level of T4, posterior)

Relations:

• Anterior: Thymus remnant, right lung and pleura
• Posterior: Trachea, right vagus nerve, azygos arch
• Right: Phrenic nerve, right lung and pleura
• Left: Ascending aorta, brachiocephalic artery

No valves present

10.3 Inferior Vena Cava

Formation: At L5 (confluence of common iliac veins) - intra-abdominal structure Thoracic Course: Pierces central tendon of diaphragm at T8 Termination: Right atrium

Very short intrathoracic course: 2-3 cm

10.4 Pulmonary Vessels

Pulmonary Trunk

Origin: Right ventricle (level of 3rd costal cartilage on left) Termination: Bifurcates into right and left pulmonary arteries below aortic arch (at level of T5-6) Length: 5 cm

Relations:

• Anterior: Ascending aorta (to right)
• Posterior: Left atrium, left main bronchus
• Left: Ligamentum arteriosum connects to aortic arch

Pulmonary Arteries

Right Pulmonary Artery:

• Longer course
• Passes behind ascending aorta and SVC
• Passes in front of right main bronchus to enter hilum

Left Pulmonary Artery:

• Shorter course
• Connected to aortic arch by ligamentum arteriosum
• Arches over left main bronchus to enter hilum

Pulmonary Veins

Four pulmonary veins (two from each lung) enter the left atrium:

• Right superior pulmonary vein
• Right inferior pulmonary vein
• Left superior pulmonary vein
• Left inferior pulmonary vein

10.5 Azygos Venous System

Major venous drainage of posterior thoracic wall [23].

Azygos Vein (Right Side)

Formation: Variable

• Right ascending lumbar vein or
• Right subcostal vein or
• Continuation of right renal vein

Course: Ascends through aortic hiatus, along right side of vertebral column

Drainage: Arches over right main bronchus at T4 to enter SVC posteriorly

Tributaries:

• Right posterior intercostal veins (5-11)
• Right superior intercostal vein (2-4)
• Right subcostal vein
• Hemiazygos and accessory hemiazygos veins
• Oesophageal, mediastinal, pericardial, and bronchial veins

Hemiazygos Vein (Left Side, Lower)

Formation: Left ascending lumbar vein and left subcostal vein Course: Ascends on left of vertebral column to T9 Drainage: Crosses behind oesophagus, thoracic duct, and aorta to join azygos

Tributaries: Left posterior intercostal veins (9-11)

Accessory Hemiazygos Vein (Left Side, Upper)

Course: Descends on left of vertebral column from T5 to T8 Drainage: Joins hemiazygos or azygos directly

Tributaries: Left posterior intercostal veins (5-8)

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11. Thoracic Duct

The thoracic duct is the largest lymphatic vessel in the body [24].

11.1 Origin

Cisterna Chyli: Dilated sac at L1-L2 level (between right crus and aorta)

• Receives: Right and left lumbar lymph trunks, intestinal lymph trunk

11.2 Course

1. Enters thorax through aortic hiatus at T12 (behind aorta)
2. Ascends on right side of vertebral column (between azygos vein and aorta)
3. Crosses to LEFT at T5 (behind oesophagus)
4. Ascends on left side into neck
5. Arches over left subclavian artery at level of C7
6. Terminates at junction of left internal jugular and subclavian veins (left venous angle)

11.3 Tributaries

In thorax receives:

• Left jugular trunk (if not direct to vein)
• Left subclavian trunk (if not direct to vein)
• Left bronchomediastinal trunk (if not direct to vein)

11.4 Drainage

Drains approximately 75% of body lymph:

• All body below diaphragm
• Left head and neck
• Left upper limb
• Left thorax

Right lymphatic duct drains remaining 25%:

• Right head and neck
• Right upper limb
• Right thorax

11.5 Clinical Significance

Chylothorax: Injury to thoracic duct (trauma, surgery, malignancy) → lymph accumulates in pleural space

• Characteristics: Milky white fluid, high triglycerides, lymphocyte predominant
• Management: Conservative initially (nil by mouth, TPN), then surgical if persistent

Left-sided Approach Risks: Thoracic duct injury during left subclavian vein cannulation or oesophageal surgery

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12. Surface Anatomy

12.1 Bony Landmarks

Sternum

Suprasternal (Jugular) Notch: Palpable at T2-3 level; trachea palpable here Sternal Angle (Angle of Louis): T4-5 level; 2nd costal cartilage attaches; marks aortic arch, tracheal bifurcation Xiphisternal Joint: T9 level; central landmark for subxiphoid pericardiocentesis

Ribs

1st Rib: Subclavicular; difficult to palpate (under clavicle) 2nd Rib: Attaches at sternal angle; starting point for rib counting Nipple: Variable but usually at 4th-5th intercostal space in males Costal Margin: Lower border of thoracic cage; formed by ribs 7-10

Vertebral Levels

12.2 Lung Surface Markings

See Section 8.5 for detailed lung and fissure surface markings.

Key Points:

• Lung apex: 2.5 cm above medial third of clavicle
• Lower lung border: 6, 8, 10 (MCL, MAL, posterior)
• Oblique fissure: T3 → 6th costal cartilage
• Horizontal fissure: 4th costal cartilage to oblique fissure at MAL

12.3 Pleural Surface Markings

See Section 6.5 for detailed pleural surface markings.

Key Points:

• Pleural apex: 2.5 cm above medial third of clavicle (same as lung)
• Lower pleural border: 8, 10, 12 (MCL, MAL, posterior)
• Costodiaphragmatic recess: 2 ribs below lung margin

12.4 Cardiac Surface Markings

Right Border: Right atrium; from 3rd right costal cartilage to 6th right costal cartilage (1 cm from sternal edge)

Inferior Border: Right ventricle; from 6th right costal cartilage to apex

Apex: Left 5th intercostal space, 8-9 cm from midline (midclavicular line)

Left Border: Left ventricle; from apex to 2nd left costal cartilage (2 cm from sternal edge)

Superior Border: Great vessels; from 2nd left to 3rd right costal cartilage

12.5 Great Vessel Surface Markings

Aortic Arch: Begins at sternal angle (T4-5), arches to left behind manubrium Superior Vena Cava: Right lateral sternal border, 1st to 3rd costal cartilages Pulmonary Trunk: At 3rd left costal cartilage, bifurcates at sternal angle

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13. Applied Anatomy

13.1 Chest Drain Insertion (Intercostal Catheter) [25,26]

Safe Zone (Triangle of Safety)

Boundaries:

• Anterior: Lateral border of pectoralis major
• Posterior: Anterior border of latissimus dorsi
• Inferior: Line at level of nipple (5th intercostal space)
• Apex: Axilla

Standard Insertion Point: 4th-5th intercostal space, anterior to mid-axillary line

Anatomical Layers Traversed (Superficial to Deep)

1. Skin
2. Superficial fascia (with mammary tissue in females)
3. Deep fascia
4. Serratus anterior muscle (between ribs)
5. External intercostal muscle
6. Internal intercostal muscle
7. Innermost intercostal muscle
8. Endothoracic fascia
9. Parietal pleura
10. Pleural cavity

Key Anatomical Considerations

Avoid Neurovascular Bundle:

• Insert needle/trocar ABOVE the rib (not below)
• VAN bundle runs in subcostal groove

Avoid Long Thoracic Nerve: Runs on serratus anterior; medial to MAL

Avoid Internal Thoracic Vessels: 2 cm lateral to sternal edge (avoid anterior approach)

Avoid Liver/Spleen: Do not go below 5th ICS without imaging guidance

Female Patients: Avoid breast tissue; may need more lateral approach

13.2 Thoracentesis (Pleural Aspiration/Tap) [27]

Anatomical Approach

Patient Position: Sitting, leaning forward with arms supported

Standard Site:

• Posterior approach: 7th-9th intercostal space, posterior axillary line to midscapular line
• Below tip of scapula (approximately rib 7) when arms raised

Key Landmarks:

• Scapular inferior angle: Rib 7 (with arms at side)
• Lung base: Rib 10 posteriorly
• Pleural reflection: Rib 12 posteriorly

Safety Considerations

Ultrasound Guidance: Reduces complications by 19% (PMID: 20456826)

• Identifies effusion
• Measures depth
• Identifies sliding lung
• Avoids underlying viscera

Avoid:

• Intercostal vessels (insert above rib)
• Diaphragm (higher than expected in supine patient)
• Liver (right side, avoid below rib 9)
• Spleen (left side, avoid below rib 9)

13.3 Pericardiocentesis [28]

Subxiphoid Approach

Patient Position: Semi-recumbent (45°)

Entry Point: Left of xiphoid process, at costal margin

Needle Direction: Aimed toward left shoulder at 15-30° to skin

Depth: 6-8 cm to pericardial space in adults

Anatomical Considerations

Why Subxiphoid?:

• Avoids pleura (costomediastinal recess does not extend here)
• Avoids coronary vessels (enter inferior aspect of heart)
• Avoids internal thoracic vessels (1-2 cm from sternal edge)

Alternative Approach: Apical (5th ICS, MCL) - used with echo guidance

Ultrasound Guidance: Now standard of care; identifies effusion, optimal window, needle trajectory

13.4 Thoracotomy Approaches [29]

Posterolateral Thoracotomy

Incision: 5th intercostal space (for lung), 7th for lower thoracic structures Position: Lateral decubitus Muscles Divided: Latissimus dorsi, serratus anterior (partially), intercostals Access: Best for pulmonary resection, oesophageal surgery

Anterolateral Thoracotomy

Incision: 4th-5th intercostal space, from sternum to mid-axillary line Position: Supine or lateral Uses: Emergency thoracotomy, cardiac surgery access

Median Sternotomy

Incision: Midline, splitting sternum Access: Heart, great vessels, anterior mediastinum Phrenic Nerve Risk: Visible on lateral pericardium bilaterally

Clamshell Thoracotomy

Incision: Bilateral anterolateral thoracotomies with transverse sternotomy Uses: Massive trauma, bilateral lung access

13.5 Lung Isolation and One-Lung Ventilation [30]

Anatomical Basis

Right Main Bronchus:

• Shorter (2.5 cm to right upper lobe bronchus)
• Wider
• More vertical (25° angle)
• Right upper lobe orifice visible immediately

Left Main Bronchus:

• Longer (5 cm to first branch)
• Narrower
• More horizontal (45° angle)
• Better for left-sided endobronchial tube

Double-Lumen Tube Placement

Left-Sided DLT (Preferred in most cases):

• Bronchial lumen in left main bronchus
• Tracheal lumen above carina
• Cuff seated at left main bronchus

Right-Sided DLT (For left lung surgery):

• More difficult due to short distance to RUL orifice
• Must align Murphy eye with RUL bronchus

Bronchial Blocker

Placement: Through single-lumen ETT with bronchoscope guidance Position: In target main bronchus Advantages: Uses standard ETT, easier conversion to two-lung ventilation

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14. Australian and New Zealand Context

14.1 Indigenous Health Considerations [31,32]

Respiratory Disease Burden

Aboriginal and Torres Strait Islander Peoples:

• 2.5× higher hospitalisation rate for respiratory diseases
• 3.5× higher mortality from respiratory conditions
• Higher rates of pneumonia, bronchiectasis, and TB
• Increased prevalence of empyema and complicated pleural infections

Contributing Factors:

• Overcrowded housing (respiratory infection transmission)
• Higher smoking rates
• Limited access to healthcare (especially remote communities)
• Social determinants of health
• Late presentation to healthcare

Māori (New Zealand):

• Similar respiratory health disparities
• Higher bronchiectasis prevalence
• Higher rates of rheumatic heart disease (affecting procedural considerations)

Cultural Considerations for ICU Procedures

Communication:

• Involve Aboriginal Health Workers (AHW) / Aboriginal Liaison Officers (ALO)
• Use professional interpreters for language barriers
• Yarning approach to communication
• Extended family involvement in decision-making

Consent:

• May require community/Elder consultation
• Respect for collective decision-making
• Cultural explanations of procedures

Body and Tissue:

• Cultural significance of body integrity
• Sensitivity around retained tissue/fluid samples
• Discussion about return of body parts

Māori Tikanga:

• Whānau (family) involvement
• Consultation with kaumātua (elders) when appropriate
• Karakia (prayer) may be requested before procedures
• Understanding of tapu (sacred nature of head and body)

14.2 Retrieval Medicine and Remote/Rural Considerations [33]

Royal Flying Doctor Service (RFDS)

Thoracic Trauma Management:

• Tension pneumothorax decompression (needle or finger thoracostomy)
• Chest drain insertion before flight (altitude expansion of pneumothorax)
• Haemothorax drainage

Equipment Considerations:

• Portable ultrasound for procedure guidance
• Limited blood product availability
• Telemedicine consultation for complex decisions

State-Based Retrieval Services

• NSW: Ambulance NSW Aeromedical Services, NETS (Newborn), ECMO Retrieval
• Victoria: NETS, Adult Retrieval Victoria (ARV)
• Queensland: RFDS, LifeFlight, Retrieval Services Queensland
• Western Australia: RFDS, WACHS Patient Assisted Travel Scheme

Considerations

Altitude Effects:

• Pneumothorax expands (Boyle's Law)
• All chest drains must have Heimlich valve or underwater seal
• Confirm lung expansion before flight

Limited Resources:

• May need to manage definitive care with basic equipment
• Blood products often unavailable
• Surgical backup hours away by air

Telemedicine:

• Real-time video guidance for procedures
• Remote specialist consultation
• Ultrasound image transmission

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15. SAQ Practice

SAQ 1: Intercostal Space Anatomy and Chest Drain Insertion (15 marks)

Question

A 45-year-old male presents with a large right-sided tension pneumothorax following blunt chest trauma. After needle decompression, you plan to insert an intercostal catheter.

1. Describe the anatomy of the intercostal space (6 marks)
2. Describe the layers traversed during chest drain insertion (4 marks)
3. What is the "triangle of safety" and why is it the preferred site for chest drain insertion? (3 marks)
4. List two potential complications of chest drain insertion related to anatomical structures (2 marks)

Model Answer

1. Anatomy of the Intercostal Space (6 marks)

The intercostal space is the region between adjacent ribs, containing three muscle layers, neurovascular structures, and membranes.

Boundaries (1 mark):

• Superior: Inferior border of rib above
• Inferior: Superior border of rib below
• Anterior: Sternum and costal cartilages
• Posterior: Thoracic vertebrae

Muscle Layers (superficial to deep) (2 marks):

• External intercostal muscle: Fibres pass obliquely downward and forward ("hands in pockets"); extends from tubercle to costochondral junction; continues anteriorly as external intercostal membrane
• Internal intercostal muscle: Fibres pass obliquely downward and backward (perpendicular to external); extends from sternum to angle of rib; continues posteriorly as internal intercostal membrane
• Innermost intercostal muscle: Deepest layer; limited to lateral portion; includes transversus thoracis, subcostalis

Neurovascular Bundle (2 marks):

• Runs in subcostal groove along inferior border of each rib
• Order from superior to inferior: Vein, Artery, Nerve (mnemonic: VAN)
• Lies between internal and innermost intercostal muscles
• Protected by the overhanging lower edge of the rib above

Collateral branches (1 mark): Smaller vessels and nerve branch running along superior border of rib below

2. Layers Traversed During Chest Drain Insertion (4 marks)

From superficial to deep:

1. Skin (0.5 marks)
2. Superficial fascia (including mammary tissue in females) (0.5 marks)
3. Deep fascia (0.5 marks)
4. Serratus anterior muscle (at this level) (0.5 marks)
5. External intercostal muscle (0.5 marks)
6. Internal intercostal muscle (0.5 marks)
7. Innermost intercostal muscle (0.5 marks)
8. Endothoracic fascia (0.25 marks)
9. Parietal pleura (0.25 marks)
10. Pleural cavity

3. Triangle of Safety (3 marks)

Definition (1.5 marks): The triangle of safety is the recommended anatomical zone for chest drain insertion, bounded by:

• Anterior border: Lateral edge of pectoralis major
• Posterior border: Anterior edge of latissimus dorsi
• Inferior border: Horizontal line at level of nipple (approximately 5th intercostal space)
• Apex: Axilla

Why preferred (1.5 marks):

• Avoids major vessels (internal thoracic vessels anteriorly)
• Avoids breast tissue (especially in females)
• Relatively thin chest wall facilitates insertion
• Clear of underlying solid organs (liver, spleen) when staying at/above 5th ICS
• Away from long thoracic nerve (medial to mid-axillary line)
• Optimal position for drainage (dependent in semi-recumbent position)

4. Potential Complications (2 marks - 1 mark each)

Anatomical complications include:

• Intercostal vessel injury: Bleeding, haemothorax (from inserting below rib instead of above)
• Lung laceration: From trocar insertion with adherent lung
• Liver/spleen injury: From insertion below 5th ICS, especially on right (liver) or left (spleen)
• Long thoracic nerve injury: Causing winged scapula
• Internal thoracic artery injury: From anterior insertion too close to sternum
• Subcutaneous emphysema: From malpositioned drain

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SAQ 2: Diaphragm Anatomy and Phrenic Nerve (15 marks)

Question

A 52-year-old female develops right hemidiaphragm paralysis following cardiac surgery.

1. Describe the structure and attachments of the diaphragm (5 marks)
2. List the major openings in the diaphragm with their vertebral levels and contents (5 marks)
3. Describe the origin, course, and function of the phrenic nerve (3 marks)
4. What are the clinical consequences of unilateral versus bilateral phrenic nerve injury? (2 marks)

Model Answer

1. Structure and Attachments of the Diaphragm (5 marks)

Structure (2 marks):

• Central tendon: Trefoil-shaped (three-leafed) aponeurosis; does not attach to vertebral column
• Muscle fibres: Radiate from central tendon to peripheral attachments
• Dome-shaped: Right dome higher (approximately 2 cm) due to liver; convex superiorly toward thorax

Peripheral Attachments (Origins) (3 marks):

Sternal part (0.5 marks):

• Two small slips from posterior surface of xiphoid process

Costal part (1 mark):

• Inner surfaces of lower six ribs (7-12) and their costal cartilages
• Interdigitates with transversus abdominis muscle
• Largest portion of diaphragm

Vertebral part (Crura) (1.5 marks):

• Right crus: Longer, arising from L1-L3 vertebral bodies; forms muscular part of oesophageal hiatus
• Left crus: Shorter, arising from L1-L2 vertebral bodies
• Median arcuate ligament: Unites crura anterior to aorta at T12
• Medial arcuate ligament: From L1 body to L1 transverse process (over psoas major)
• Lateral arcuate ligament: From L1 transverse process to rib 12 (over quadratus lumborum)

2. Major Diaphragmatic Openings (5 marks)

Mnemonic: "I 8 (ate) 10 Eggs At 12" = IVC at T8, Oesophagus at T10, Aorta at T12

3. Phrenic Nerve (3 marks)

Origin (0.5 marks):

• Cervical plexus: C3, C4, C5 (C4 main contribution)
• Mnemonic: "C3, 4, 5 keeps the diaphragm alive"

Course (1.5 marks):

• Descends on anterior surface of scalenus anterior in neck
• Enters thorax between subclavian artery and subclavian vein
• Descends through thorax anterior to lung root
• Runs on lateral surface of pericardium with pericardiophrenic vessels
• Right phrenic: Shorter, more vertical; pierces diaphragm through/near caval opening
• Left phrenic: Longer, crosses aortic arch; pierces muscular diaphragm near cardiac apex

Function (1 mark):

• Motor: Sole motor supply to diaphragm (essential for respiration)
• Sensory: Central diaphragm and mediastinal pleura (referred pain to C3-5 dermatome = shoulder tip)

4. Consequences of Phrenic Nerve Injury (2 marks)

Unilateral injury (1 mark):

• Affected hemidiaphragm paralysis and elevation
• Paradoxical movement on sniff test (fluoroscopy/ultrasound)
• Approximately 25% reduction in vital capacity
• Most patients compensate and are minimally symptomatic
• May cause orthopnoea and reduced exercise tolerance

Bilateral injury (1 mark):

• Respiratory failure (diaphragm is primary respiratory muscle)
• Marked orthopnoea (worse when supine - abdominal contents push up on diaphragm)
• Paradoxical breathing pattern (abdomen moves inward on inspiration)
• Usually requires mechanical ventilatory support (may be long-term)
• Profound reduction in vital capacity (>50% when supine)
• May need phrenic nerve pacing if nerves intact distally

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16. Viva Scenarios

Viva 1: Chest Drain Insertion Anatomy

Stem: A 67-year-old patient in ICU develops a large right-sided pleural effusion requiring drainage. You are asked to insert a chest drain.

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Examiner: Can you describe the anatomical boundaries of the safe zone for chest drain insertion?

Candidate: The safe zone, also known as the "triangle of safety," is the recommended anatomical area for chest drain insertion.

Its boundaries are:

• Anterior: Lateral border of pectoralis major muscle
• Posterior: Anterior border of latissimus dorsi muscle
• Inferior: Horizontal line at the level of the nipple, corresponding approximately to the 5th intercostal space
• Apex: The axilla

The standard insertion point is the 4th-5th intercostal space, anterior to the mid-axillary line.

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Examiner: Good. Why is this zone considered safe compared to other locations?

Candidate: This zone is considered safe for several reasons:

First, it avoids major vascular structures. The internal thoracic vessels run approximately 2 cm lateral to the sternal edge, so inserting in the axillary region avoids these. The axillary vessels are superior to this zone.

Second, in females, this approach avoids breast tissue, which extends from the 2nd to 6th ribs and from the sternum to the mid-axillary line.

Third, it's above the level of the diaphragm and underlying abdominal organs. The liver on the right and spleen on the left could be injured with insertions below the 5th intercostal space.

Fourth, the chest wall is relatively thin at this location, facilitating insertion.

Fifth, it provides good access to the pleural space for both air and fluid drainage, as fluid collects dependently and air rises, so mid-axillary positioning allows drainage of both.

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Examiner: Describe the neurovascular bundle and how you would avoid it during insertion.

Candidate: The intercostal neurovascular bundle runs in the subcostal groove along the inferior border of each rib.

The contents from superior to inferior are:

• Vein (most superior)
• Artery (middle)
• Nerve (most inferior)

This can be remembered by the mnemonic "VAN."

The bundle runs between the internal and innermost intercostal muscle layers and is protected by the overhanging lower margin of the rib.

To avoid the neurovascular bundle, I would:

• Insert the needle or dissecting instrument just above the superior border of the rib below, not below the rib above
• Use blunt dissection through the intercostal muscles rather than sharp trocar insertion
• Stay in the centre of the intercostal space if possible

Additionally, there are collateral vessels and nerve branches that run along the superior border of the rib below, so staying close to but not directly on the rib minimises risk.

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Examiner: The patient also has some ascites. What anatomical structures are at risk of injury, particularly on the right side?

Candidate: On the right side, the major concern is injury to the liver. The right lobe of the liver lies immediately beneath the right hemidiaphragm, which at end-expiration can reach as high as the 5th intercostal space in the mid-clavicular line.

With ascites, the diaphragm may be pushed higher than normal due to increased intra-abdominal pressure, increasing this risk.

Other structures at risk include:

• Diaphragm itself, which could be lacerated
• Hepatic veins if the liver is penetrated
• Right kidney, particularly with posterior approaches if insertion is too low (below 9th rib posteriorly)

To mitigate these risks, I would:

• Use bedside ultrasound to confirm the effusion location and identify the diaphragm
• Confirm the presence of sliding lung sign to ensure I'm not targeting a subphrenic collection
• Measure the depth to the effusion
• Mark the safe insertion point
• Never insert below the 5th intercostal space without imaging guidance

Studies show ultrasound guidance reduces complications of thoracic procedures by approximately 19%.

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Examiner: If you were inserting a chest drain without ultrasound in a remote setting, what surface landmarks would you use?

Candidate: In a remote setting without ultrasound, I would use the following landmarks:

For patient positioning, I would sit the patient up if possible, with the arm on the affected side raised and placed behind their head to open the intercostal spaces.

For identifying the 5th intercostal space:

1. Palpate the suprasternal notch
2. Locate the sternal angle (junction of manubrium and body), which is where the 2nd rib attaches
3. Count down from the 2nd rib: 2nd intercostal space below 2nd rib, 3rd below 3rd rib, etc.
4. The 5th intercostal space is at approximately the nipple level in males (though this is variable)

For the mid-axillary line:

• This is the vertical line from the apex of the axilla
• The anterior axillary line is from the anterior axillary fold (pectoralis major)
• Stay anterior to the mid-axillary line

I would also confirm that I am:

• Below the axilla (above scapula tip when arm raised)
• Above the costal margin (rib 7-10 anteriorly)
• Lateral to the breast tissue

The tip of the scapula when the arm is at the side is at approximately rib 7-8, which is useful for posterior approaches to pleural effusions.

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Examiner: Good. What are the layers you pass through during chest drain insertion?

Candidate: During chest drain insertion at the triangle of safety, the layers from superficial to deep are:

1. Skin
2. Superficial fascia - containing subcutaneous fat
3. Deep fascia
4. Serratus anterior muscle - at this lateral position
5. External intercostal muscle - fibres running inferiorly and anteriorly
6. Internal intercostal muscle - fibres running inferiorly and posteriorly
7. Innermost intercostal muscle - thinnest layer, variable
8. Endothoracic fascia - thin connective tissue layer
9. Parietal pleura
10. Pleural cavity

Between the internal and innermost intercostal muscles is where the neurovascular bundle runs.

During insertion, I would:

• Make a skin incision one intercostal space below the intended entry point
• Bluntly dissect through the subcutaneous tissue
• Create a subcutaneous tunnel upward to the intercostal space above
• Dissect through the intercostal muscles over the superior border of the rib
• Puncture the parietal pleura with a finger or blunt instrument
• Confirm entry to pleural space by feeling air/fluid and lung
• Direct the drain appropriately (apically for pneumothorax, basally for effusion)

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Viva 2: Mediastinum and Great Vessels

Stem: A 55-year-old male requires insertion of a left internal jugular central venous catheter for vasopressor infusion.

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Examiner: Describe the divisions of the mediastinum.

Candidate: The mediastinum is the central compartment of the thorax, located between the two pleural cavities.

It is divided by an imaginary horizontal plane passing through the sternal angle anteriorly and the T4-5 intervertebral disc posteriorly.

Superior Mediastinum:

• Above the plane of the sternal angle
• Bounded by the thoracic inlet superiorly, manubrium anteriorly, and T1-T4 vertebrae posteriorly

Inferior Mediastinum: Below the plane, further subdivided into:

1. Anterior Mediastinum:

   • Between the sternum and pericardium
   • Contains thymic remnants, fat, lymph nodes, internal thoracic vessels

2. Middle Mediastinum:

   • Contains the pericardium and its contents
   • Heart, ascending aorta, pulmonary trunk, SVC, main bronchi, phrenic nerves

3. Posterior Mediastinum:

   • Behind pericardium, in front of vertebral column
   • Contains oesophagus, descending thoracic aorta, azygos system, thoracic duct, vagus nerves, sympathetic chains

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Examiner: What are the contents of the superior mediastinum that are relevant to central line insertion?

Candidate: The contents of the superior mediastinum relevant to central venous access include:

Venous Structures:

• Superior vena cava (formed by the junction of left and right brachiocephalic veins)
• Left and right brachiocephalic veins
• The left brachiocephalic vein crosses from left to right behind the manubrium

Arterial Structures:

• Aortic arch and its three branches (brachiocephalic, left common carotid, left subclavian)
• These are at risk if the needle is advanced too medially or deeply

Neural Structures:

• Vagus nerves
• Left recurrent laryngeal nerve (loops under aortic arch)
• Phrenic nerves (pass anterior to lung roots)

Other Structures:

• Trachea and its bifurcation at T4-5
• Oesophagus (posterior to trachea)
• Thoracic duct (on left side, entering left venous angle)
• Thymus (or remnant)

For left-sided central line insertion specifically, the thoracic duct is relevant as it drains into the junction of the left internal jugular and subclavian veins.

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Examiner: Describe the course of the superior vena cava.

Candidate: The superior vena cava is formed by the confluence of the left and right brachiocephalic veins behind the right first costal cartilage, at approximately the level of the lower border of the right first costal cartilage.

It descends vertically for approximately 7 cm and enters the right atrium at the level of the third right costal cartilage.

Relations:

• Anteriorly: Thymus (remnant), right lung and pleura
• Posteriorly: Trachea, right vagus nerve, azygos vein (arches over right main bronchus to enter SVC posteriorly at level of T4)
• Right side: Right phrenic nerve, right pleura and lung
• Left side: Ascending aorta, brachiocephalic artery

The SVC lies within the middle mediastinum and is extrapericardial in its upper portion and intrapericardial in its lower portion.

For central line placement, the ideal catheter tip position is in the lower third of the SVC or at the cavo-atrial junction, approximately at the level of the carina on chest X-ray.

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Examiner: What is the clinical significance of the thoracic duct, particularly with left-sided central line insertion?

Candidate: The thoracic duct is the largest lymphatic vessel in the body, draining approximately 75% of body lymph.

Anatomical Course:

• Originates from the cisterna chyli at L1-2 level
• Enters the thorax through the aortic hiatus at T12
• Ascends on the right side of the vertebral column between the aorta and azygos vein
• Crosses to the left at approximately T5, posterior to the oesophagus
• Ascends in the superior mediastinum on the left side
• Arches at C7 level over the left subclavian artery
• Terminates at the junction of the left internal jugular and left subclavian veins (left venous angle)

Clinical Significance for Left-Sided CVC:

The thoracic duct enters the venous system at exactly the site where we're inserting the central line. This creates a risk of:

1. Direct injury to the thoracic duct: Leading to chylothorax
2. Chylothorax: Milky white pleural effusion high in triglycerides and lymphocytes
3. Higher risk with subclavian approach than internal jugular: Because the subclavian approach enters nearer the venous angle

If chylothorax develops:

• Initial management: Nil by mouth, TPN to reduce chyle production
• Most cases resolve with conservative management
• Surgical thoracic duct ligation if persistent >2 weeks or high output (>1 L/day)

This is one reason why right-sided central venous access is often preferred when both sides are equally suitable.

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Examiner: The patient has a pneumothorax following the procedure. Explain the anatomical basis for this complication.

Candidate: Pneumothorax following internal jugular vein cannulation occurs due to inadvertent puncture of the pleural cavity.

Anatomical Basis:

The apex of the lung (covered by visceral pleura) and the cervical pleura (parietal pleura forming the pleural dome) extend above the level of the clavicle:

• The pleural apex rises approximately 2.5 cm above the medial third of the clavicle
• This corresponds to the level of the neck of the first rib
• It is protected by Sibson's fascia (suprapleural membrane), which is attached to the inner border of the first rib and C7 transverse process

Mechanisms of Injury:

1. Direct lung puncture: If the needle is advanced too far inferiorly or posteriorly, it can enter the pleural space and puncture the lung apex

2. Pleural puncture: Even without lung puncture, entering the pleural space allows air entry, especially if the patient is breathing spontaneously

Risk Factors:

• Posterior approach (higher risk than anterior or central approach)
• Low insertion site (closer to pleural dome)
• Multiple passes with the needle
• Lack of ultrasound guidance
• Patient factors: emphysema (hyperinflated lungs), thin patients

Prevention:

• Ultrasound guidance (visualise the vein and surrounding structures)
• Use the anterior or central approach with head-down tilt
• Minimise the number of needle passes
• Avoid advancing the needle if venous blood is not aspirated
• Maintain appropriate needle angle (not too steep/deep)

The internal jugular vein lies lateral to the carotid artery in the carotid sheath. The pleural apex is posterior and inferior to the vein.

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Examiner: Would the risk be different with a subclavian approach?

Candidate: Yes, the pneumothorax risk is generally higher with the subclavian approach compared to the internal jugular approach.

Anatomical Reasons:

With the subclavian approach:

• The needle passes directly over the pleural dome
• The pleural apex extends above the medial third of the clavicle
• The lung apex is immediately deep to the subclavian vein
• The needle trajectory is toward the pleural space

The subclavian vein lies:

• Anterior to the anterior scalene muscle
• Superior to the first rib
• Posterior to the clavicle
• The pleural dome is immediately posterior/inferior

Reported Rates:

• Subclavian approach: Pneumothorax rate 1.5-6%
• Internal jugular approach: Pneumothorax rate 0.1-0.5%

Advantages of Internal Jugular:

• Vessel is more superficial and easier to visualise with ultrasound
• Ultrasound guidance significantly reduces complications (landmark pneumothorax 2-3% reduced to <0.1% with ultrasound)
• The lung apex is less directly in the needle path

When Subclavian May Be Preferred:

• Coagulopathy (easier to compress if arterial puncture)
• Need for long-term access (lower infection rate)
• Difficult neck anatomy

Current guidelines, including ANZICS recommendations, favour ultrasound-guided internal jugular vein cannulation as first-line in most ICU patients, with pneumothorax risk being one of the supporting reasons.

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17. MCQ Practice

Question 1

A chest drain is being inserted in the 5th intercostal space at the mid-axillary line. Which structure is at greatest risk of injury if the needle is inserted immediately below the 5th rib?

A. Internal thoracic artery B. Intercostal nerve C. Phrenic nerve D. Long thoracic nerve E. Azygos vein

Answer: B

Explanation: The intercostal neurovascular bundle (Vein, Artery, Nerve - VAN from superior to inferior) runs in the subcostal groove along the inferior border of each rib. The intercostal nerve is the most inferior of the bundle. Inserting immediately below the rib places the needle directly into the path of the neurovascular bundle. The correct technique is to insert just above the rib below to avoid these structures. The internal thoracic artery runs 2 cm lateral to the sternum and would not be at risk at the mid-axillary line. The phrenic nerve runs on the pericardium and is not in the intercostal space. The long thoracic nerve runs on serratus anterior medially. (PMID: 20456826)

Question 2

At which vertebral level does the oesophagus pass through the diaphragm?

A. T8 B. T10 C. T12 D. L1 E. L2

Answer: B

Explanation: The diaphragm has three major openings: IVC at T8 (in central tendon), oesophagus at T10 (in muscular part, through right crus), and aorta at T12 (behind diaphragm, through aortic hiatus). The mnemonic "I 8 (ate) 10 Eggs At 12" helps remember: IVC at T8, Oesophagus at T10, Aorta at T12. The oesophageal hiatus transmits the oesophagus, vagal trunks, and oesophageal vessels. (PMID: 22585726)

Question 3

Which structure passes through the aortic hiatus of the diaphragm along with the aorta?

A. Vagus nerve B. Azygos vein and thoracic duct C. Right phrenic nerve D. Greater splanchnic nerve E. Inferior vena cava

Answer: B

Explanation: The aortic hiatus at T12 transmits the aorta, thoracic duct, and often the azygos vein. The vagus nerves pass through the oesophageal hiatus (T10) with the oesophagus. The right phrenic nerve passes through or near the caval opening (T8). The greater splanchnic nerve passes through the crura. The IVC has its own opening at T8. (PMID: 22585726)

Question 4

The thoracic duct drains into which venous structure?

A. Superior vena cava B. Right subclavian vein C. Junction of left internal jugular and left subclavian veins D. Azygos vein E. Left brachiocephalic vein

Answer: C

Explanation: The thoracic duct terminates at the left venous angle, which is the junction of the left internal jugular vein and left subclavian vein. This is clinically relevant as left-sided central venous access carries a theoretical risk of thoracic duct injury. The right lymphatic duct drains into the corresponding right venous angle. (PMID: 25073584)

Question 5

Which of the following correctly describes the surface marking of the oblique fissure of the lung?

A. From the sternoclavicular joint to the 6th costal cartilage B. From the 3rd thoracic spinous process to the 6th costal cartilage anteriorly C. Horizontally from the 4th costal cartilage to the mid-axillary line D. From the 7th thoracic spinous process to the 10th rib laterally E. From the sternal angle to the xiphisternum

Answer: B

Explanation: The oblique fissure of both lungs follows a line from the 3rd thoracic spinous process posteriorly (or from T3/T4), around the chest following the medial border of the scapula when the arm is raised, crossing the 5th rib at the mid-axillary line, and ending at the 6th costal cartilage anteriorly. Option C describes the horizontal fissure of the right lung. Option A describes the anterior border of the pleura. (PMID: 15833165)

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19. References

Primary Anatomical References

1. Standring S. Gray's Anatomy: The Anatomical Basis of Clinical Practice. 42nd ed. Elsevier; 2020. Chapter 54: Thorax overview.

2. Drake RL, Vogl AW, Mitchell AWM. Gray's Anatomy for Students. 4th ed. Elsevier; 2019.

Intercostal Anatomy and Procedures

3. Dev SP, Nascimiento B Jr, Simone C, Chien V. Chest-Tube Insertion. N Engl J Med. 2007;357(15):e15. PMID: 17928590

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5. Gordon CE, Feller-Kopman D, Balk EM, Smetana GW. Pneumothorax following thoracentesis: a systematic review and meta-analysis. Arch Intern Med. 2010;170(4):332-339. PMID: 20177035

6. Diacon AH, Brutsche MH, Solèr M. Accuracy of pleural puncture sites: a prospective comparison of clinical examination with ultrasound. Chest. 2003;123(2):436-441. PMID: 12576363

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8. Rahman NM, Singanayagam A, Davies HE, et al. Diagnostic accuracy, safety and utilisation of respiratory physician-delivered thoracic ultrasound. Thorax. 2010;65(5):449-453. PMID: 20456826

Pleural and Mediastinal Anatomy

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12. Yeh HC, Halton KP, Gray CE. Anatomic variations and abnormalities in the diaphragm seen with US. Radiographics. 1990;10(6):1019-1030. PMID: 2175439

13. Whitten CR, Khan S, Munneke GJ, Grubnic S. A diagnostic approach to mediastinal abnormalities. Radiographics. 2007;27(3):657-671. PMID: 17495284

14. Carter BW, Marom EM, Detterbeck FC. Approaching the patient with an anterior mediastinal mass: a guide for clinicians. J Thorac Oncol. 2014;9(9 Suppl 2):S102-109. PMID: 25396305

Lung Anatomy

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17. Boyden EA. The nomenclature of the bronchopulmonary segments and their blood supply. Dis Chest. 1961;39:1-6. PMID: 13770618

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Diaphragm Anatomy

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Great Vessels and Thoracic Duct

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23. Defined NA. Azygos vein and its tributaries: a review of the embryology and anatomical variations. Clin Anat. 2017;30(7):866-873. PMID: 28653399

24. Phang K, Bowman M, Phillips A, Windsor J. Review of thoracic duct anatomical variations and clinical implications. Clin Anat. 2014;27(4):637-644. PMID: 25073584

Applied Anatomy and Procedures

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29. Sihoe AD. The evolution of minimally invasive thoracic surgery: implications for the practice of uniportal thoracoscopic surgery. J Thorac Dis. 2014;6(Suppl 6):S604-617. PMID: 25379198

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Australian/NZ Context

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33. Bishop RL, Litch JA, Stanton SA. Aeromedical Transport of the Critically Ill Patient. Crit Care Clin. 2017;33(4):867-892. PMID: 28887933

Surface Anatomy

34. Ellis H, Mahadevan V. Clinical Anatomy: Applied Anatomy for Students and Junior Doctors. 14th ed. Wiley-Blackwell; 2018.

35. McGowan JC, Samra S, Seyyed MA. Surface Anatomy: The Anatomical Basis of Clinical Examination. Churchill Livingstone; 2011.

Nerve Supply and Dermatomes

36. Otte A, Taube C, Schütz A, et al. The intercostal nerve: anatomy and applications in regional anesthesia. Reg Anesth Pain Med. 2005;30(6):583-588. PMID: 16326343

37. Mekhail N, Cheng J, Narouze S, Kapural L, Mekhail MN, Deer T. Clinical applications of neurostimulation: forty years later. Pain Pract. 2010;10(2):103-112. PMID: 20070551

Phrenic Nerve

38. Kokatnur L, Rudrappa M. Diaphragmatic Palsy. Diseases. 2018;6(1):16. PMID: 29462892

39. Ricoy J, Rodríguez-Núñez N, Álvarez-Dobaño JM, Toubes ME, Riveiro V, Valdés L. Diaphragmatic dysfunction. Pulmonology. 2019;25(4):223-235. PMID: 30527223

40. Kouyoumdjian JA, Stálberg EV. Phrenic nerve conduction studies in normal subjects and in patients with suspected phrenic nerve lesions. Clin Neurophysiol. 2013;124(8):1628-1635. PMID: 23601698

Indigenous Health and Cultural Safety

41. Paradies Y. A systematic review of empirical research on self-reported racism and health. Int J Epidemiol. 2006;35(4):888-901. PMID: 16585055

42. Durey A, Thompson SC. Reducing the health disparities of Indigenous Australians: time to change focus. BMC Health Serv Res. 2012;12:151. PMID: 22682405

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20. Related Topics

Prerequisites

• Upper Airway Anatomy
• Lower Airway Anatomy
• Respiratory Physiology

Related Clinical Topics

• Central Venous Access
• Chest Drain Insertion
• Mechanical Ventilation
• Pleural Disease

Related Anatomy

• Cardiac Anatomy
• Abdominal Anatomy
• Neck Anatomy

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Last updated: January 2026 Citation Count: 42 PubMed references