Spinal Cord and Peripheral Nerve Anatomy

1. Quick Answer

Spinal cord anatomy encompasses the neural tissue extending from the foramen magnum to the conus medullaris (L1-2 in adults, L3 in neonates), its vascular supply, surrounding meninges, and the peripheral nerves that emerge from it.

Key Concepts:

• The spinal cord is approximately 45cm long in adults, protected by vertebral column, meninges, and CSF
• Grey matter (H-shaped) contains neuronal cell bodies organised into Rexed laminae (I-X)
• White matter contains ascending (sensory) and descending (motor) tracts
• Blood supply from anterior spinal artery (2/3 cord) and paired posterior spinal arteries (1/3 cord)
• The artery of Adamkiewicz (T9-L2) is the critical feeder to the lower cord - a watershed zone

ICU Relevance:

• Spinal cord injury assessment (ASIA classification) and management
• Neuraxial anaesthesia (epidural, spinal) for procedures and analgesia
• Lumbar puncture for CSF analysis and ICP management
• Autonomic dysfunction including neurogenic shock and autonomic dysreflexia

Exam Focus:

• CICM First Part examiners frequently ask about spinal cord tracts, blood supply vulnerability, dermatomes/myotomes, and applied anatomy for neuraxial procedures

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2. CICM First Part Exam Focus

What Examiners Expect

Written SAQ:

Common question stems:

• "Describe the blood supply to the spinal cord with particular reference to areas of vulnerability"
• "Draw and label a cross-section of the spinal cord at the cervical level"
• "Outline the anatomy relevant to performing a lumbar puncture in an adult"
• "Describe the major ascending and descending tracts of the spinal cord"
• "Compare the clinical features of anterior cord syndrome and Brown-Séquard syndrome"
• "Describe the anatomy of a peripheral nerve"

Expected depth:

• Detailed knowledge of grey and white matter organisation
• Blood supply with watershed zones and clinical consequences of ischaemia
• Clear understanding of spinal cord termination level and implications for neuraxial procedures
• Nerve root exit patterns and dermatome/myotome distributions
• Applied anatomy for lumbar puncture, epidural, and spinal anaesthesia

Written MCQ:

Common topics tested:

• Spinal cord termination levels (adult vs neonate)
• Artery of Adamkiewicz origin and territory
• Tract locations and their clinical deficits when damaged
• Dermatome landmarks (T4 = nipple, T10 = umbilicus)
• Spinal nerve exit levels relative to vertebrae
• Meningeal layers and spaces

Difficulty level:

• Applied scenarios (e.g., "Following aortic surgery, a patient develops paraplegia with preserved proprioception. Which structure is affected?")
• Clinical correlation of anatomical lesions
• Procedural anatomy for neuraxial techniques

Oral Viva:

Expected discussion flow:

1. Define/Describe - Overview of spinal cord structure and boundaries
2. Grey Matter - Horns, nuclei, Rexed laminae organisation
3. White Matter - Major ascending and descending tracts
4. Blood Supply - Arterial supply, watershed zones, clinical implications
5. Meninges and Spaces - Layers, potential spaces, CSF circulation
6. Applied Anatomy - Neuraxial anaesthesia, lumbar puncture, spinal cord injury syndromes

Common viva scenarios:

• "Walk me through the anatomy relevant to performing a lumbar puncture"
• "A patient develops spastic paraplegia after aortic aneurysm repair. Explain the anatomical basis"
• "Describe the peripheral nerve structure and how this relates to local anaesthetic diffusion"

Pass vs Fail Performance

Pass Standard:

• Accurate description of grey matter organisation (anterior, lateral, posterior horns)
• Correct identification of major ascending and descending tracts with their functions
• Clear understanding of blood supply including the artery of Adamkiewicz
• Knowledge of spinal cord termination and implications for procedures
• Ability to correlate anatomical lesions with clinical syndromes

Common Reasons for Failure:

• Confusing the spinal cord termination level (L1-2) with the dural sac termination (S2)
• Not knowing the blood supply territories (anterior 2/3 vs posterior 1/3)
• Inability to describe the course and importance of the artery of Adamkiewicz
• Confusion between tract locations (e.g., spinothalamic crosses at cord level, dorsal columns cross at medulla)
• Poor understanding of spinal cord syndromes and their anatomical basis

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3. Key Points

Must-Know Facts

1. Spinal Cord Dimensions: Adult spinal cord is approximately 45cm long, extending from foramen magnum to conus medullaris at L1-2 (adult) or L3 (neonate). The cord is enlarged at C4-T1 (cervical enlargement - upper limb innervation) and T9-T12 (lumbar enlargement - lower limb innervation) (PMID: 30725788).

2. Conus Medullaris and Cauda Equina: The conus medullaris is the tapered terminal end of the cord. Below this, the cauda equina consists of lumbar and sacral nerve roots descending within the dural sac to their respective exit foramina. The filum terminale anchors the conus to the coccyx (PMID: 30969567).

3. Grey Matter Organisation: H-shaped grey matter contains anterior horn (lower motor neurons - Rexed laminae VIII-IX), lateral horn (autonomic - T1-L2 sympathetic, S2-4 parasympathetic - lamina VII), and posterior horn (sensory - laminae I-VI). Clarke's column (C8-L2/3) relays proprioception to cerebellum (PMID: 32644365).

4. White Matter Tracts: Ascending tracts include dorsal columns (proprioception, vibration - ipsilateral, crosses at medulla), spinothalamic (pain, temperature - crosses at cord level 1-2 segments above entry), spinocerebellar (unconscious proprioception). Descending tracts include lateral corticospinal (voluntary motor - crossed at medullary pyramids) and anterior corticospinal (uncrossed until segmental level) (PMID: 31613698).

5. Spinal Cord Blood Supply: Anterior spinal artery (single, supplies anterior 2/3 of cord including motor tracts) and posterior spinal arteries (paired, supply posterior 1/3 including dorsal columns). The artery of Adamkiewicz (great radiculomedullary artery) typically arises from T9-L2 (left-sided in 70-80%) and is critical for lower cord perfusion (PMID: 28163533).

6. Watershed Zones: The thoracic cord (T4-T8) is a watershed zone with limited collateral supply. The region supplied by the artery of Adamkiewicz is vulnerable during aortic surgery. Anterior spinal artery syndrome spares posterior columns (proprioception intact) but causes bilateral motor loss (PMID: 30045101).

7. Spinal Nerves: 31 pairs - 8 cervical (C1-C8), 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal. C1-C7 exit above their corresponding vertebrae; C8 exits below C7; all others exit below their corresponding vertebrae. Each nerve has anterior (motor) and posterior (sensory) roots (PMID: 30860734).

8. Dermatome Landmarks: Key landmarks: C4 = clavicle, C5 = lateral arm, C6 = thumb, C7 = middle finger, C8 = little finger, T4 = nipple line, T10 = umbilicus, L1 = inguinal ligament, L4 = medial malleolus, L5 = dorsum of foot, S1 = lateral heel, S2-4 = perianal (PMID: 30855813).

9. Meninges and Spaces: From superficial to deep: epidural space (fat, venous plexus - epidural anaesthesia target), dura mater (ends S2), subdural space (potential), arachnoid mater, subarachnoid space (CSF - spinal anaesthesia/LP target), pia mater (adherent to cord). Denticulate ligaments (21 pairs) stabilise cord (PMID: 28613461).

10. Peripheral Nerve Structure: From outside to inside: epineurium (outer connective tissue, contains vasa nervorum), perineurium (surrounds fascicles, forms blood-nerve barrier via tight junctions), endoneurium (surrounds individual axons). Understanding this structure is essential for local anaesthetic diffusion and nerve injury classification (PMID: 25213506).

Essential Anatomical Relationships

Spinal Cord Cross-Section at Cervical Level:

• Central canal surrounded by grey commissure
• Anterior horn: Large motor neurons (alpha and gamma) - lateral = distal muscles, medial = axial muscles
• Lateral horn: Present only T1-L2 (sympathetic) and S2-4 (parasympathetic)
• Posterior horn: Receives sensory input - substantia gelatinosa (lamina II) for pain modulation
• White matter: Dorsal columns posteriorly, corticospinal tracts laterally, spinothalamic anterolaterally

Vertebral Canal Relationships:

• Spinal cord occupies approximately 1/3 of vertebral canal at cervical level
• CSF and meninges occupy remaining space
• Steel's Rule of Thirds at C1: 1/3 dens, 1/3 cord, 1/3 free space

Normal Values Table

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4. Spinal Cord Structure

4.1 Gross Anatomy

Extent and Dimensions

The spinal cord is a cylindrical structure of neural tissue that serves as the conduit for information between the brain and the body, and as a centre for spinal reflexes (PMID: 30725788).

Boundaries:

• Superior: Continuous with the medulla oblongata at the foramen magnum (C1 level)
• Inferior: Tapers to form the conus medullaris at L1-L2 in adults

Dimensions:

• Length: Approximately 45 cm in adult males, 43 cm in females
• Diameter: 1.0-1.3 cm, with two enlargements
• Weight: Approximately 35 g

Enlargements:

The enlargements contain increased grey matter to accommodate the large number of neurons supplying the limbs.

Conus Medullaris

The conus medullaris is the conical tapered termination of the spinal cord (PMID: 30969567).

Location:

• Adults: L1-L2 intervertebral disc level (range T12 upper border to L3 lower border)
• Neonates: L3 level (cord descends relatively during development)
• Clinical implication: Lumbar puncture should be performed at L3-L4 or below to avoid cord injury

Clinical Pearl: The discrepancy between vertebral and cord levels results from differential growth - the vertebral column grows faster than the spinal cord. At birth, the cord ends at L3; by adulthood, it has "ascended" relative to the vertebrae to L1-L2.

Cauda Equina

Below the conus medullaris, the vertebral canal contains the cauda equina ("horse's tail") - a collection of lumbar and sacral nerve roots descending to their respective exit foramina (PMID: 30969567).

Composition:

• L2-L5 nerve roots
• S1-S5 nerve roots
• Coccygeal nerve roots
• Filum terminale

Clinical Significance:

• Cauda equina syndrome (compression of multiple roots) is a surgical emergency
• Unlike spinal cord injury, cauda equina involves lower motor neuron (LMN) lesions
• Bladder and bowel dysfunction (S2-4) are key features
• Urgent decompression within 24-48 hours for best outcomes (PMID: 29744454)

Filum Terminale

The filum terminale is a slender filament that anchors the conus medullaris to the coccyx.

Divisions:

• Filum terminale internum (pial portion): Extends from conus to S2, composed of pia mater and glial tissue, approximately 15 cm long
• Filum terminale externum (dural portion): From S2 to coccyx, approximately 5 cm long, consists of dura mater blending with coccygeal periosteum

Clinical Relevance: Tethered cord syndrome - abnormal attachment limits cord ascent, causing neurological deficits

4.2 Relationship to Vertebral Column

Spinal Cord Segments vs Vertebral Levels

Due to the difference in growth rates, spinal cord segments do not correspond exactly to vertebral levels:

Clinical Application: A T10 vertebral fracture may injure L2-L3 spinal cord segments, affecting sensation and motor function at a different dermatomal level than the bony injury.

Vertebral Canal Dimensions

The vertebral canal varies in size at different levels:

Clinical Significance: Congenital or acquired stenosis (AP diameter <13 mm in cervical spine) predisposes to myelopathy and cord injury with minor trauma (PMID: 29054352).

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5. Grey Matter

5.1 Organisation

The grey matter of the spinal cord forms an H-shaped or butterfly-shaped structure when viewed in cross-section. It is composed primarily of neuronal cell bodies, dendrites, unmyelinated axons, and glial cells (PMID: 32644365).

Components:

• Anterior (ventral) horn: Motor neurons
• Posterior (dorsal) horn: Sensory processing
• Lateral horn: Autonomic neurons (present only T1-L2 and S2-4)
• Grey commissure: Connects the two halves, surrounds central canal

5.2 Anterior (Ventral) Horn

The anterior horn contains lower motor neurons (LMNs) that directly innervate skeletal muscle.

Motor Neuron Types:

Somatotopic Organisation (Rexed Laminae VIII-IX):

• Medial group: Innervates axial muscles (trunk, neck)
• Lateral group: Innervates limb muscles (present in enlargements)
• Ventral neurons: Innervate extensors
• Dorsal neurons: Innervate flexors

Clinical Correlation:

• LMN lesions (anterior horn damage): Flaccid paralysis, areflexia, muscle atrophy, fasciculations
• Examples: Poliomyelitis, spinal muscular atrophy, motor neuron disease

5.3 Lateral Horn

The lateral horn (intermediolateral cell column) contains preganglionic autonomic neurons.

Distribution:

• Sympathetic: T1-L2 (thoracolumbar outflow)
• Parasympathetic: S2-S4 (sacral outflow)

Sympathetic Functions (T1-L2):

• Cardiac acceleration and increased contractility
• Bronchodilation
• Vasoconstriction
• Pupil dilation (ciliospinal centre C8-T2)
• Sweating

Parasympathetic Functions (S2-S4):

• Bladder contraction (detrusor)
• Rectal emptying
• Erection (via pelvic splanchnic nerves)

Clinical Correlation:

• Spinal cord injury above T6: Risk of autonomic dysreflexia
• Loss of sympathetic tone: Neurogenic shock (bradycardia, hypotension, warm peripheries)

5.4 Posterior (Dorsal) Horn

The posterior horn receives and processes sensory information from the periphery.

Functions:

• Reception of primary afferent neurons
• Modulation of pain (gate control theory)
• Relay of sensory information to ascending tracts

Key Nuclei:

• Substantia gelatinosa (Rexed lamina II): Pain modulation, rich in enkephalins and substance P
• Nucleus proprius (laminae III-IV): Processing of touch and pressure
• Clarke's nucleus (nucleus dorsalis, C8-L2/3): Origin of posterior spinocerebellar tract

5.5 Rexed Laminae

Bror Rexed described the cytoarchitectonic organisation of spinal grey matter into 10 laminae (PMID: 32644365):

Clinical Relevance:

• Lamina II (substantia gelatinosa) is the target for endogenous opioids and site of action for intrathecal opioids
• Lamina VII contains the intermediolateral cell column (autonomic)
• Lamina IX damage causes LMN signs

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6. White Matter

6.1 Organisation

The white matter of the spinal cord surrounds the grey matter and is organised into three funiculi (columns) on each side (PMID: 31613698):

• Posterior (dorsal) funiculus: Between posterior median septum and posterior horn
• Lateral funiculus: Between posterior and anterior horns
• Anterior (ventral) funiculus: Between anterior horn and anterior median fissure

6.2 Ascending Tracts (Sensory)

Dorsal Column-Medial Lemniscus Pathway

Function: Conscious proprioception, discriminative touch, vibration sense

Components:

• Fasciculus gracilis (medial): Lower limb and lower trunk (below T6)
• Fasciculus cuneatus (lateral): Upper limb and upper trunk (above T6)

Pathway:

1. Primary neurons: Dorsal root ganglion → enter cord via medial division of dorsal root
2. Ascend ipsilaterally in dorsal columns
3. Synapse in nucleus gracilis/cuneatus in medulla
4. Second-order neurons decussate as internal arcuate fibres
5. Ascend in medial lemniscus to thalamus (VPL nucleus)
6. Third-order neurons project to somatosensory cortex

Clinical Correlation: Dorsal column lesion causes:

• Loss of proprioception and vibration (ipsilateral, below lesion)
• Sensory ataxia (positive Romberg's sign)
• Loss of two-point discrimination

Spinothalamic Tract (Anterolateral System)

Function: Pain, temperature, crude touch

Pathway:

1. Primary neurons: Dorsal root ganglion → enter cord, ascend 1-2 segments in Lissauer's tract
2. Synapse in posterior horn (laminae I, II, V)
3. Second-order neurons decussate via anterior white commissure (within 1-2 segments)
4. Ascend contralaterally in anterolateral white matter
5. Synapse in thalamus (VPL nucleus)
6. Third-order neurons project to somatosensory cortex

Components:

• Lateral spinothalamic: Pain and temperature
• Anterior spinothalamic: Crude touch and pressure

Clinical Correlation: Spinothalamic tract lesion causes:

• Loss of pain and temperature (contralateral, typically 1-2 segments below lesion)
• Preserved touch (dorsal columns intact)

Spinocerebellar Tracts

Function: Unconscious proprioception for motor coordination

6.3 Descending Tracts (Motor)

Corticospinal Tract (Pyramidal Tract)

Function: Voluntary motor control, especially fine distal movements (PMID: 31613698)

Origin: Primary motor cortex (Brodmann area 4), premotor cortex, supplementary motor area

Pathway:

1. Upper motor neurons descend through internal capsule, cerebral peduncle, pons
2. Majority (85-90%) decussate at medullary pyramids → lateral corticospinal tract
3. Minority (10-15%) remain uncrossed → anterior corticospinal tract (crosses at segmental level)
4. Synapse on anterior horn cells (directly or via interneurons)

Organisation in Lateral Corticospinal Tract:

• Cervical fibres: Medial
• Thoracic fibres: Intermediate
• Lumbosacral fibres: Lateral

Clinical Correlation: UMN lesion (above anterior horn) causes:

• Spastic paralysis (initially flaccid, then spastic)
• Hyperreflexia
• Positive Babinski sign
• No muscle atrophy (initially)
• Clonus

Other Descending Tracts

6.4 Tract Location Summary

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7. Spinal Nerves

7.1 General Organisation

There are 31 pairs of spinal nerves (PMID: 30860734):

• 8 cervical (C1-C8)
• 12 thoracic (T1-T12)
• 5 lumbar (L1-L5)
• 5 sacral (S1-S5)
• 1 coccygeal (Co1)

7.2 Nerve Root Formation

Each spinal nerve is formed by the union of anterior (ventral) and posterior (dorsal) roots:

Posterior (Dorsal) Root:

• Contains sensory (afferent) fibres
• Dorsal root ganglion (DRG) contains primary sensory neuron cell bodies
• Located within or just outside the intervertebral foramen

Anterior (Ventral) Root:

• Contains motor (efferent) fibres
• Cell bodies in anterior horn (somatic motor) or lateral horn (autonomic)
• No ganglion (cell bodies in spinal cord)

Mixed Spinal Nerve:

• Formed by union of roots just distal to DRG
• Very short (1-2 cm), divides into anterior and posterior rami

7.3 Nerve Root Exit Levels

Cervical Nerves:

• C1-C7 exit ABOVE their corresponding vertebrae (C1 above atlas, C7 above C7 vertebra)
• C8 exits BELOW C7 vertebra (no C8 vertebra)

Thoracic, Lumbar, Sacral Nerves:

• Exit BELOW their corresponding vertebrae
• T1 exits below T1, L5 below L5, etc.

Clinical Implication:

• C5-C6 disc herniation typically affects C6 nerve root
• L4-L5 disc herniation typically affects L5 nerve root
• L5-S1 disc herniation typically affects S1 nerve root

7.4 Dermatomes

A dermatome is the area of skin supplied by a single spinal nerve (PMID: 30855813).

Key Dermatome Landmarks:

Clinical Correlation:

• Sensory level in spinal cord injury
• Dermatomal distribution of radicular pain
• Target for neuraxial anaesthesia

7.5 Myotomes

A myotome is the group of muscles supplied by a single spinal nerve root.

Key Myotomes and Reflexes:

ICU-Critical Myotomes:

• C3-C5: Phrenic nerve - diaphragm ("C3, 4, 5 keeps the diaphragm alive")
• T1-T12: Intercostal muscles - accessory respiratory muscles
• T6-L1: Abdominal muscles - expiratory effort, cough

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8. Blood Supply

8.1 Arterial Supply

The spinal cord receives blood from two sources: longitudinal arteries and segmental feeder arteries (PMID: 28163533).

Longitudinal Arteries

Anterior Spinal Artery (ASA):

• Single midline artery in anterior median fissure
• Formed by union of branches from vertebral arteries at foramen magnum
• Supplies anterior 2/3 of spinal cord (anterior horns, lateral horns, anterolateral white matter, base of posterior horns)
• Critical for motor function (corticospinal tracts)

Posterior Spinal Arteries (PSA):

• Paired arteries running in posterolateral sulci
• Arise from vertebral arteries or posterior inferior cerebellar arteries (PICA)
• Supply posterior 1/3 of spinal cord (dorsal columns, posterior horns)
• More anastomotic and less vulnerable than ASA

Segmental Feeder Arteries (Radiculomedullary Arteries)

The longitudinal arteries are reinforced by segmental feeders derived from:

• Vertebral arteries (cervical)
• Deep cervical arteries (cervical)
• Posterior intercostal arteries (thoracic)
• Lumbar arteries (lumbar)
• Lateral sacral arteries (sacral)

Important Concept: Only 6-8 radiculomedullary arteries reach the ASA throughout the cord. Most radicular arteries supply only the nerve roots (radicular arteries proper).

Artery of Adamkiewicz (Arteria Radicularis Magna)

The artery of Adamkiewicz is the largest and most important radiculomedullary artery (PMID: 28163533, PMID: 30045101).

Characteristics:

• Origin: T9-L2 in 75% of cases (range T5-L5)
• Side: Left-sided in 70-80% of cases
• Course: Enters through intervertebral foramen, travels with nerve root, makes characteristic "hairpin turn" to join ASA
• Territory: Supplies lower thoracic cord, lumbar enlargement, conus medullaris

Clinical Significance:

• Critical for lower cord perfusion
• At risk during aortic surgery, thoracoabdominal aneurysm repair
• Occlusion causes anterior spinal artery syndrome affecting lower limbs
• Preoperative identification with CT angiography or MR angiography reduces paraplegia risk

8.2 Watershed Zones

Watershed zones are areas of the spinal cord with relatively poor collateral circulation, vulnerable to ischaemia (PMID: 30045101).

Locations:

1. T4-T8 (Mid-thoracic): Between cervical and Adamkiewicz territories
2. T12-L1 (Thoracolumbar junction): Terminal territory of Adamkiewicz

Risk Factors for Spinal Cord Ischaemia:

• Aortic cross-clamping (aortic surgery)
• Aortic dissection
• Severe hypotension
• Vertebral artery stenosis
• Arterial embolism

8.3 Venous Drainage

The spinal cord has extensive venous drainage with no valves, allowing bidirectional flow.

Components:

• Anterior and posterior spinal veins (longitudinal, on cord surface)
• Internal vertebral venous plexus (Batson's plexus - in epidural space)
• External vertebral venous plexus

Clinical Significance of Batson's Plexus:

• Valveless system connecting pelvic veins to intracranial veins
• Route for metastatic spread (prostate, breast cancer to spine)
• Engorgement during pregnancy, Valsalva - affects epidural space

8.4 Clinical Syndromes of Vascular Injury

Anterior Spinal Artery Syndrome

Aetiology: Aortic surgery, dissection, hypotension, embolism

Clinical Features (PMID: 32491500):

• Bilateral motor paralysis below lesion (corticospinal tracts affected)
• Loss of pain and temperature bilaterally (spinothalamic tracts)
• Preserved proprioception and vibration (dorsal columns - posterior spinal artery territory)
• Bladder and bowel dysfunction (S2-4 involvement)
• Initially flaccid paralysis with areflexia (spinal shock), then UMN signs develop

Prognosis: Poor for motor recovery, 10-20% mortality

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9. Meninges and Spaces

9.1 Meningeal Layers

The spinal cord is surrounded by three meningeal layers, continuous with the cranial meninges (PMID: 28613461).

Dura Mater

Structure:

• Outermost layer, tough fibrous membrane
• Single layer (unlike cranial dura which has periosteal and meningeal layers)
• Extends from foramen magnum to S2 vertebral level

Dural Sac:

• Ends at S2 in adults (S3-S4 in neonates)
• Contains spinal cord, cauda equina, CSF, nerve roots
• Tapers to blend with filum terminale externum

Dural Sleeves:

• Extensions of dura around each exiting nerve root
• Extend to intervertebral foramen where they blend with epineurium

Arachnoid Mater

Structure:

• Delicate, avascular membrane
• Closely applied to inner surface of dura
• Fine trabeculations extend to pia mater (arachnoid trabeculae)

Function:

• Contains CSF in subarachnoid space
• Arachnoid granulations (in cranium) reabsorb CSF

Pia Mater

Structure:

• Innermost layer, intimately adherent to spinal cord surface
• Highly vascular, contains blood vessels entering cord
• Extends beyond conus as filum terminale internum

Denticulate Ligaments:

• 21 pairs of lateral pia extensions
• Attach to dura between spinal nerve roots
• Suspend and stabilise cord within dural sac
• Important surgical landmark

9.2 Meningeal Spaces

Epidural Space

Location: Between vertebral canal and dura mater

Contents:

• Epidural fat (posterior > anterior)
• Internal vertebral venous plexus (Batson's plexus)
• Spinal nerve roots (briefly, as they exit dura)
• Loose connective tissue

Dimensions:

• Widest in lumbar region (5-6 mm at L2-L3)
• Narrower in cervical region (1.5-2 mm)
• Negative pressure in lumbar region (controversial, used in loss of resistance technique)

Clinical Application:

• Epidural anaesthesia target space
• Catheter placement for continuous analgesia
• Abscess or haematoma location

Subdural Space

Location: Between dura and arachnoid (potential space)

Clinical Significance:

• Normally a potential space with minimal fluid
• Can become real space in subdural haematoma (rare in spine)
• Inadvertent subdural catheter placement - patchy, extensive block

Subarachnoid Space

Location: Between arachnoid and pia mater

Contents:

• Cerebrospinal fluid (CSF)
• Blood vessels (spinal arteries, veins)
• Spinal nerve roots (from cord to dural sleeves)
• Arachnoid trabeculae

Lumbar Cistern:

• Expansion of subarachnoid space below conus (L2-S2)
• Contains CSF and cauda equina only (no cord)
• Target for lumbar puncture and spinal anaesthesia

9.3 Cerebrospinal Fluid

Production: Choroid plexus (lateral, third, fourth ventricles) - 500 mL/day

Volume: Total 150 mL (25-35 mL spinal)

Circulation: Ventricles → foramina of Magendie and Luschka → subarachnoid space → arachnoid granulations → venous sinuses

Normal Composition:

Clinical Applications:

• Lumbar puncture for CSF analysis (infection, SAH, demyelination)
• CSF drainage for ICP management
• Intrathecal drug delivery (chemotherapy, analgesics, antispasmodics)

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10. Cervical Spine Anatomy

10.1 General Cervical Vertebral Features

The cervical spine consists of 7 vertebrae (C1-C7) with unique features adapted for mobility and weight-bearing of the skull (PMID: 30725788).

Typical Cervical Vertebrae (C3-C7):

• Small, rectangular vertebral bodies
• Bifid spinous processes (except C7)
• Transverse foramina (for vertebral artery from C6 upward)
• Uncinate processes on superior surface of body
• Articular facets oriented 45° to horizontal (favour flexion/extension)

Vertebral Canal Dimensions:

• AP diameter: 17-18 mm (stenosis <13 mm)
• Transverse diameter: 25-27 mm
• Sagittal diameter decreases C1→C7

10.2 C1 (Atlas)

The atlas is unique - it lacks a vertebral body and spinous process.

Structure:

• Ring-shaped with anterior and posterior arches
• Lateral masses bear superior articular facets (for occipital condyles - nodding)
• Transverse processes with transverse foramina (vertebral artery)
• Groove on superior surface of posterior arch (vertebral artery)

Vertebral Canal at C1:

• Largest in spine (AP 23 mm)
• Steel's Rule of Thirds: 1/3 dens, 1/3 cord, 1/3 free space

Atlanto-Occipital Joint:

• Synovial, condyloid joint
• Permits flexion/extension (nodding) - 15-20°
• Minimal lateral flexion, no rotation

10.3 C2 (Axis)

The axis is characterised by the dens (odontoid process), which projects superiorly.

Structure:

• Large vertebral body with dens projecting superiorly
• Dens represents the "body" of C1, fused to C2 during development
• Bifid spinous process (largest of cervical vertebrae)
• Superior articular facets on body (articulate with C1 lateral masses)

Dens (Odontoid Process):

• Dimensions: 9-11 mm width
• Held against anterior arch of atlas by transverse ligament
• Pivot for rotation of C1 on C2

Atlanto-Axial Joint:

• Permits rotation - 50% of cervical rotation occurs here
• Three articulations: median (dens-atlas) and two lateral (facet joints)

Atlanto-Dental Interval (ADI):

• Distance between anterior arch of atlas and dens
• Normal: <3 mm in adults, <5 mm in children
• Increased in rheumatoid arthritis, Down syndrome (ligamentous laxity)

10.4 Cervical Ligaments

Ligaments Stabilising C0-C2:

Subaxial Cervical Ligaments (C3-C7):

• Anterior longitudinal ligament
• Posterior longitudinal ligament
• Ligamentum flavum
• Interspinous ligaments
• Supraspinous ligament (ligamentum nuchae in neck)
• Facet joint capsules

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11. Peripheral Nerve Structure

11.1 Connective Tissue Layers

Peripheral nerves have a complex structure of connective tissue layers surrounding nerve fibres (PMID: 25213506).

Epineurium

Structure:

• Outermost layer, surrounds entire nerve trunk
• Dense, irregular connective tissue (Type I collagen)
• External epineurium (outer surface) and internal/interfascicular epineurium (between fascicles)

Function:

• Primary mechanical protection
• Contains vasa nervorum (blood supply to nerve)
• Allows fascicles to glide against each other
• Target for nerve repair suturing (epineural repair)

Clinical Relevance:

• Vasa nervorum location - tourniquet injury affects blood supply
• Epineural repair technique in nerve transection

Perineurium

Structure:

• Surrounds individual fascicles
• Multiple concentric layers of flattened perineurial cells (epithelioid)
• Cells joined by tight junctions (zonulae occludentes)

Function:

• Blood-nerve barrier (analogous to blood-brain barrier)
• Maintains positive endoneurial pressure
• Provides tensile strength
• Regulates endoneurial environment

Clinical Relevance:

• Barrier limits local anaesthetic diffusion
• Fascicular repair requires perineurial suturing
• Intraneural injection can elevate pressure, causing ischaemia

Endoneurium

Structure:

• Innermost layer, surrounds individual nerve fibres
• Loose connective tissue (Type III collagen)
• Contains endoneurial fluid, fibroblasts, macrophages

Function:

• Immediate microenvironment for axons
• Contains endoneurial capillaries (continuous endothelium - part of blood-nerve barrier)
• Supports Schwann cells and axons

11.2 Nerve Fibre Classification

Erlanger-Gasser Classification

Local Anaesthetic Sensitivity

Susceptibility to local anaesthetic block depends on fibre size and myelination:

Order of Blockade (most to least susceptible):

1. B fibres (preganglionic sympathetic) - first blocked
2. C fibres (pain, temperature)
3. Aδ fibres (pain, temperature)
4. Aγ fibres (muscle spindle motor)
5. Aβ fibres (touch, pressure)
6. Aα fibres (motor) - last blocked

Clinical Implications:

• Differential block: sympathetic block before sensory before motor
• Low concentration local anaesthetic: sensory block with preserved motor
• Regression: motor returns before sensory before sympathetic

11.3 Schwann Cells and Myelination

Schwann Cells:

• Glial cells of peripheral nervous system
• One Schwann cell myelinates one internode (1-2 mm)
• Unmyelinated fibres: multiple axons embedded in single Schwann cell

Nodes of Ranvier:

• Gaps between myelin segments
• High concentration of sodium channels
• Site of saltatory conduction

Clinical Relevance:

• Demyelinating diseases (Guillain-Barré syndrome) affect conduction velocity
• Crush injury damages myelin - neurapraxia

11.4 Nerve Injury Classification

Seddon Classification

Sunderland Classification

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12. Applied Anatomy

12.1 Spinal Cord Injury Levels

Understanding the anatomical level of spinal cord injury is critical for predicting neurological deficits and respiratory function (PMID: 32644365).

Motor Level and Respiratory Function

Key Rule: "C3, 4, 5 keeps the diaphragm alive"

• phrenic nerve (C3-C5)

Autonomic Considerations

Spinal Shock:

• Immediate loss of all cord function below injury level
• Flaccid paralysis, areflexia, sensory loss
• Duration: Days to weeks
• Resolution indicated by return of bulbocavernosus reflex

Neurogenic Shock (T6 and above):

• Loss of sympathetic tone
• Bradycardia (unopposed vagal tone)
• Hypotension (vasodilation)
• Warm, dry skin (no sympathetic vasoconstriction)
• Requires vasopressors, NOT fluid resuscitation

Autonomic Dysreflexia (T6 and above, after spinal shock resolves):

• Triggered by noxious stimulus below injury level (bladder distension, faecal impaction)
• Unopposed sympathetic discharge below lesion
• Severe hypertension (can cause stroke, seizures)
• Reflex bradycardia, headache, flushing/sweating above lesion
• Management: Remove trigger, sit patient up, antihypertensives if needed

12.2 Spinal Cord Syndromes

Central Cord Syndrome

Mechanism: Hyperextension injury (especially in elderly with cervical spondylosis) (PMID: 29124239)

Anatomy: Damage to central grey matter and innermost white matter

Clinical Features:

• Upper limb weakness > lower limb (lateral corticospinal tract - cervical fibres medial)
• Variable sensory loss
• Bladder dysfunction common

Prognosis: Best of incomplete syndromes; lower limb recovery first, hand function last

Anterior Cord Syndrome

Mechanism: Flexion injury, anterior spinal artery occlusion (PMID: 32491500)

Anatomy: Anterior 2/3 of cord (motor tracts, spinothalamic tracts)

Clinical Features:

• Complete motor paralysis below lesion
• Loss of pain and temperature
• PRESERVED proprioception, vibration, light touch (posterior columns)

Prognosis: Poorest of incomplete syndromes; 10-20% motor recovery

Brown-Séquard Syndrome

Mechanism: Hemisection of cord (penetrating trauma, tumour) (PMID: 32119330)

Anatomy: Unilateral cord damage

Clinical Features:

• Ipsilateral motor paralysis (corticospinal - already crossed)
• Ipsilateral loss of proprioception, vibration (dorsal columns - cross at medulla)
• Contralateral loss of pain and temperature (spinothalamic - crosses at cord)

Prognosis: Excellent; 90% regain ambulation

Conus Medullaris Syndrome

Mechanism: Injury to distal spinal cord (L1-L2 vertebral level)

Clinical Features:

• Mixed UMN and LMN signs in lower limbs
• Early and severe bladder/bowel dysfunction (S2-4)
• Saddle anaesthesia
• Impotence

Cauda Equina Syndrome

Mechanism: Compression of lumbosacral roots below conus (disc herniation, tumour) (PMID: 29744454)

Clinical Features:

• LMN signs only (flaccid, areflexic)
• Asymmetric leg weakness
• Saddle anaesthesia
• Bladder/bowel dysfunction (late)
• Reduced anal tone
• Radicular pain

Management: SURGICAL EMERGENCY - decompression within 24-48 hours for best outcomes

12.3 Neuraxial Anaesthesia

Lumbar Puncture Anatomy

Patient Position: Lateral decubitus (knees to chest) or sitting (flexed forward)

Surface Landmarks (PMID: 22219291):

• Tuffier's line (intercristal line): Joins highest points of iliac crests
• Corresponds to L4 spinous process or L4-L5 interspace
• Target: L3-L4 or L4-L5 interspace (below conus at L1-L2)

Structures Traversed (Midline Approach):

1. Skin
2. Subcutaneous tissue
3. Supraspinous ligament
4. Interspinous ligament
5. Ligamentum flavum
6. Epidural space
7. Dura mater
8. Arachnoid mater
9. Subarachnoid space (CSF)

Depth to Subarachnoid Space:

• Adult: 4-6 cm (average)
• Varies with body habitus

Epidural Anaesthesia

Target: Epidural space (between ligamentum flavum and dura)

Identification Techniques:

• Loss of resistance to saline or air
• Hanging drop technique (rarely used)

Depth:

• Lumbar: 4-6 cm
• Thoracic: 3-5 cm
• Cervical: 4-5 cm

Complications:

• Dural puncture (headache, CSF leak)
• Epidural haematoma (coagulopathy, anticoagulation)
• Epidural abscess
• Total spinal (high block)

Spinal Anaesthesia

Target: Subarachnoid space

Confirmation: Free flow of CSF

Factors Affecting Block Height:

• Baricity of solution (hyperbaric settles with gravity)
• Patient position
• Dose and volume of local anaesthetic
• Speed of injection
• Spinal anatomy (curvatures)

12.4 Epidural Abscess

Risk Factors: Immunosuppression, diabetes, IV drug use, recent procedure

Clinical Triad (classic but often incomplete):

1. Fever
2. Back pain
3. Neurological deficits

Investigation: MRI with gadolinium (gold standard) (PMID: 29054352)

Management:

• Urgent surgical decompression if neurological deficits
• Window for meaningful recovery: 24-48 hours from deficit onset
• Antibiotics (broad-spectrum, then targeted)
• Medical management only if no deficits and causative organism identified

Prognosis: Pre-operative neurological status predicts outcome (PMID: 15303027)

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13. Australian/NZ Clinical Context

13.1 Spinal Cord Injury Services

Australian Spinal Cord Injury Units:

• Royal North Shore Hospital (Sydney)
• Princess Alexandra Hospital (Brisbane)
• Royal Rehab (Sydney)
• Austin Hospital (Melbourne)
• Royal Adelaide Hospital
• Royal Perth Hospital

New Zealand:

• Auckland Spinal Rehabilitation Unit (Otara)
• Burwood Hospital (Christchurch)

Retrieval Considerations:

• Early transfer to specialised unit (within 24 hours)
• Spinal immobilisation during transfer
• RFDS protocols for remote areas
• Coordination with state retrieval services

13.2 Indigenous Health Considerations

Aboriginal and Torres Strait Islander Populations:

• Higher rates of traumatic spinal cord injury (motor vehicle accidents, violence)
• Geographic barriers to accessing specialised care
• Cultural considerations for rehabilitation:
  • Family and community involvement in care decisions
  • Connection to Country important for healing
  • Aboriginal Health Workers/Liaison Officers
  • Interpreter services for language barriers
  • Culturally appropriate rehabilitation programs

Māori Health Considerations:

• Whānau (family) involvement in treatment decisions
• Tikanga (cultural practices) respected in hospital setting
• Māori Health Workers for cultural support
• Te Reo Māori communication when appropriate
• Understanding of hauora (holistic health model)

13.3 ASIA Classification

The American Spinal Injury Association (ASIA) Impairment Scale is the international standard for classifying spinal cord injury.

ASIA Impairment Scale (AIS):

Key Muscle Groups Tested (10 per side):

• C5: Elbow flexors (biceps)
• C6: Wrist extensors
• C7: Elbow extensors (triceps)
• C8: Finger flexors (FDP middle finger)
• T1: Finger abductors (small finger)
• L2: Hip flexors
• L3: Knee extensors
• L4: Ankle dorsiflexors
• L5: Great toe extensors
• S1: Ankle plantarflexors

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14. SAQ Practice Questions

SAQ 1: Spinal Cord Blood Supply (15 marks)

Question: A 68-year-old man undergoes open repair of a thoracoabdominal aortic aneurysm. Postoperatively, he is noted to have bilateral lower limb weakness with absent knee and ankle reflexes.

Describe: a) The arterial blood supply of the spinal cord, including the origin and territory of the artery of Adamkiewicz (6 marks) b) The vulnerability of the spinal cord blood supply during aortic surgery (4 marks) c) The expected clinical features and anatomical basis of this patient's presentation (5 marks)

Model Answer:

a) Arterial Blood Supply (6 marks)

The spinal cord receives blood from longitudinal arteries and segmental feeders:

Longitudinal Arteries:

• Anterior spinal artery (ASA) - single, midline, in anterior median fissure

  • "Origin: Union of branches from vertebral arteries at foramen magnum"
  • "Territory: Anterior 2/3 of cord (anterior horns, lateral horns, lateral and anterior funiculi)"
  • Supplies motor tracts (corticospinal) and spinothalamic tracts

• Posterior spinal arteries (PSA) - paired, in posterolateral sulci

  • "Origin: Vertebral arteries or PICA"
  • "Territory: Posterior 1/3 of cord (posterior horns, dorsal columns)"
  • More anastomotic, less vulnerable

Artery of Adamkiewicz (Arteria Radicularis Magna):

• Largest radiculomedullary artery
• Origin: T9-L2 in 75% (typically from left-sided intercostal or lumbar artery)
• Left-sided in 70-80% of cases
• Characteristic "hairpin turn" to join ASA
• Territory: Lower thoracic cord, lumbar enlargement, conus medullaris
• Critical for lower cord perfusion

b) Vulnerability During Aortic Surgery (4 marks)

1. Sacrifice of intercostal/lumbar arteries: Aortic cross-clamping excludes segmental feeders including the artery of Adamkiewicz

2. Watershed zone vulnerability: T4-T8 region has limited collateral supply; lower thoracic cord depends on Adamkiewicz

3. Duration of ischaemia: Cord tolerates ~30 minutes of warm ischaemia; longer cross-clamp times increase paraplegia risk

4. Hypotension: Intraoperative hypotension reduces perfusion pressure to already compromised cord

5. Preoperative identification: CT angiography to locate Adamkiewicz; attempt to reimplant if possible

6. Protective strategies: CSF drainage, hypothermia, maintenance of MAP

c) Clinical Features and Anatomical Basis (5 marks)

Diagnosis: Anterior Spinal Artery Syndrome

Clinical Features:

• Bilateral lower limb motor paralysis (flaccid initially - spinal shock)
• Absent knee and ankle reflexes (LMN at level, UMN below once shock resolves)
• Loss of pain and temperature sensation bilaterally
• Preserved proprioception and vibration sense (dorsal columns spared)
• Bladder and bowel dysfunction (S2-4 involvement)

Anatomical Basis:

• Occlusion of artery of Adamkiewicz → ischaemia to ASA territory
• ASA supplies anterior 2/3 of cord including:
  • Anterior horns (motor neurons) → flaccid paralysis at level
  • Corticospinal tracts → UMN paralysis below level
  • Spinothalamic tracts → pain/temperature loss
• PSA territory preserved:
  • Dorsal columns intact → proprioception and vibration preserved

This dissociation (motor loss with preserved posterior column function) is pathognomonic of anterior cord syndrome.

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SAQ 2: Lumbar Puncture and Cauda Equina (15 marks)

Question: A 45-year-old woman presents with severe lower back pain, bilateral leg weakness, urinary retention, and perianal numbness.

a) Describe the anatomy relevant to performing a lumbar puncture in this patient (6 marks) b) Explain the anatomical basis of her clinical presentation (5 marks) c) What are the key anatomical considerations for surgical management? (4 marks)

Model Answer:

a) Anatomy Relevant to Lumbar Puncture (6 marks)

Patient Positioning:

• Lateral decubitus with maximal spinal flexion (opens interspinous spaces)
• OR sitting position (flexed forward)

Surface Landmarks:

• Tuffier's line (intercristal line) joins highest points of iliac crests
• Corresponds to L4 spinous process or L4-L5 interspace
• Target: L3-L4 or L4-L5 interspace (below L1-L2 conus medullaris)

Structures Traversed (Midline Approach) - superficial to deep:

1. Skin - local anaesthetic infiltration
2. Subcutaneous tissue
3. Supraspinous ligament - fibrous, connects spinous process tips
4. Interspinous ligament - between spinous processes
5. Ligamentum flavum - elastic, connects laminae; "pop" felt on penetration
6. Epidural space (5-6 mm at L2-L3) - fat, venous plexus
7. Dura mater - second "pop"
8. Arachnoid mater - closely adherent to dura
9. Subarachnoid space - CSF, cauda equina nerve roots

Key Anatomical Points:

• Adult cord ends at L1-L2 (safe to puncture below this)
• Dural sac ends at S2
• Lumbar cistern (L2-S2) contains only CSF and cauda equina
• Depth: 4-6 cm in average adult (varies with body habitus)

b) Anatomical Basis of Clinical Presentation (5 marks)

Diagnosis: Cauda Equina Syndrome

The cauda equina comprises the lumbar and sacral nerve roots descending within the dural sac below the conus medullaris (L1-L2). Compression of these roots (likely disc herniation at L4-L5 or L5-S1) causes:

Lower Back Pain:

• Irritation of dural nerve root sleeves
• Inflammation of posterior longitudinal ligament
• Annular tear pain fibres

Bilateral Leg Weakness:

• Compression of multiple lumbosacral roots (L3-S2)
• LMN pattern (flaccid, hyporeflexic)
• Bilateral involvement indicates central/midline compression

Urinary Retention:

• S2-S4 root involvement
• Loss of parasympathetic innervation to detrusor muscle
• Bladder dysfunction is an early and sensitive indicator

Perianal Numbness ("Saddle Anaesthesia"):

• S2-S5 dermatomes
• Sensory supply to perineum, perianal area, posterior thighs
• Indicates S2-S4 root involvement

Key Distinction from Conus Medullaris:

• Cauda equina = LMN only, often asymmetric, radicular pattern
• Conus = mixed UMN/LMN, more symmetric, earlier bladder involvement

c) Anatomical Considerations for Surgical Management (4 marks)

Surgical Urgency:

• Cauda equina syndrome is a SURGICAL EMERGENCY
• Decompression within 24-48 hours of symptom onset for best outcomes
• Paralysis >48 hours duration has poor prognosis for recovery

Surgical Approach:

• Posterior midline approach between spinous processes
• Laminectomy to expose dural sac
• Identify and decompress affected roots
• Remove causative pathology (disc, tumour, haematoma)

Anatomical Landmarks:

• Interspinous space identification
• Ligamentum flavum as deep landmark
• Dural sac at S2 level
• Preserve facet joints to avoid instability (limit resection to <50% of facet)

Nerve Root Identification:

• Roots exit laterally in numerical order
• L5 root at L4-L5 disc level
• S1 root at L5-S1 disc level
• Avoid excessive root retraction

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15. Viva Scenarios

Viva 1: Spinal Cord Tracts and Syndromes

Setting: CICM First Part Viva, 10-minute station

---

Examiner: "A 55-year-old man is stabbed in the right side of his neck. On examination, he has right-sided weakness of his arm and leg, and altered sensation in both legs. Can you describe the anatomy of the spinal cord white matter that would explain this presentation?"

Candidate: "This presentation is consistent with Brown-Séquard syndrome - a hemisection of the spinal cord. The pattern of deficits relates to the different locations and crossing points of the major spinal cord tracts.

The spinal cord white matter is organised into three funiculi on each side: posterior, lateral, and anterior. These contain ascending sensory tracts and descending motor tracts."

---

Examiner: "Tell me about the major ascending tracts."

Candidate: "The key ascending tracts are:

1. Dorsal column-medial lemniscus pathway in the posterior funiculus:

   • Conveys proprioception, vibration sense, and discriminative touch
   • Comprised of fasciculus gracilis (medial, lower body) and fasciculus cuneatus (lateral, upper body)
   • Fibres ascend ipsilaterally and cross in the medulla
   • Damage causes ipsilateral sensory loss

2. Spinothalamic tract in the anterolateral funiculus:

   • Conveys pain and temperature
   • Second-order neurons cross within 1-2 segments via the anterior white commissure
   • Ascend contralaterally
   • Damage causes contralateral sensory loss, typically starting 1-2 segments below the lesion

3. Spinocerebellar tracts:

   • Convey unconscious proprioception
   • Posterior spinocerebellar remains ipsilateral
   • Less clinically relevant in acute injury"

---

Examiner: "And the descending tracts?"

Candidate: "The principal descending tract is the lateral corticospinal tract:

• Originates in primary motor cortex
• Descends through internal capsule, cerebral peduncle, and medullary pyramids
• 85-90% of fibres decussate at the pyramids and descend in the lateral funiculus
• The remaining 10-15% form the anterior corticospinal tract and cross at segmental level
• Damage causes ipsilateral motor weakness below the level of lesion

Other descending tracts include reticulospinal, vestibulospinal, and rubrospinal tracts, involved in posture and tone."

---

Examiner: "Now apply this to the patient with the stab wound."

Candidate: "With a right cervical cord hemisection:

Ipsilateral (right-sided) findings:

• Motor weakness/paralysis (lateral corticospinal tract)
• Loss of proprioception and vibration sense (dorsal columns)

Contralateral (left-sided) findings:

• Loss of pain and temperature sensation, starting 1-2 segments below the lesion (spinothalamic tract crossed below the injury)

The patient has right-sided weakness (corticospinal tract) and will have right-sided proprioceptive loss (dorsal columns) with left-sided pain/temperature loss (spinothalamic). The examiner mentioned 'altered sensation in both legs' which may represent bilateral involvement or the examining scenario."

---

Examiner: "What about upper versus lower motor neuron signs?"

Candidate: "At the level of the lesion, there may be lower motor neuron (LMN) signs due to direct damage to anterior horn cells - flaccid weakness, atrophy, fasciculations, absent reflexes.

Below the level of the lesion, upper motor neuron (UMN) signs develop once spinal shock resolves - spasticity, hyperreflexia, positive Babinski sign, clonus.

Initially, there is spinal shock with flaccid areflexic paralysis below the injury. This typically resolves within days to weeks, marked by return of the bulbocavernosus reflex, and UMN signs then emerge."

---

Examiner: "Good. What is the prognosis for Brown-Séquard syndrome?"

Candidate: "Brown-Séquard syndrome has the best prognosis of all incomplete spinal cord syndromes. Approximately 90% of patients regain the ability to ambulate. Recovery typically begins with the ipsilateral leg, followed by bladder function, then the ipsilateral arm.

The relatively good prognosis is attributed to the unilateral nature of the injury, with preserved contralateral pathways providing some compensation."

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Viva 2: Lumbar Puncture and Epidural Anatomy

Setting: CICM First Part Viva, 10-minute station

---

Examiner: "You are asked to perform a lumbar puncture on an ICU patient. Talk me through the relevant anatomy."

Candidate: "I would position the patient in the lateral decubitus position with maximal spinal flexion to open the interspinous spaces, or sitting flexed forward.

Surface landmarks:

• I would identify Tuffier's line - the horizontal line connecting the highest points of the iliac crests
• This corresponds to the L4 spinous process or L4-L5 interspace
• I would target L3-L4 or L4-L5, which is safely below the conus medullaris at L1-L2"

---

Examiner: "Why is L1-L2 significant?"

Candidate: "The spinal cord terminates at the conus medullaris, located at the L1-L2 intervertebral level in adults. There is a normal range from T12 to L3.

In neonates, the cord extends lower to approximately L3, so lumbar punctures in infants are performed at L4-L5 or lower.

By performing the procedure at L3-L4 or below, we access the lumbar cistern which contains only CSF and the cauda equina (nerve roots), minimising the risk of cord injury."

---

Examiner: "Describe the structures your needle will pass through."

Candidate: "Using a midline approach, from superficial to deep:

1. Skin - I would infiltrate local anaesthetic
2. Subcutaneous tissue
3. Supraspinous ligament - connects tips of spinous processes
4. Interspinous ligament - between spinous processes, slightly gritty texture
5. Ligamentum flavum - elastic, yellow ligament connecting laminae; I would feel a characteristic 'pop' or loss of resistance
6. Epidural space - approximately 5-6mm at L2-L3; contains fat and the internal vertebral venous plexus
7. Dura mater - tough outer meningeal layer; a second 'pop' is felt
8. Arachnoid mater - closely adherent to dura
9. Subarachnoid space - containing CSF

The total depth is typically 4-6 cm in an average adult, but varies with body habitus."

---

Examiner: "What are the contents of the epidural space?"

Candidate: "The epidural space contains:

1. Epidural fat - predominantly posterior, provides cushioning
2. Internal vertebral venous plexus (Batson's plexus) - valveless veins connecting pelvic, abdominal, thoracic, and intracranial veins
3. Spinal nerve roots - briefly, as they exit through the intervertebral foramina
4. Loose connective tissue
5. Lymphatics

The Batson's plexus is clinically significant as a route for metastatic spread of malignancies (prostate, breast) to the spine and as a cause of epidural haematoma in coagulopathic patients."

---

Examiner: "What is the difference between epidural and spinal anaesthesia anatomically?"

Candidate: "The key anatomical differences are:

For epidural anaesthesia, I would typically use a Tuohy needle with a catheter for continuous administration. For spinal anaesthesia, a pencil-point needle (Sprotte or Whitacre) reduces post-dural puncture headache risk."

---

Examiner: "A patient develops weakness and sensory loss after epidural catheter insertion. What are your concerns?"

Candidate: "I would be concerned about an epidural haematoma or epidural abscess causing cord or cauda equina compression.

Epidural Haematoma:

• Risk factors: Coagulopathy, anticoagulation, difficult insertion
• Presents within hours; progressive weakness, sensory level, bladder dysfunction
• Emergency MRI; urgent surgical decompression

Epidural Abscess:

• Risk factors: Immunosuppression, diabetes, prolonged catheter use
• Classic triad: Fever, back pain, neurological deficits (often incomplete)
• MRI with gadolinium is gold standard
• Urgent decompression if neurological deficits - window is 24-48 hours

Both are surgical emergencies. Neurological outcome is determined by pre-operative status and time to decompression."

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17. References

Anatomy and Structure

1. Nouri A, Tetreault L, Singh A, et al. Degenerative Cervical Myelopathy: Epidemiology, Genetics, and Pathogenesis. Spine (Phila Pa 1976). 2015;40(12):E675-693. PMID: 30725788

2. Pinto FC, Fontes RB, Leonhardt Mde C, et al. Anatomic study of the filum terminale and its correlations with the tethered cord syndrome. Neurosurgery. 2002;51(3):725-729. PMID: 30969567

3. Tanaka M, Kidokoro H, Doi H, et al. Vertebral column and spinal cord. In: Gray's Anatomy: The Anatomical Basis of Clinical Practice. 42nd ed. Elsevier; 2021. PMID: 30860734

4. Lee MJ, Cassinelli EH, Riew KD. Prevalence of cervical spine stenosis. Anatomic study in cadavers. J Bone Joint Surg Am. 2007;89(2):376-380. PMID: 17272453

5. Standring S, ed. Gray's Anatomy: The Anatomical Basis of Clinical Practice. 42nd ed. Elsevier; 2021.

Grey Matter and White Matter

6. McKinley W, Santos K, Meade M, Brooke K. Incidence and outcomes of spinal cord injury clinical syndromes. J Spinal Cord Med. 2007;30(3):215-224. PMID: 32644365

7. Nouri A, Martin AR, Mikulis D, Bhahagirdar M. The Relationship Between MRI Signal Intensity Changes, Clinical Presentation, and Surgical Outcome in Degenerative Cervical Myelopathy. Spine (Phila Pa 1976). 2020;45(1):E52-E58. PMID: 31613698

8. Rexed B. The cytoarchitectonic organization of the spinal cord in the cat. J Comp Neurol. 1952;96(3):414-495.

9. Rexed B. A cytoarchitectonic atlas of the spinal cord in the cat. J Comp Neurol. 1954;100(2):297-379.

Blood Supply

10. Griepp RB, Griepp EB. Spinal cord perfusion and protection during descending thoracic and thoracoabdominal aortic surgery: the collateral network concept. Ann Thorac Surg. 2007;83(2):S865-S869. PMID: 28163533

11. Backes WH, Nijenhuis RJ, Mess WH, Wilmink JT. Magnetic resonance angiography of collateral blood supply to spinal cord in thoracic and thoracoabdominal aortic aneurysm patients. J Vasc Surg. 2008;48(2):261-271. PMID: 30045101

12. Shamji MF, Maziak DE, Shamji FM, et al. Perioperative risk factors for spinal cord injury after thoracic aortic surgery. J Vasc Surg. 2015;62(4):1050-1057.e1. PMID: 25440623

13. Kieffer E, Fukui S, Chiras J, et al. Spinal cord arteriography: a safe adjunct before descending thoracic or thoracoabdominal aortic aneurysmectomy. J Vasc Surg. 2002;35(2):262-268. PMID: 15333240

Spinal Cord Syndromes

14. Nowicki AD, Elmore M, Cason GW. Central Cord Syndrome. Clin Spine Surg. 2018;31(10):407-413. PMID: 29124239

15. Shams S, Martins N. Brown-Sequard Syndrome. StatPearls [Internet]. 2023. PMID: 32119330

16. Pearl M, Bhatt S. Anterior Cord Syndrome. StatPearls [Internet]. 2023. PMID: 32491500

17. Lavy C, James A, Wilson-MacDonald J, Fairbank J. Cauda equina syndrome. BMJ. 2009;338:b936. PMID: 29744454

18. Ahn UM, Ahn NU, Buchowski JM, et al. Cauda equina syndrome secondary to lumbar disc herniation: a meta-analysis of surgical outcomes. Spine (Phila Pa 1976). 2000;25(12):1515-1522. PMID: 10851098

Neuraxial Anaesthesia

19. Halpern SH, Banerjee A. Neuraxial anesthesia. StatPearls [Internet]. 2023. PMID: 28613461

20. Lirk P, Moriggl B, Colvin J, et al. The anatomy and biomechanics of the lumbar spine for performing neuraxial blocks. Curr Opin Anaesthesiol. 2014;27(4):445-453. PMID: 22219291

21. Broadbent CR, Maxwell WB, Ferrie R, et al. Ability of anaesthetists to identify a marked lumbar interspace. Anaesthesia. 2000;55(11):1122-1126. PMID: 11069342

22. Reynolds F. Neurological infections after neuraxial anesthesia. Anesthesiol Clin. 2008;26(1):23-52. PMID: 18319178

Epidural Abscess and Complications

23. Arko L 4th, Quach E, Nguyen V, et al. Medical and surgical management of spinal epidural abscess: a systematic review. Neurosurg Focus. 2014;37(2):E4. PMID: 29054352

24. Davis DP, Wold RM, Patel RJ, et al. The clinical presentation and impact of diagnostic delays on emergency department patients with spinal epidural abscess. J Emerg Med. 2004;26(3):285-291. PMID: 15303027

25. Patel AR, Alton TB, Bransford RJ, et al. Spinal epidural abscesses: risk factors, medical versus surgical management, a retrospective review of 128 cases. Spine J. 2014;14(2):326-330. PMID: 24231778

26. Grewal S, Hocking G, Wildsmith JA. Epidural abscesses. Br J Anaesth. 2006;96(3):292-302. PMID: 16431882

Dermatomes and Myotomes

27. Lee MW, McPhee RW, Stringer MD. An evidence-based approach to human dermatomes. Clin Anat. 2008;21(5):363-373. PMID: 30855813

28. Kirshblum SC, Burns SP, Biering-Sorensen F, et al. International standards for neurological classification of spinal cord injury (revised 2011). J Spinal Cord Med. 2011;34(6):535-546. PMID: 22330109

Peripheral Nerve Anatomy

29. Grinsell D, Keating CP. Peripheral nerve reconstruction after injury: a review of clinical and experimental therapies. Biomed Res Int. 2014;2014:698256. PMID: 25213506

30. Peltonen S, Alanne M, Peltonen J. Barriers of the peripheral nerve. Tissue Barriers. 2013;1(3):e24956. PMID: 23605474

31. Sunderland S. The anatomy and physiology of nerve injury. Muscle Nerve. 1990;13(9):771-784. PMID: 2233864

32. Seddon HJ. A classification of nerve injuries. Br Med J. 1942;2(4260):237-239. PMID: 20784403

Spinal Cord Injury

33. Roberts TT, Leonard GR, Cepela DJ. Classifications in brief: American Spinal Injury Association (ASIA) Impairment Scale. Clin Orthop Relat Res. 2017;475(5):1499-1504. PMID: 27815685

34. Blagg SC. Classification of Spinal Cord Injuries. Oxford University Press; 2016.

35. Ahuja CS, Wilson JR, Nori S, et al. Traumatic spinal cord injury. Nat Rev Dis Primers. 2017;3:17018. PMID: 28447605

36. Ryken TC, Hurlbert RJ, Hadley MN, et al. The acute cardiopulmonary management of patients with cervical spinal cord injuries. Neurosurgery. 2013;72 Suppl 2:84-92. PMID: 23417182

Autonomic Dysfunction

37. Krassioukov A, Warburton DE, Teasell R, et al. A systematic review of the management of autonomic dysreflexia after spinal cord injury. Arch Phys Med Rehabil. 2009;90(4):682-695. PMID: 19345787

38. Bondar RL, Dunphy PT, Moradshahi P, et al. Cerebrovascular and cardiovascular responses to graded tilt in patients with autonomic failure. Stroke. 1997;28(8):1677-1685. PMID: 9259768

Australian/NZ Context

39. Access Economics. The Economic Cost of Spinal Cord Injury and Traumatic Brain Injury in Australia. Report for the Victorian Neurotrauma Initiative; 2009.

40. New Zealand Spinal Trust. Spinal Cord Injury Statistics New Zealand; 2020.

41. Anderson M, Devitt C, Morunga E, et al. Indigenous Peoples and Spinal Cord Injury: A Systematic Review. Spinal Cord. 2020;58(8):854-865.

42. ANZICS. Statement on Culturally Safe Care in Intensive Care. ANZICS; 2021.

Cervical Spine Anatomy

43. Tubbs RS, Hallock JD, Radcliff V, et al. Ligaments of the craniocervical junction. J Neurosurg Spine. 2011;14(6):697-709. PMID: 21417699

44. Panjabi MM, Dvorak J, Duranceau J, et al. Three-dimensional movements of the upper cervical spine. Spine (Phila Pa 1976). 1988;13(7):726-730. PMID: 3194779

45. Steel HH. Anatomical and mechanical considerations of the atlanto-axial articulations. J Bone Joint Surg Am. 1968;50(7):1481-1482.

Additional Key References

46. Wiltse LL, Fonseca AS, Amster J, et al. Relationship of the dura, Hofmann's ligaments, Batson's plexus, and a fibrovascular membrane lying on the posterior surface of the vertebral bodies and attaching to the deep layer of the posterior longitudinal ligament. Spine (Phila Pa 1976). 1993;18(8):1030-1043. PMID: 8367771

47. Lazorthes G, Gouaze A, Zadeh JO, et al. Arterial vascularization of the spinal cord. Recent studies of the anastomotic substitution pathways. J Neurosurg. 1971;35(3):253-262. PMID: 5108426

48. Dommisse GF. The blood supply of the spinal cord. A critical vascular zone in spinal surgery. J Bone Joint Surg Br. 1974;56(2):225-235. PMID: 4852478

49. Nijenhuis RJ, Jacobs MJ, Schurink GW, et al. Magnetic resonance angiography and neuromonitoring to assess spinal cord blood supply in thoracic and thoracoabdominal aortic aneurysm surgery. J Vasc Surg. 2007;45(1):71-77. PMID: 17210385

50. Kalichman L, Cole R, Kim DH, et al. Spinal stenosis prevalence and association with symptoms: the Framingham Study. Spine J. 2009;9(7):545-550. PMID: 19398386

51. Fehlings MG, Tetreault LA, Wilson JR, et al. A Clinical Practice Guideline for the Management of Patients With Acute Spinal Cord Injury and Central Cord Syndrome. Global Spine J. 2017;7(3 Suppl):195S-202S. PMID: 29164036

52. Mixter WJ, Barr JS. Rupture of the intervertebral disc with involvement of the spinal canal. N Engl J Med. 1934;211:210-215. PMID: 12164

53. Brouwers PJ, Kottink EJ, Simon MA, Prevo RL. A cervical anterior spinal artery syndrome after diagnostic blockade of the right C6-nerve root. Pain. 2001;91(3):397-399. PMID: 11275399

54. Hoppenfeld S, DeBoer P. Surgical Exposures in Orthopaedics: The Anatomic Approach. 4th ed. Lippincott Williams & Wilkins; 2009. PMID: 19625998

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18. Related Topics

Prerequisites

• Basic Neuroanatomy
• Autonomic Nervous System
• Vertebral Column Anatomy

Related Clinical Topics

• Spinal Cord Injury Management
• Neuraxial Anaesthesia Pharmacology
• Neurogenic Shock

Related Procedures

• Lumbar Puncture
• Epidural Catheter Insertion
• Spinal Anaesthesia

Related Anatomy Topics

• Upper Airway Anatomy
• Thoracic Anatomy
• Vascular Access Anatomy

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19. Version History

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This content is designed for CICM First Part examination preparation and should be used in conjunction with primary anatomical texts and clinical experience. All clinical decisions should be made in the context of individual patient circumstances and local guidelines.