Thyroid Nodules & Goitre

1. Clinical Overview

Summary

Thyroid nodules are discrete lesions within the thyroid gland that are palpably or radiologically distinct from surrounding thyroid parenchyma. They represent one of the most common endocrine disorders, with a prevalence that increases with age and is higher in women than men. [1,2] While the vast majority of thyroid nodules are benign (> 95%), the primary clinical challenge lies in identifying the small subset that harbor malignancy without subjecting all patients to unnecessary invasive procedures. [3]

The detection of thyroid nodules has increased dramatically over the past three decades, primarily due to the widespread use of high-resolution imaging modalities such as ultrasound, CT, and MRI performed for unrelated indications. These "thyroid incidentalomas" now account for the majority of newly diagnosed nodules. [4] Despite this increased detection, thyroid cancer mortality has remained stable, suggesting that many detected nodules represent indolent disease that may never have become clinically significant. [5]

The cornerstone of modern thyroid nodule management is risk stratification using a combination of clinical features, ultrasound characteristics, and when appropriate, fine needle aspiration (FNA) cytology. This approach, codified in guidelines from major endocrine societies, aims to balance the need for cancer detection against the harms of overdiagnosis and overtreatment. [6,7]

Key Facts

• Prevalence: Palpable thyroid nodules occur in 4-7% of the adult population, but ultrasound detection reveals nodules in 19-68% of randomly selected individuals, with higher rates in women and with increasing age. [1,2]
• Malignancy risk: Only 5-15% of thyroid nodules are malignant, with the risk varying based on patient demographics and nodule characteristics. [8]
• Incidentalomas: Most thyroid nodules are now discovered incidentally on imaging studies (CT, MRI, PET) performed for unrelated conditions. [4]
• Functional status: The majority of thyroid nodules are "cold" (non-functioning) and do not affect thyroid hormone production. Functioning "hot" nodules that suppress TSH carry a very low risk of malignancy (less than 1%). [9]
• Goitre: Defined as thyroid gland enlargement, which can be diffuse (Graves' disease, Hashimoto's thyroiditis) or nodular (multinodular goitre). Retrosternal extension occurs in 5-20% of multinodular goitres and may cause compressive symptoms. [10]

Clinical Pearls

Pemberton's Sign: This classic bedside test assesses for retrosternal goitre with thoracic inlet obstruction. The patient is asked to raise both arms above the head (touching the ears) and maintain this position for one minute.

• Positive findings: Facial plethora (congestion), venous engorgement, cyanosis, or inspiratory stridor within 60 seconds
• Mechanism: The enlarged thyroid gland is lifted superiorly into the thoracic inlet, compressing the internal jugular veins and superior vena cava, producing symptoms of venous obstruction ("cork in a bottle" phenomenon)
• Clinical significance: A positive sign indicates significant retrosternal extension and potential for airway compromise, often warranting surgical evaluation. [11]

The "Follicular Lesion" Diagnostic Dilemma: Fine needle aspiration cytology cannot reliably distinguish between follicular adenoma (benign) and follicular carcinoma (malignant). This is because the defining histologic feature of follicular carcinoma is capsular or vascular invasion, which requires examination of the entire nodule architecture—impossible to assess on cytology specimens that provide only individual cells or small tissue fragments. [12]

• Implication: All nodules with follicular neoplasm cytology (Bethesda Category IV/Thy3f) require diagnostic surgical excision (typically hemithyroidectomy) to establish definitive histology
• Prevalence: Only 15-30% of follicular neoplasms prove malignant on final histology, meaning 70-85% of patients undergo surgery for ultimately benign disease [13]
• Molecular testing: BRAF, RAS, RET/PTC, and PAX8/PPARγ mutation analysis may help refine risk in indeterminate nodules, potentially reducing unnecessary surgery. [14]

---

2. Epidemiology

Prevalence and Incidence

Thyroid nodules are extraordinarily common, with prevalence varying based on detection method:

Incidence: The apparent incidence of thyroid cancer has increased dramatically over the past 30 years, rising from 4.9 per 100,000 in 1975 to 14.3 per 100,000 in 2009, representing a nearly 3-fold increase. This increase is almost entirely attributable to small papillary thyroid cancers (less than 2cm), consistent with increased detection rather than true disease increase. [5,16]

Demographic Patterns

Age:

• Prevalence increases with age, with approximately 1% increase per year of life
• Peak incidence occurs in the 5th-6th decades
• Nodules in children and adolescents are less common but carry higher malignancy risk (22-26%) compared to adults (5-15%) [17]

Sex:

• Female to male ratio: 4:1 for benign nodules
• Women are more likely to develop nodules, but nodules in men have higher malignancy risk (relative risk 1.5-2.0) [18]

Geography:

• Higher prevalence in iodine-deficient regions (endemic goitre)
• Areas with adequate iodine supplementation show lower rates of multinodular goitre but stable prevalence of solitary nodules [19]

Risk Factors for Thyroid Nodules

General Population:

• Female sex
• Increasing age
• Iodine deficiency
• Family history of thyroid disease
• Prior head and neck radiation exposure

Environmental Exposures:

• Radiation exposure (diagnostic, therapeutic, or environmental)
• Iodine deficiency or excess
• Certain medications (lithium, amiodarone)

Risk Factors for Malignancy in a Thyroid Nodule

Genetic Syndromes Associated with Thyroid Cancer:

• Multiple Endocrine Neoplasia Type 2 (MEN2): Medullary thyroid cancer (nearly 100% penetrance with RET mutations)
• Familial Adenomatous Polyposis (FAP): Increased risk of papillary thyroid cancer (2% prevalence)
• Cowden Syndrome (PTEN mutations): Follicular thyroid cancer risk
• Carney Complex: Follicular thyroid neoplasms
• Werner Syndrome: Follicular and papillary thyroid cancer [21]

---

3. Pathophysiology

Normal Thyroid Anatomy and Physiology

The thyroid gland consists of two lobes connected by an isthmus, located anterior to the trachea at the level of C5-T1 vertebrae. The functional unit is the thyroid follicle, comprising follicular epithelial cells surrounding a colloid-filled lumen. Parafollicular C-cells, which secrete calcitonin, are interspersed between follicles. [23]

Mechanisms of Nodule Formation

Nodular Hyperplasia:

• Most common mechanism
• Polyclonal proliferation of follicular cells in response to various stimuli (TSH, growth factors, iodine deficiency)
• Results in adenomatous or colloid nodules
• Molecular basis: Accumulation of somatic mutations in genes regulating growth (TSH receptor, Gαs protein) [24]

Neoplastic Transformation:

• Monoclonal proliferation from genetic alterations
• Benign neoplasms (follicular adenoma) vs malignant (carcinoma)
• Key molecular pathways:
  • "MAPK pathway (BRAF, RAS, RET/PTC mutations): Papillary thyroid cancer"
  • "PI3K/AKT pathway (PTEN, PIK3CA): Follicular thyroid cancer"
  • "TP53, CTNNB1 (β-catenin): Poorly differentiated and anaplastic cancer [14,25]"

Inflammatory/Autoimmune:

• Hashimoto's thyroiditis: Lymphocytic infiltration creating pseudonodular appearance
• Subacute thyroiditis: Painful inflammatory nodules
• Riedel's thyroiditis: Rare fibrous replacement mimicking malignancy

Cystic Degeneration:

• Hemorrhage, necrosis, or colloid accumulation within nodules
• Pure cysts (less than 2% of nodules) are almost always benign
• Complex cystic-solid nodules require same evaluation as solid nodules [26]

Types of Thyroid Nodules

Benign Nodules (> 90% of all nodules)

1. Colloid Nodules (Adenomatous Nodules)

• Most common type
• Result from hyperplastic follicles with abundant colloid
• Typically develop in multinodular goitres
• No malignant potential

2. Follicular Adenoma

• True benign neoplasm (monoclonal)
• Encapsulated proliferation of follicular cells
• Cannot be distinguished from follicular carcinoma by cytology alone
• Requires histologic examination to exclude capsular/vascular invasion

3. Cysts

• Simple cysts: Fluid-filled, benign
• Complex cysts: Mixed solid-cystic, require same evaluation as solid nodules
• May result from degeneration/hemorrhage of adenomas or carcinomas

4. Inflammatory Nodules

• Hashimoto's thyroiditis: Pseudonodules from lymphocytic infiltration
• Subacute (de Quervain's) thyroiditis: Painful, tender, typically self-limited
• Acute suppurative thyroiditis: Rare bacterial infection

Malignant Nodules (5-15% of nodules)

1. Papillary Thyroid Carcinoma (PTC) - 80-85% of thyroid cancers

• Most common thyroid malignancy
• Peak incidence: 30-50 years; F:M = 3:1
• Pathology: Papillary architecture, "Orphan Annie eye" nuclei (ground-glass appearance), psammoma bodies (calcifications)
• Molecular: BRAF V600E mutation (40-45%), RET/PTC rearrangements (20%), RAS mutations (10-15%)
• Spread: Primarily lymphatic (50-70% have lymph node metastases at diagnosis)
• Prognosis: Excellent; > 95% 10-year survival for localized disease [27]

2. Follicular Thyroid Carcinoma (FTC) - 10-15% of thyroid cancers

• Second most common
• Peak incidence: 40-60 years; more common in iodine-deficient areas
• Pathology: Follicular architecture with capsular or vascular invasion (defines malignancy)
• Molecular: RAS mutations (40-50%), PAX8/PPARγ rearrangement (30-35%)
• Spread: Hematogenous (bone, lung metastases)
• Prognosis: Good; 85-90% 10-year survival; worse with vascular invasion [28]

3. Medullary Thyroid Carcinoma (MTC) - 3-5% of thyroid cancers

• Arises from parafollicular C-cells
• 75% sporadic, 25% hereditary (MEN2A, MEN2B, familial MTC)
• Pathology: Sheets of cells, amyloid deposition
• Molecular: RET proto-oncogene mutations (hereditary cases; 50% sporadic cases)
• Biomarker: Calcitonin production (diagnostic and monitoring)
• Spread: Early lymphatic and distant metastases
• Prognosis: Intermediate; 70-80% 10-year survival; depends on stage at diagnosis [29]

4. Anaplastic Thyroid Carcinoma (ATC) - 1-2% of thyroid cancers

• Highly aggressive undifferentiated carcinoma
• Peak incidence: > 60 years
• Pathology: Undifferentiated pleomorphic cells
• Molecular: TP53 mutations, BRAF mutations, often with loss of differentiation markers
• Presentation: Rapidly enlarging neck mass, hoarseness, dysphagia, dyspnea
• Prognosis: Dismal; median survival 3-5 months; most die within 1 year [30]

5. Thyroid Lymphoma - 1-2% of thyroid malignancies

• Usually non-Hodgkin B-cell lymphoma (MALT or diffuse large B-cell)
• Strong association with Hashimoto's thyroiditis (40-80x increased risk)
• Presentation: Rapidly enlarging goitre in patient with chronic thyroiditis
• Treatment: Chemotherapy ± radiotherapy (not surgery)
• Prognosis: Variable; depends on histologic subtype and stage [31]

Molecular Pathogenesis

Exam Detail: MAPK Pathway Activation (Papillary Thyroid Cancer):

The MAPK (mitogen-activated protein kinase) pathway is critical for cell proliferation, differentiation, and survival. In papillary thyroid cancer, this pathway is constitutively activated through several mechanisms:

1. BRAF V600E mutation (40-45% of PTC):

   • Most common genetic alteration in PTC
   • Point mutation causes substitution of glutamic acid for valine at position 600
   • Results in constitutive BRAF kinase activity
   • Associated with more aggressive tumor behavior, extrathyroidal extension, and higher recurrence risk
   • Target for therapy: BRAF inhibitors (vemurafenib, dabrafenib) in advanced disease [14]

2. RET/PTC rearrangements (20-30% of PTC):

   • Chromosomal rearrangements fusing RET tyrosine kinase domain with various partner genes
   • Most common: RET/PTC1 (CCDC6-RET) and RET/PTC3 (NCOA4-RET)
   • Associated with radiation-induced thyroid cancer
   • More common in younger patients and those with classic papillary architecture

3. RAS mutations (10-15% of PTC, higher in follicular variant):

   • NRAS, HRAS, KRAS mutations
   • Activates both MAPK and PI3K/AKT pathways
   • Associated with follicular variant of PTC and follicular thyroid carcinoma
   • Generally associated with more favorable prognosis than BRAF mutations

PI3K/AKT Pathway (Follicular Thyroid Cancer):

The PI3K/AKT pathway regulates cell growth, survival, and metabolism. Alterations include:

1. PIK3CA mutations: Activating mutations in PI3K catalytic subunit
2. PTEN loss: Tumor suppressor gene; loss leads to pathway activation
3. AKT activation: Increased phosphorylation and activity
4. PAX8/PPARγ rearrangement: Fusion of PAX8 (transcription factor) with PPARγ (nuclear receptor); found in 30-35% of follicular carcinomas [25]

RET Proto-oncogene (Medullary Thyroid Cancer):

• Germline RET mutations: Nearly 100% penetrance for MTC in MEN2
  • "MEN2A: Codon 634 mutations (most common)"
  • "MEN2B: Codon 918 mutations (most aggressive)"
  • "Familial MTC: Various codons"
• Somatic RET mutations: Found in ~50% of sporadic MTC
• Clinical application: Prophylactic thyroidectomy in RET mutation carriers
• Targeted therapy: RET inhibitors (selpercatinib, pralsetinib) for advanced MTC [29]

Progression to Undifferentiated Cancer:

Anaplastic thyroid cancer may arise from dedifferentiation of well-differentiated thyroid cancer through accumulation of additional mutations:

• TP53 mutations (60-80% of ATC)
• β-catenin/CTNNB1 mutations
• TERT promoter mutations
• Loss of thyroid-specific transcription factors (PAX8, NKX2-1) [30]

---

4. Clinical Presentation

Symptoms

Most thyroid nodules are asymptomatic and discovered incidentally. When symptoms occur, they may include:

Local Symptoms (Mass Effect):

• Visible or palpable neck lump (most common presenting complaint)
• Neck pressure or fullness
• Dysphagia (difficulty swallowing) - from esophageal compression
• Dyspnea or positional breathlessness - from tracheal compression
• Choking sensation
• Globus sensation (lump in throat)

Compressive Symptoms (Goitre):

• Orthopnea (breathlessness when lying flat) - suggests significant retrosternal extension
• Stridor - indicates critical tracheal narrowing (less than 5mm lumen); medical emergency
• Superior vena cava syndrome - rare; from massive retrosternal goitre

Symptoms Suggesting Malignancy:

• Hoarseness or voice change - suggests recurrent laryngeal nerve involvement (high suspicion for cancer)
• Rapidly enlarging mass - concerning for anaplastic cancer or lymphoma
• Persistent cervical lymphadenopathy
• Pain - unusual; may indicate hemorrhage into nodule or rapid growth

Functional Symptoms:

• Hyperthyroidism (rare): Palpitations, tremor, weight loss, heat intolerance - from autonomous functioning nodule (toxic adenoma) or toxic multinodular goitre
• Hypothyroidism: Fatigue, weight gain, cold intolerance - from chronic thyroiditis with nodules

Constitutional Symptoms (Advanced Malignancy):

• Weight loss
• Fatigue
• Bone pain (skeletal metastases from follicular cancer)
• Hemoptysis (pulmonary metastases)

Signs

General Inspection:

• Visible neck asymmetry or swelling
• Observe swallowing - thyroid masses move upward with swallowing (attached to larynx via pretracheal fascia)
• Cachexia - advanced malignancy

Palpation Characteristics:

Examination Technique:

• Position: Examiner stands behind seated patient
• Palpation: Use both hands to palpate thyroid lobes and isthmus
• Swallowing: Ask patient to swallow (provide water) - thyroid masses move upward
• Tongue protrusion: Thyroglossal cyst moves upward with tongue protrusion (thyroid nodules do not)

Associated Findings:

Lymphadenopathy:

• Cervical lymph nodes (levels II-VI) - suggests papillary thyroid cancer
• Level VI (central compartment) - first echelon for thyroid drainage
• Levels II-IV (lateral neck) - secondary spread
• Hard, fixed, matted nodes highly suspicious

Vocal Cord Assessment:

• Hoarseness - may indicate recurrent laryngeal nerve palsy
• Laryngoscopy essential if voice changes present (surgical planning)

Vascular Signs:

• Venous engorgement - retrosternal goitre with venous compression
• Pemberton's sign (see Clinical Pearls) - sensitive for retrosternal extension

Signs of Thyroid Dysfunction:

Hyperthyroidism:

• Tachycardia, atrial fibrillation
• Tremor, hyperreflexia
• Warm, moist skin
• Thyroid bruit (Graves' disease)

Hypothyroidism:

• Bradycardia
• Delayed relaxation of ankle reflexes
• Dry, cool skin
• Periorbital edema

Special Examination Findings:

Pemberton's Sign (detailed in Clinical Pearls):

• Patient raises both arms above head for 60 seconds
• Positive: Facial plethora, venous congestion, stridor
• Indicates thoracic inlet obstruction from retrosternal goitre [11]

---

5. Differential Diagnosis

When evaluating a neck mass, consider:

Primary Thyroid Pathology

1. Benign thyroid nodule (most common)

   • Colloid nodule, follicular adenoma, cyst
   • Soft, mobile, moves with swallowing

2. Multinodular goitre

   • Multiple palpable nodules
   • May have retrosternal extension

3. Thyroid cancer

   • Hard, fixed, associated lymphadenopathy
   • Hoarseness (RLN involvement)

4. Thyroiditis

   • Hashimoto's: Firm, diffusely enlarged, may have pseudonodules
   • Subacute (de Quervain's): Painful, tender, systemic symptoms
   • Acute suppurative: Rare; fever, severe pain, abscess

Non-Thyroid Neck Masses

Must-Not-Miss Diagnoses

1. Thyroid cancer - especially in high-risk patients (radiation exposure, family history, concerning features)
2. Anaplastic thyroid carcinoma - rapidly enlarging mass, airway compression, elderly patient
3. Thyroid lymphoma - rapid enlargement in patient with chronic Hashimoto's thyroiditis
4. Retrosternal goitre with airway compromise - positional dyspnea, stridor, positive Pemberton's sign

---

6. Investigations

The evaluation of thyroid nodules follows a systematic, risk-stratified approach.

Initial Assessment

1. Serum TSH (Thyroid-Stimulating Hormone)

• First and most important test [6,7]
• Determines functional status and guides further investigation

Rationale: Hyperfunctioning ("hot") nodules that suppress TSH carry very low malignancy risk (less than 1%), making radionuclide imaging more appropriate than immediate FNA. [9]

2. Thyroid Ultrasound

• Gold standard imaging modality for thyroid nodule characterization
• Superior to clinical examination in detecting nodules and assessing characteristics
• Should evaluate:
  • Nodule composition (solid, cystic, mixed)
  • Echogenicity (hypoechoic, isoechoic, hyperechoic)
  • Margins (smooth, irregular, infiltrative)
  • Calcifications (micro vs macro)
  • Vascularity
  • Cervical lymph nodes

Ultrasound Risk Stratification Systems

Multiple classification systems exist; the most widely used are:

British Thyroid Association (BTA) U-Classification:

American College of Radiology (ACR) TI-RADS (Thyroid Imaging Reporting and Data System):

• Points assigned for suspicious features:
  • Composition (solid > cystic)
  • Echogenicity (hypoechoic)
  • Shape (taller than wide)
  • Margins (irregular, infiltrative)
  • Echogenic foci (microcalcifications)
• Total score determines FNA size threshold [32]

Ultrasound Features Suggesting Malignancy:

Benign Ultrasound Features:

• Purely cystic
• Spongiform (> 50% cystic composition with multiple small cysts)
• Peripheral halo (smooth, regular)
• Comet-tail artifacts (colloid)
• Hyperechoic or isoechoic
• Smooth margins

Fine Needle Aspiration (FNA) Cytology

Indications for FNA: [6,7]

• Nodules ≥1cm with suspicious ultrasound features (U3-U5)
• Nodules less than 1cm if:
  • High clinical suspicion (radiation exposure, family history)
  • Suspicious lymph nodes
  • Extrathyroidal extension on ultrasound
• Nodules with documented growth (> 20% increase in at least 2 dimensions)

FNA Technique:

• Typically performed under ultrasound guidance (higher diagnostic yield than palpation-guided)
• 25-27 gauge needle
• Multiple passes (2-4) to ensure adequate cellularity
• On-site cytology assessment improves adequacy rates

Bethesda System for Reporting Thyroid Cytopathology (2017):

British Thy Classification (equivalent):

• Thy1 = Bethesda I
• Thy2 = Bethesda II
• Thy3a = Bethesda III
• Thy3f = Bethesda IV
• Thy4 = Bethesda V
• Thy5 = Bethesda VI [12]

Exam Detail: The Follicular Neoplasm Dilemma:

Follicular adenoma (benign) and follicular carcinoma (malignant) have identical cytologic appearances. Both show:

• Microfollicular architecture
• Scant or absent colloid
• Uniform follicular cells

The ONLY distinguishing feature is capsular or vascular invasion, which requires:

• Examination of the entire tumor capsule
• Assessment of vascular structures
• Histologic sections (not cytology)

Therefore, all Bethesda IV/Thy3f nodules require diagnostic surgical excision (hemithyroidectomy) to:

1. Remove nodule intact with capsule
2. Perform complete histologic examination
3. Assess for invasion (definitive diagnosis)

Outcome: Only 15-30% prove malignant on final histology, meaning 70-85% undergo surgery for benign disease. This has led to interest in molecular testing to refine risk. [13]

Molecular Testing

Indications:

• Bethesda III (AUS/FLUS) or IV (Follicular Neoplasm) cytology
• May help avoid diagnostic surgery for benign nodules
• Most useful when pretest probability of malignancy is intermediate

Common Gene Panels:

1. Afirma Gene Expression Classifier

   • Measures expression of 167 genes
   • "Benign" result has high negative predictive value (NPV 95%)
   • Can avoid surgery in ~50% of Bethesda III/IV nodules

2. ThyroSeq Genomic Classifier

   • Next-generation sequencing panel
   • Detects point mutations and gene fusions
   • Provides malignancy risk estimate (0-100%)

3. Common Mutations Assessed:

   • BRAF V600E (specific for PTC; 99% PPV)
   • RAS (NRAS, HRAS, KRAS) - intermediate risk
   • RET/PTC rearrangements - PTC
   • PAX8/PPARγ - follicular neoplasms
   • TERT promoter - aggressive behavior [14,33]

Limitations:

• Cost
• Not universally available
• Cannot completely exclude malignancy
• Uncertain significance of some mutations

Additional Investigations

Calcitonin (Controversial):

• Indication: Suspected medullary thyroid cancer
  • Family history of MTC or MEN2
  • Nodule with high serum calcitonin
• Controversy: Routine screening calcitonin in all nodules is NOT recommended by most guidelines (low prevalence, cost, false positives) but is practiced in some European countries [6,7]

Thyroglobulin:

• NOT useful for diagnosing primary thyroid cancer
• Used for monitoring after thyroidectomy for thyroid cancer

Anti-thyroid Antibodies:

• Anti-TPO (thyroid peroxidase) antibodies
• Anti-thyroglobulin antibodies
• Useful if TSH elevated (diagnose Hashimoto's thyroiditis)
• Presence does NOT exclude malignancy

Radionuclide Thyroid Scan (Technetium-99m or Iodine-123):

Indications:

• Low/suppressed TSH (suspected toxic nodule or toxic multinodular goitre)

Interpretation:

Limitations:

• Cannot distinguish benign from malignant cold nodules
• Largely replaced by ultrasound for nodule characterization
• Still useful for mapping functional status in hyperthyroidism [9]

Cross-Sectional Imaging (CT/MRI):

Indications:

• Large goitres with retrosternal extension
• Assess tracheal deviation/compression
• Pre-operative planning for substernal goitre surgery
• Staging of known thyroid cancer (assess extrathyroidal extension, lymph nodes)

Findings:

• Tracheal deviation or compression
• Extent of retrosternal extension
• Relationship to great vessels
• Lymphadenopathy

Important: Use non-contrast CT when possible to avoid iodine load (delays radioiodine therapy if cancer diagnosed)

PET-CT (18F-FDG):

• NOT for routine nodule evaluation
• Thyroid incidentalomas on PET (SUV > 10) have ~35% malignancy risk - require evaluation
• Used for staging/surveillance of aggressive thyroid cancers or thyroid cancer metastases that have lost iodine avidity

Laryngoscopy (Flexible Nasendoscopy):

Indications:

• Any voice change or hoarseness
• Pre-operative assessment before thyroid surgery
• Large goitres with compressive symptoms

Purpose:

• Assess vocal cord mobility (detect RLN palsy)
• Document baseline vocal cord function
• Essential for informed consent if surgery planned

---

7. Classification and Staging

Thyroid Cancer TNM Staging (AJCC 8th Edition, 2017)

Important change in 8th edition: Age cutoff changed from 45 to 55 years, reflecting improved outcomes and more accurate risk stratification.

For Papillary, Follicular, Poorly Differentiated, Hürthle Cell Carcinomas:

Primary Tumor (T):

• TX: Primary tumor cannot be assessed
• T0: No evidence of primary tumor
• T1: Tumor ≤2cm, limited to thyroid
  • T1 a: ≤1cm
  • T1 b: > 1cm but ≤2cm
• T2: Tumor > 2cm but ≤4cm, limited to thyroid
• T3: Tumor > 4cm limited to thyroid OR minimal extrathyroidal extension (e.g., into strap muscles)
  • T3 a: > 4cm limited to thyroid
  • T3 b: Gross extrathyroidal extension into strap muscles
• T4: Advanced disease
  • T4 a: Extends beyond thyroid capsule to invade subcutaneous soft tissues, larynx, trachea, esophagus, or recurrent laryngeal nerve
  • T4 b: Invades prevertebral fascia or encases carotid artery or mediastinal vessels

Regional Lymph Nodes (N):

• NX: Regional nodes cannot be assessed
• N0: No regional lymph node metastasis
• N0a: ≥1 cytologically or histologically confirmed benign lymph nodes
• N0b: No radiologic or clinical evidence of locoregional lymph node metastasis
• N1: Regional lymph node metastasis
  • N1 a: Metastasis to level VI or VII (central compartment)
  • N1 b: Metastasis to lateral cervical or superior mediastinal nodes

Distant Metastasis (M):

• M0: No distant metastasis
• M1: Distant metastasis (lung, bone, brain, liver)

Stage Grouping for Papillary/Follicular Thyroid Cancer:

Age less than 55 years:

• Stage I: Any T, Any N, M0
• Stage II: Any T, Any N, M1

Age ≥55 years:

• Stage I: T1, N0/NX, M0 or T2, N0/NX, M0
• Stage II: T1-T2, N1, M0 or T3, Any N, M0
• Stage III: T4a, Any N, M0
• Stage IVA: T4b, Any N, M0
• Stage IVB: Any T, Any N, M1

Medullary Thyroid Carcinoma Staging:

• Uses same TNM definitions but ALL age groups use same stage grouping (age not a factor)

Anaplastic Thyroid Carcinoma:

• ALL anaplastic cancers are classified as Stage IV (inherently aggressive)
  • "IVA: Intrathyroidal"
  • "IVB: Extrathyroidal"
  • "IVC: Distant metastases [27]"

Risk Stratification Systems

American Thyroid Association (ATA) Risk Stratification (for papillary/follicular cancer):

---

8. Management

The management of thyroid nodules is highly individualized, based on clinical, sonographic, and cytologic risk stratification.

Management Algorithm

                   THYROID NODULE DISCOVERED
                            ↓
                     MEASURE SERUM TSH
                            ↓
         ┌──────────────────┴──────────────────┐
         ↓                                     ↓
    TSH LOW/SUPPRESSED                   TSH NORMAL/HIGH
    (Hyperthyroid)                       (Euthyroid)
         ↓                                     ↓
   RADIONUCLIDE SCAN               THYROID ULTRASOUND
   (Tc-99m or I-123)               (Assign U-Score/TI-RADS)
         ↓                                     ↓
    ┌────┴────┐                    ┌──────────┴──────────┐
    ↓         ↓                    ↓                     ↓
  HOT       COLD                U2 (Benign)        U3/U4/U5
  NODULE    NODULE                 ↓                     ↓
    ↓         ↓                 OBSERVE              FNA IF SIZE
 TREAT    ULTRASOUND          (6-12mo U/S)         THRESHOLD MET
 HYPER-   + FNA                   ↓                     ↓
 THYROID                      No growth:        BETHESDA CATEGORY
    ↓                         Continue             (Thy grade)
 RAI-131 or                   surveillance              ↓
 SURGERY                                     ┌───────────┴────────┬─────────┐
                                            ↓          ↓          ↓         ↓
                                         Thy2      Thy3a/3f    Thy4/5    Thy1
                                       (Benign)   (Indeter.)  (Susp/    (Non-
                                          ↓           ↓        Malig)    diagn)
                                      DISCHARGE   REPEAT FNA     ↓         ↓
                                      (Annual     or MOLEC.   SURGERY   REPEAT
                                       U/S if     TESTING or            FNA
                                       > 1cm)      SURGERY
                                                     ↓
                                              HEMI or TOTAL
                                              THYROIDECTOMY
                                                     ↓
                                              HISTOLOGY
                                                  ↓
                                        ┌─────────┴─────────┐
                                        ↓                   ↓
                                    BENIGN              MALIGNANT
                                        ↓                   ↓
                                   DISCHARGE          COMPLETION
                                (If hemithyroid       THYROIDECTOMY
                                 sufficient)         (if indicated)
                                                          +
                                                    RAI ABLATION
                                                   (if indicated)

Conservative Management

Observation (Active Surveillance):

Indications:

• Benign cytology (Bethesda II/Thy2)
• Very small papillary microcarcinomas (less than 1cm) in selected patients
• Benign ultrasound features (U2)
• Patient preference in low-risk nodules

Surveillance Protocol: [6,7]

• Benign nodules:

  • Repeat ultrasound at 6-12 months
  • If stable, repeat every 12-24 months for 3-5 years
  • Can extend intervals or discontinue if stable

• Papillary microcarcinoma (active surveillance protocol):

  • Japanese studies demonstrate safety of observation for low-risk microcarcinomas
  • Ultrasound every 6 months for first 2 years, then annually
  • "Surgery if: > 3mm growth, lymph node metastases, extrathyroidal extension, patient preference [34]"

Indications for Repeat FNA:

• Nodule growth (> 20% increase in 2 dimensions, with minimum 2mm increase)
• Development of suspicious ultrasound features
• Non-diagnostic initial FNA (Bethesda I)
• Indeterminate cytology (Bethesda III) if molecular testing not performed

TSH Suppression Therapy:

• NOT recommended for benign nodules in iodine-sufficient areas
• No proven benefit in reducing nodule size
• Risks: Atrial fibrillation, osteoporosis (especially postmenopausal women)
• May consider in iodine-deficient areas or growing nodules despite benign cytology [6]

Medical Management

Hyperthyroidism from Toxic Nodule/Goitre:

1. Anti-thyroid Drugs (ATDs):

• Methimazole (preferred; 10-30mg daily) or Propylthiouracil (PTU; 100-300mg daily)
• Limitation: Only temporary control; nodule autonomy persists
• Role: Bridge to definitive therapy (RAI or surgery) or in poor surgical candidates

2. Beta-Blockers:

• Propranolol 20-40mg QID or Atenolol 25-100mg daily
• Symptom control (palpitations, tremor)
• Not definitive therapy

Definitive Treatment for Toxic Nodules:

• Radioactive iodine (RAI-131) - preferred for most patients
• Surgery - if large nodule, compressive symptoms, or patient preference

Surgical Management

Indications for Surgery:

Diagnostic (Benign or Indeterminate Cytology):

• Bethesda IV (Follicular neoplasm/Thy3f) - cannot exclude cancer without histology
• Large nodules causing compressive symptoms
• Retrosternal extension
• Cosmetic concerns (patient preference)

Therapeutic (Malignant or Suspicious Cytology):

• Bethesda V (Suspicious for malignancy)
• Bethesda VI (Malignant)
• Bethesda III with high-risk molecular markers

Other Indications:

• Toxic nodule (alternative to RAI)
• Compressive symptoms (dysphagia, dyspnea, stridor)
• Rapid growth despite benign cytology
• Patient preference

Surgical Options:

1. Diagnostic Hemithyroidectomy (Thyroid Lobectomy)

Indications:

• Bethesda III/IV cytology (follicular neoplasm)
• Small low-risk papillary cancers (less than 2cm, no extrathyroidal extension, no lymph node metastases)
• Single lobe involvement
• Toxic adenoma (alternative to RAI)

Advantages:

• Lower complication risk (RLN injury ~1%, hypoparathyroidism less than 1%)
• Preserves thyroid function in ~80% (no lifelong levothyroxine needed)
• Can perform completion thyroidectomy if cancer diagnosed and total thyroidectomy indicated

Disadvantages:

• If cancer diagnosed requiring total thyroidectomy, need second operation (completion thyroidectomy has higher complication risk)
• Cannot use radioiodine ablation/therapy
• Cannot monitor with serum thyroglobulin

2. Total Thyroidectomy

Indications:

• Malignant cytology (Bethesda VI)
• Tumor > 4cm
• Bilateral thyroid nodules requiring surgery
• Extrathyroidal extension
• Lymph node metastases
• Distant metastases
• Family history or radiation exposure (higher risk)
• Patient preference (avoid potential second surgery)

Advantages:

• Definitive; no second surgery needed
• Enables RAI ablation/therapy
• Enables thyroglobulin monitoring for recurrence
• Lower local recurrence rates

Disadvantages:

• Higher complication risk (RLN injury 1-2%, hypoparathyroidism 1-2% permanent)
• Requires lifelong levothyroxine replacement
• More extensive surgery

3. Completion Thyroidectomy

• Removal of remaining thyroid lobe after initial hemithyroidectomy
• Indicated when cancer diagnosed on hemithyroidectomy pathology requiring total thyroidectomy (based on tumor size, extrathyroidal extension, multifocality, lymph node metastases)
• Timing: Typically 2-6 months after initial surgery
• Risk: Higher complication rate than primary total thyroidectomy (scarring, difficult dissection)

4. Lymph Node Dissection

Central Neck Dissection (Level VI):

• Therapeutic: Clinically evident central compartment lymph nodes (N1a)
• Prophylactic: Controversial; may consider for advanced primary tumors (T3/T4)

Lateral Neck Dissection (Levels II-V):

• Therapeutic: Clinically evident or biopsy-proven lateral neck metastases (N1b)
• Comprehensive compartment-oriented dissection (not "berry picking")

Surgical Complications

Exam Detail: 1. Recurrent Laryngeal Nerve (RLN) Injury

Incidence:

• Temporary: 3-5% (resolves within 6 months)
• Permanent: 0.5-2% (experienced surgeons)
• Higher risk: Revision surgery, large goitres, cancer with extrathyroidal extension

Anatomy:

• Right RLN: Loops under subclavian artery; more oblique course
• Left RLN: Loops under aortic arch; more vertical course in neck
• Both enter larynx posterior to cricothyroid joint
• Innervate all intrinsic laryngeal muscles except cricothyroid (external branch of SLN)

Clinical Presentation:

Management:

• Unilateral: Voice therapy; consider medialization thyroplasty if no recovery by 6-12 months
• Bilateral: May require tracheostomy; definitive treatment = arytenoidectomy or lateralization procedure [35]

2. Hypoparathyroidism

Incidence:

• Temporary (transient): 10-30% (resolves within 6 months)
• Permanent: 1-2% after total thyroidectomy; less than 1% after hemithyroidectomy
• Higher risk: Total thyroidectomy, central neck dissection, revision surgery

Mechanism:

• Devascularization (most common; parathyroids' blood supply from inferior thyroid artery)
• Inadvertent removal
• Trauma during dissection

Clinical Presentation:

• Typically manifests 24-72 hours post-op (as calcium drops)
• Symptoms: Perioral paresthesias, fingertip tingling, Chvostek's sign, Trousseau's sign, carpopedal spasm, laryngospasm (severe)
• Labs: ↓ serum calcium, ↓ PTH, ↑ phosphate

Management:

• Mild (Ca > 2.0 mmol/L): Oral calcium carbonate 1-3g/day + calcitriol 0.25-0.5mcg twice daily
• Severe (Ca less than 1.9 mmol/L or symptomatic): IV calcium gluconate 10% 10-20ml over 10min, then infusion
• Monitoring: Check calcium, phosphate, magnesium daily until stable
• Long-term: If persistent > 6 months, diagnose permanent hypoparathyroidism; continue calcium + calcitriol indefinitely [36]

3. Post-operative Bleeding

Incidence: less than 1% but potentially life-threatening

Presentation:

• Typically within first 6-24 hours
• Neck swelling, tense hematoma
• Dyspnea, stridor (tracheal compression)
• EMERGENCY: Airway compromise

Management:

• Immediate: Remove skin sutures at bedside to evacuate hematoma and relieve airway compression
• Prepare for intubation (may be difficult)
• Return to operating room for formal exploration, hemostasis, drain placement

4. External Branch of Superior Laryngeal Nerve (EBSLN) Injury

Incidence: 5-10% (often unrecognized)

Function: Innervates cricothyroid muscle (tenses vocal cords)

Symptoms:

• Voice fatigue
• Reduced vocal range (cannot reach high notes)
• Reduced voice projection
• Asymptomatic in many patients

At-risk population: Singers, teachers, public speakers [35]

5. Thyroid Storm (Rare)

• Acute thyrotoxicosis precipitated by surgery in inadequately prepared hyperthyroid patient
• Prevention: Ensure euthyroid pre-operatively (beta-blockers, ATDs)

6. Hypothyroidism (Expected after total thyroidectomy)

• Requires lifelong levothyroxine replacement
• Target TSH 0.5-2.0 mU/L (low-normal) for thyroid cancer; 0.5-5.0 mU/L for benign disease

Radioactive Iodine (RAI-131) Therapy

Indications:

1. Hyperthyroidism:

• Toxic adenoma (hot nodule)
• Toxic multinodular goitre
• Alternative to surgery; preferred in elderly or high surgical risk

2. Thyroid Cancer:

• Post-thyroidectomy remnant ablation
• Treatment of iodine-avid metastases
• Indications based on ATA risk stratification

Mechanism:

• Iodine-131 emits beta particles (tissue penetration ~2mm)
• Selectively taken up by thyroid follicular cells
• Destroys thyroid tissue (cancer cells or normal thyroid)

Dosing:

• Hyperthyroidism: 10-20 mCi (outpatient)
• Thyroid cancer ablation: 30-150 mCi (may require hospitalization if > 30 mCi due to radiation safety)

Preparation (for thyroid cancer):

• TSH stimulation required (TSH > 30 mU/L)
  • "Method 1: Levothyroxine withdrawal (4-6 weeks; causes symptomatic hypothyroidism)"
  • "Method 2: Recombinant human TSH (rhTSH) injections (avoids hypothyroid symptoms)"
• Low-iodine diet (1-2 weeks before)
• Confirm pregnancy test negative in women of childbearing age

Contraindications:

• Pregnancy (absolute)
• Breastfeeding (absolute)
• Inability to follow radiation safety precautions
• Large goitres with airway compression (RAI can cause thyroiditis and swelling)

Side Effects:

• Radiation thyroiditis (neck pain, swelling; 1-2 weeks post-treatment)
• Sialadenitis (salivary gland inflammation; 10-30%)
• Nausea
• Bone marrow suppression (high cumulative doses)
• Secondary malignancy risk (very small; dose-dependent)
• Permanent hypothyroidism (expected in cancer treatment; common in toxic nodules) [37]

Post-RAI Surveillance (for cancer):

• Thyroglobulin levels (tumor marker)
• Whole-body RAI scan (6-12 months post-ablation)
• Neck ultrasound

Special Populations

Pregnancy:

• Surgery deferred if possible; if necessary, safest in 2nd trimester
• Radioiodine absolutely contraindicated
• FNA safe during pregnancy
• Thyroid cancer does NOT behave more aggressively in pregnancy; can usually defer surgery until post-partum [38]

Children and Adolescents:

• Higher malignancy risk (22-26% of nodules)
• More aggressive surgical approach
• Otherwise, similar evaluation and management principles [17]

Elderly:

• Higher surgical risk; consider comorbidities
• RAI often preferred for toxic nodules
• Smaller, low-risk cancers may be observed

---

9. Complications

Complications of Thyroid Nodules (Untreated)

Complications of FNA

• Pain (mild)
• Bleeding (minimal; hematoma rare less than 1%)
• Infection (exceedingly rare)
• Non-diagnostic sample (10-20%; requires repeat)

Surgical Complications

See detailed discussion under Surgical Management.

Complications of RAI Therapy

See detailed discussion under Radioactive Iodine Therapy.

---

10. Prognosis and Outcomes

Benign Thyroid Nodules

• Natural history: Most remain stable; ~15-20% grow over time
• Malignant transformation: Rare; estimated less than 1% over lifetime
• Functional: Toxic adenomas do not regress; require definitive treatment

Thyroid Cancer Prognosis

Papillary Thyroid Carcinoma:

• Overall: Excellent; > 95% 10-year survival, > 90% 20-year survival [27]
• Stage I: > 99% 10-year survival
• Stage II: ~98% 10-year survival
• Stage III: ~93% 10-year survival
• Stage IV: ~50-70% 10-year survival
• Recurrence: 10-20% over 10 years; majority are locoregional (lymph nodes)
• Mortality: ~1-2% disease-specific mortality

Favorable Prognostic Factors:

• Age less than 55 years
• Female sex
• Small tumor size (less than 2cm)
• Intrathyroidal disease (no extrathyroidal extension)
• No lymph node metastases
• No distant metastases
• Complete surgical resection
• Classic papillary histology (vs aggressive variants)

Unfavorable Prognostic Factors:

• Age ≥55 years
• Male sex
• Tumor size > 4cm
• Extrathyroidal extension
• Lymph node metastases (especially > 5 nodes or nodes > 3cm)
• Distant metastases (lung, bone)
• Incomplete resection
• Aggressive histologic variants (tall cell, columnar cell, hobnail, diffuse sclerosing)
• BRAF V600E mutation (associated with worse outcomes) [27]

Follicular Thyroid Carcinoma:

• Overall: Good; 85-95% 10-year survival [28]
• Minimally invasive (capsular invasion only): > 95% 10-year survival
• Widely invasive (vascular invasion): 60-80% 10-year survival
• With distant metastases: 40-60% 10-year survival
• Recurrence: 10-30%; often distant (lung, bone)

Medullary Thyroid Carcinoma:

• Overall: 70-85% 10-year survival [29]
• Stage I: > 95% 10-year survival
• Stage II: ~90% 10-year survival
• Stage III: 70-80% 10-year survival
• Stage IV: 20-40% 10-year survival
• Hereditary vs sporadic: Similar outcomes if stage-matched
• Calcitonin levels: Post-op undetectable calcitonin predicts excellent outcome; persistent elevation indicates residual disease

Anaplastic Thyroid Carcinoma:

• Overall: Dismal; median survival 3-5 months; less than 5% 1-year survival [30]
• Intrathyroidal (Stage IVA): Slightly better; median ~6-12 months
• Extrathyroidal (Stage IVB): Median 2-6 months
• Distant metastases (Stage IVC): Median 1-3 months
• Treatment: Multimodal (surgery, radiotherapy, chemotherapy); often palliative
• Novel therapies: BRAF inhibitors + MEK inhibitors show promise in BRAF-mutant ATC

Long-term Follow-up

Benign Nodules:

• Ultrasound surveillance initially, may discontinue after 3-5 years if stable
• Annual TSH for patients on thyroid hormone

Thyroid Cancer (post-treatment):

• Low-risk: Less intensive surveillance; ultrasound, thyroglobulin monitoring
• High-risk: Intensive surveillance; ultrasound, thyroglobulin, periodic whole-body RAI scans or PET-CT
• Recurrence: Often treatable; surgery, RAI, or systemic therapy
• Surveillance strategy: Risk-stratified, dynamic (modified based on response to therapy) [7]

---

11. Prevention and Screening

Primary Prevention

Iodine Sufficiency:

• Adequate dietary iodine (150 mcg/day for adults) prevents goitre
• Universal salt iodization programs effective in preventing endemic goitre
• Over-supplementation may increase autoimmune thyroid disease [19]

Radiation Avoidance:

• Minimize unnecessary head/neck radiation, especially in children
• Shield thyroid during diagnostic imaging when feasible
• Survivors of childhood radiation (e.g., for lymphoma, head/neck cancer): Lifelong thyroid surveillance

Genetic Counseling:

• MEN2 families: RET proto-oncogene testing
• Prophylactic thyroidectomy in RET mutation carriers (timing based on specific mutation) [29]

Screening

General Population:

• NOT recommended: No benefit demonstrated for routine thyroid cancer screening
• High false-positive rate (many benign nodules)
• Risk of overdiagnosis and overtreatment (indolent microcarcinomas) [5,6]

High-Risk Populations:

• History of head/neck irradiation: Annual neck palpation; consider ultrasound screening
• Family history of hereditary thyroid cancer syndromes:
  • "MEN2: Genetic testing; prophylactic thyroidectomy if RET-positive"
  • "Familial papillary thyroid cancer: Periodic thyroid ultrasound"
• Large radiation exposure (nuclear accidents): Periodic screening in exposed populations

---

12. Evidence and Guidelines

Key Guidelines

Landmark Studies

1. Increased Detection Without Mortality Benefit

• Davies L, Welch HG. Current thyroid cancer trends in the United States. JAMA Otolaryngol Head Neck Surg. 2014.
• Findings: 3-fold increase in thyroid cancer incidence (1975-2009), almost entirely small papillary cancers; mortality stable
• Implication: Epidemic of overdiagnosis; many detected cancers may never have caused harm [5]

2. Active Surveillance for Papillary Microcarcinoma

• Ito Y, et al. Patient age is significantly related to the progression of papillary microcarcinoma of the thyroid under observation. Thyroid. 2014.
• Findings: Among 1,235 patients with papillary microcarcinoma (less than 1cm) managed with active surveillance, only 8% showed enlargement (> 3mm) at 10 years; no patient developed distant metastases
• Implication: Active surveillance is safe alternative to immediate surgery for low-risk microcarcinomas in selected patients [34]

3. Molecular Testing in Indeterminate Nodules

• Nikiforov YE, et al. Impact of mutational testing on the diagnosis and management of patients with cytologically indeterminate thyroid nodules. J Clin Endocrinol Metab. 2014.
• Findings: Molecular testing (ThyroSeq) in Bethesda III/IV nodules improved diagnostic accuracy and reduced unnecessary surgeries
• Implication: Molecular testing can refine risk and guide management in cytologically indeterminate nodules [33]

4. BRAF Mutation and Prognosis

• Xing M, et al. BRAF mutation predicts a poorer clinical prognosis for papillary thyroid cancer. J Clin Endocrinol Metab. 2005.
• Findings: BRAF V600E mutation associated with extrathyroidal extension, lymph node metastases, advanced stage, and recurrence
• Implication: BRAF mutation is an independent predictor of poor prognosis; may guide extent of surgery and adjuvant therapy [14]

5. Recombinant TSH vs Thyroid Hormone Withdrawal

• Haugen BR, et al. A comparison of recombinant human thyrotropin and thyroid hormone withdrawal for the detection of thyroid remnant or cancer. J Clin Endocrinol Metab. 1999.
• Findings: Recombinant TSH (Thyrogen) equivalent to thyroid hormone withdrawal for preparing patients for RAI, without causing hypothyroid symptoms
• Implication: rhTSH improves quality of life and is now standard for RAI preparation [41]

---

13. Patient and Layperson Explanation

What is a thyroid nodule?

A thyroid nodule is a lump or growth in the thyroid gland, a butterfly-shaped gland in the front of your neck. Think of it like a mole on your skin—very common, and usually harmless. About 1 in 2 people have thyroid nodules if we look carefully with ultrasound, though most are too small to feel.

Should I be worried about cancer?

It's natural to worry, but only about 1 in 20 thyroid nodules is cancer (95% are benign). Even if it is cancer, thyroid cancer is one of the most treatable and curable cancers, with a cure rate over 95%. We have excellent tests (ultrasound and needle biopsy) to determine if your nodule needs treatment.

How did I get a thyroid nodule?

In most cases, we don't know why nodules form. They become more common as we age. Risk factors include:

• Low iodine in diet (less common in countries with iodized salt)
• Family history of thyroid problems
• Previous radiation exposure to the neck (rare)

What tests will I need?

1. Blood test (TSH): Checks if your thyroid is working normally. Takes 1 day for results.

2. Ultrasound: Like the scan used in pregnancy; uses sound waves to create pictures of your thyroid. Painless. Takes 15-30 minutes. Helps determine if the nodule looks benign or if we need a biopsy.

3. Needle biopsy (FNA): If needed based on ultrasound. A very thin needle (like a blood test needle) is inserted into the nodule to collect cells. Takes 5-10 minutes. Mild discomfort. Results in 3-7 days. This is the best test to check for cancer.

What is the treatment?

It depends on what we find:

If benign (not cancer):

• Most common approach: Watch and wait. Repeat ultrasound every 6-12 months to make sure it's not growing.
• If causing symptoms (trouble swallowing, visible lump): Surgery to remove it.

If indeterminate (can't tell from biopsy alone):

• May need surgery to remove half or all of the thyroid to examine it completely under the microscope.

If cancer:

• Surgery to remove thyroid (all or part)
• May need radioactive iodine treatment after surgery (takes place in hospital; very effective)
• Excellent cure rates

Will I need to take medication?

• If we remove half the thyroid: Usually no. The remaining half does the job.
• If we remove the whole thyroid: Yes, you'll take a thyroid hormone pill (levothyroxine) once daily for life. It replaces what your thyroid normally makes. Simple blood test once a year to check the dose.

What are the risks of surgery?

Surgery is generally very safe in experienced hands. Risks include:

• Voice changes (1-2%): From nerve near thyroid. Usually temporary; rarely permanent.
• Low calcium (1-2%): From affecting nearby parathyroid glands. Treated with calcium pills.
• Bleeding, infection (less than 1%): As with any surgery.

What if I do nothing?

• If benign: Usually safe to watch. May grow slowly over years; rarely causes problems.
• If cancer: Delays treatment; cancer may grow or spread. But thyroid cancer usually grows slowly, so a few weeks to make decisions is fine.

Key Takeaways

• Thyroid nodules are very common and usually benign
• Simple tests (ultrasound, biopsy) can determine if treatment is needed
• If cancer is found, it is usually very curable
• Treatment (if needed) is usually surgery, which is safe and effective

---

14. Examination Focus

Common Exam Questions (MRCP, FRCS, MRCOG)

1. Investigation Pathway

Q: "A 45-year-old woman presents with a 2cm thyroid nodule. TSH is normal. What is the next most appropriate investigation?"

A: Thyroid ultrasound.

• Rationale: Normal TSH indicates euthyroid state; nodule is non-functioning. Ultrasound is the gold standard for characterizing thyroid nodules and determining need for FNA based on suspicious features.

2. Cytology Interpretation

Q: "FNA result shows Bethesda IV (Thy3f): Follicular Neoplasm. What is the next step?"

A: Diagnostic hemithyroidectomy (thyroid lobectomy).

• Rationale: FNA cannot distinguish follicular adenoma (benign) from follicular carcinoma (malignant) because the defining feature is capsular/vascular invasion, which requires histologic examination of the entire nodule. Therefore, surgical excision is mandatory for diagnosis. [12,13]

3. Toxic Nodule Management

Q: "A 60-year-old has a solitary thyroid nodule with suppressed TSH (0.05 mU/L). What investigation is most appropriate?"

A: Radionuclide thyroid scan (Tc-99m or I-123).

• Rationale: Suppressed TSH suggests autonomous hyperfunctioning nodule. Isotope scan will confirm "hot" nodule. Hot nodules are almost never malignant (less than 1%), so FNA is not indicated. Treatment options are RAI or surgery for hyperthyroidism. [9]

4. Red Flags

Q: "Which features of a thyroid nodule are most concerning for malignancy?"

A:

• Hard, fixed consistency
• Hoarseness (recurrent laryngeal nerve invasion)
• Rapid growth
• Cervical lymphadenopathy
• History of head/neck irradiation in childhood
• Family history of MEN2 (medullary cancer)
• Male sex, age less than 20 or > 60 years [8,22]

5. Surgical Complications

Q: "A patient develops perioral tingling and positive Chvostek's sign 48 hours after total thyroidectomy. What is the most likely diagnosis and initial management?"

A:

• Diagnosis: Hypocalcemia secondary to hypoparathyroidism (from parathyroid gland devascularization/removal during surgery)
• Initial management:
  • Check serum calcium, PTH, phosphate, magnesium
  • "If symptomatic or Ca less than 1.9 mmol/L: IV calcium gluconate 10ml 10% over 10 minutes"
  • Oral calcium carbonate + calcitriol
  • Monitor calcium daily until stable [36]

6. Papillary Thyroid Cancer Spread

Q: "What is the most common route of spread for papillary thyroid carcinoma?"

A: Lymphatic spread to cervical lymph nodes.

• Rationale: 50-70% of PTC patients have lymph node metastases (often microscopic). Hematogenous spread is rare in PTC (unlike follicular cancer which spreads to lung/bone). [27]

Viva Points

Viva Point: Opening Statement for Thyroid Nodule:

"A thyroid nodule is a discrete lesion within the thyroid gland that is distinct from the surrounding parenchyma. Thyroid nodules are extremely common, detected in up to 50% of adults on ultrasound, but only 5-15% are malignant. The key clinical challenge is identifying the minority that harbor cancer without subjecting all patients to unnecessary surgery."

Structured Approach to Thyroid Nodule:

"I would approach this systematically:

1. History:

• Duration, growth rate (rapid growth concerning)
• Compressive symptoms (dysphagia, dyspnea, hoarseness)
• Hyperthyroid symptoms (if toxic nodule)
• Risk factors for malignancy: Age less than 20 or > 60, male sex, radiation exposure, family history (MEN2, FAP)

2. Examination:

• Palpate thyroid: size, consistency (hard = suspicious), mobility (fixed = suspicious)
• Observe swallowing (thyroid moves up)
• Cervical lymphadenopathy
• Pemberton's sign (if large goitre)
• Signs of thyroid dysfunction

3. Investigations:

• First test: TSH (determines functional status)
  • "If low: Radionuclide scan (hot nodule = low cancer risk; treat hyperthyroidism)"
  • "If normal/high: Thyroid ultrasound (U-score classification)"
• Ultrasound: Characterize nodule; assign risk score (U2-U5)
• FNA: If U3-U5 and size ≥1cm (earlier if high clinical suspicion)
  • Bethesda/Thy classification guides management

4. Management:

• Benign (Thy2): Observation with serial ultrasounds
• Indeterminate (Thy3): Consider molecular testing or hemithyroidectomy
• Follicular neoplasm (Thy3f): Diagnostic hemithyroidectomy (cannot distinguish adenoma from carcinoma on cytology)
• Malignant (Thy5): Total thyroidectomy + possible RAI ablation

5. Complications to Counsel:

• RLN injury (1-2%): Voice change
• Hypoparathyroidism (1-2% permanent): Hypocalcemia requiring calcium/calcitriol
• Hypothyroidism (if total thyroidectomy): Lifelong levothyroxine

6. Prognosis:

• Papillary/follicular cancer: Excellent (> 95% 10-year survival)
• Medullary cancer: Good (70-85% 10-year survival); check for MEN2
• Anaplastic cancer: Dismal (median survival 3-5 months)"

High-Yield Facts

Molecular Markers:

• BRAF V600E: Most common mutation in papillary thyroid cancer (40-45%); associated with aggressive behavior
• RET/PTC: Rearrangements in PTC; associated with radiation exposure
• RAS: Found in follicular neoplasms; activates MAPK and PI3K pathways
• PAX8/PPARγ: Follicular thyroid cancer (30-35%)
• RET proto-oncogene: Germline mutations cause MEN2; somatic mutations in sporadic medullary cancer [14,25,29]

Histologic Hallmarks:

• Papillary Ca: "Orphan Annie eye" nuclei (ground-glass), psammoma bodies (calcifications), papillary architecture
• Follicular Ca: Capsular or vascular invasion (defines malignancy)
• Medullary Ca: C-cell origin, amyloid deposition, calcitonin production
• Anaplastic Ca: Undifferentiated pleomorphic cells, very aggressive

Thyroid Cancer Staging (Age Cutoff):

• AJCC 8th Edition (2017): Changed age cutoff from 45 to 55 years for papillary/follicular cancer staging
• Patients less than 55: Stage I (any T/N, M0) or Stage II (any T/N, M1)
• Patients ≥55: Traditional staging (I-IVB based on T/N/M) [27]

MEN2 Syndromes:

• MEN2A: Medullary thyroid cancer (95%), pheochromocytoma (50%), hyperparathyroidism (20-30%)
• MEN2B: Medullary thyroid cancer (100%, earliest and most aggressive), pheochromocytoma (50%), marfanoid habitus, mucosal neuromas
• Management: Prophylactic thyroidectomy based on RET codon mutation; screen for pheochromocytoma before surgery (anesthetic risk) [29]

Common Mistakes

❌ Mistake 1: Ordering FNA on all thyroid nodules

• Correct approach: Measure TSH first. If suppressed, do radionuclide scan (hot nodules don't need FNA). Only proceed to FNA if euthyroid/hypothyroid AND suspicious ultrasound features.

❌ Mistake 2: Repeating FNA on Thy3f (follicular neoplasm)

• Correct approach: Repeat FNA will NOT provide additional information. FNA cannot distinguish follicular adenoma from carcinoma. Proceed directly to diagnostic hemithyroidectomy.

❌ Mistake 3: Assuming all papillary microcarcinomas (less than 1cm) need immediate surgery

• Correct approach: Active surveillance is a safe alternative for low-risk microcarcinomas in selected patients, particularly younger patients without suspicious features. [34]

❌ Mistake 4: Forgetting to check for pheochromocytoma before thyroid surgery in MEN2 patient

• Correct approach: ALWAYS screen for pheochromocytoma (plasma metanephrines) in MEN2 patients before any surgery. Undiagnosed pheochromocytoma can cause fatal hypertensive crisis during anesthesia. [29]

❌ Mistake 5: Using serum thyroglobulin to diagnose primary thyroid cancer

• Correct approach: Thyroglobulin is NOT useful for diagnosing primary thyroid cancer (many benign nodules produce thyroglobulin). It is used ONLY for post-thyroidectomy surveillance to detect recurrence.

Model Answer: "Describe your approach to a patient with a thyroid nodule"

"I would approach this systematically, beginning with a thorough history and examination, followed by risk-stratified investigation and management.

History: I would ask about the duration and rate of growth of the nodule, any compressive symptoms such as dysphagia, dyspnea, or hoarseness (which would suggest recurrent laryngeal nerve involvement and raise suspicion for malignancy), and symptoms of thyroid dysfunction. Importantly, I would assess for risk factors for thyroid cancer including age less than 20 or greater than 60 years, male sex, history of head and neck irradiation in childhood, and family history of thyroid cancer or MEN2 syndrome.

Examination: I would inspect the neck for visible swelling and observe swallowing. On palpation, I would assess the nodule's size, consistency (hard and fixed would be concerning), and mobility with swallowing. I would examine for cervical lymphadenopathy. If a large goitre was present, I would perform Pemberton's sign to assess for retrosternal extension and thoracic inlet obstruction.

Investigations: The first and most important test is serum TSH. If TSH is low, suggesting autonomous function, I would arrange a radionuclide thyroid scan as hyperfunctioning 'hot' nodules carry very low malignancy risk and the priority is treating hyperthyroidism. If TSH is normal or high, I would proceed to high-resolution thyroid ultrasound to characterize the nodule using a risk stratification system such as the BTA U-score or ACR TI-RADS. Fine needle aspiration would be indicated for nodules ≥1cm with indeterminate or suspicious ultrasound features (U3-U5), with cytology classified using the Bethesda system.

Management: For benign cytology (Bethesda II/Thy2), I would recommend observation with serial ultrasounds. For follicular neoplasm (Bethesda IV/Thy3f), I would recommend diagnostic hemithyroidectomy as FNA cannot distinguish adenoma from carcinoma—this requires histologic examination of the capsule for invasion. For suspicious or malignant cytology (Bethesda V-VI), I would discuss the case in a multidisciplinary meeting and typically recommend total thyroidectomy for most thyroid cancers, with consideration of radioactive iodine ablation post-operatively based on risk stratification.

I would counsel the patient on surgical risks including recurrent laryngeal nerve injury (1-2% permanent), hypoparathyroidism (1-2% permanent), and the need for lifelong levothyroxine replacement if total thyroidectomy is performed. For thyroid cancer, I would emphasize the excellent prognosis, with over 95% 10-year survival for papillary and follicular cancers.

This approach aligns with current British Thyroid Association and American Thyroid Association guidelines."

---

15. References

1. Dean DS, Gharib H. Epidemiology of thyroid nodules. Best Pract Res Clin Endocrinol Metab. 2008;22(6):901-911. doi:10.1016/j.beem.2008.09.019

2. Guth S, Theune U, Aberle J, Galach A, Bamberger CM. Very high prevalence of thyroid nodules detected by high frequency (13 MHz) ultrasound examination. Eur J Clin Invest. 2009;39(8):699-706. doi:10.1111/j.1365-2362.2009.02162.x

3. Hegedüs L. Clinical practice. The thyroid nodule. N Engl J Med. 2004;351(17):1764-1771. doi:10.1056/NEJMcp031436

4. Yoon DY, Chang SK, Choi CS, et al. The prevalence and significance of incidental thyroid nodules identified on computed tomography. J Comput Assist Tomogr. 2008;32(5):810-815. doi:10.1097/RCT.0b013e318157fd38

5. Davies L, Welch HG. Current thyroid cancer trends in the United States. JAMA Otolaryngol Head Neck Surg. 2014;140(4):317-322. doi:10.1001/jamaoto.2014.1

6. Perros P, Boelaert K, Colley S, et al. Guidelines for the management of thyroid cancer. Clin Endocrinol (Oxf). 2014;81 Suppl 1:1-122. doi:10.1111/cen.12515

7. Haugen BR, Alexander EK, Bible KC, et al. 2015 American Thyroid Association Management Guidelines for Adult Patients with Thyroid Nodules and Differentiated Thyroid Cancer. Thyroid. 2016;26(1):1-133. doi:10.1089/thy.2015.0020

8. Bomeli SR, LeBeau SO, Ferris RL. Evaluation of a thyroid nodule. Otolaryngol Clin North Am. 2010;43(2):229-238. doi:10.1016/j.otc.2010.01.002

9. Gharib H, Papini E, Garber JR, et al. American Association of Clinical Endocrinologists, American College of Endocrinology, and Associazione Medici Endocrinologi Medical Guidelines for Clinical Practice for the Diagnosis and Management of Thyroid Nodules--2016 Update. Endocr Pract. 2016;22(5):622-639. doi:10.4158/EP161208.GL

10. Abboud B, Sleilaty G, Mansour E, et al. Is there a relationship between goiter and cancer in an endemic goiter area? ANZ J Surg. 2005;75(9):730-732. doi:10.1111/j.1445-2197.2005.03517.x

11. Pemberton HS. Sign of submerged goitre. Lancet. 1946;2:509.

12. Cibas ES, Ali SZ. The 2017 Bethesda System for Reporting Thyroid Cytopathology. Thyroid. 2017;27(11):1341-1346. doi:10.1089/thy.2017.0500

13. Bongiovanni M, Spitale A, Faquin WC, Mazzucchelli L, Baloch ZW. The Bethesda System for Reporting Thyroid Cytopathology: a meta-analysis. Acta Cytol. 2012;56(4):333-339. doi:10.1159/000339959

14. Xing M. BRAF mutation in thyroid cancer. Endocr Relat Cancer. 2005;12(2):245-262. doi:10.1677/erc.1.0978

15. Mortensen JD, Woolner LB, Bennett WA. Gross and microscopic findings in clinically normal thyroid glands. J Clin Endocrinol Metab. 1955;15(10):1270-1280. doi:10.1210/jcem-15-10-1270

16. Lim H, Devesa SS, Sosa JA, Check D, Kitahara CM. Trends in Thyroid Cancer Incidence and Mortality in the United States, 1974-2013. JAMA. 2017;317(13):1338-1348. doi:10.1001/jama.2017.2719

17. Francis GL, Waguespack SG, Bauer AJ, et al. Management Guidelines for Children with Thyroid Nodules and Differentiated Thyroid Cancer. Thyroid. 2015;25(7):716-759. doi:10.1089/thy.2014.0460

18. Ezzat S, Sarti DA, Cain DR, Braunstein GD. Thyroid incidentalomas. Prevalence by palpation and ultrasonography. Arch Intern Med. 1994;154(16):1838-1840.

19. Zimmermann MB, Galetti V. Iodine intake as a risk factor for thyroid cancer: a comprehensive review of animal and human studies. Thyroid Res. 2015;8:8. doi:10.1186/s13044-015-0020-8

20. Schneider AB, Sarne DH. Long-term risks for thyroid cancer and other neoplasms after exposure to radiation. Nat Clin Pract Endocrinol Metab. 2005;1(2):82-91. doi:10.1038/ncpendmet0020

21. Ngeow J, Sesock K, Eng C. Clinical implications of germline PTEN mutations in Cowden syndrome and related disorders. Expert Rev Endocrinol Metab. 2017;12(6):397-406. doi:10.1080/17446651.2017.1397506

22. Welker MJ, Orlov D. Thyroid nodules. Am Fam Physician. 2003;67(3):559-566.

23. Nussey S, Whitehead S. The thyroid gland. In: Endocrinology: An Integrated Approach. Oxford: BIOS Scientific Publishers; 2001. Chapter 3.

24. Krohn K, Führer D, Bayer Y, et al. Molecular pathogenesis of euthyroid and toxic multinodular goiter. Endocr Rev. 2005;26(4):504-524. doi:10.1210/er.2004-0005

25. Nikiforov YE, Nikiforova MN. Molecular genetics and diagnosis of thyroid cancer. Nat Rev Endocrinol. 2011;7(10):569-580. doi:10.1038/nrendo.2011.142

26. Frates MC, Benson CB, Doubilet PM, et al. Prevalence and distribution of carcinoma in patients with solitary and multiple thyroid nodules on sonography. J Clin Endocrinol Metab. 2006;91(9):3411-3417. doi:10.1210/jc.2006-0690

27. Schlumberger M, Tahara M, Wirth LJ, et al. Lenvatinib versus placebo in radioiodine-refractory thyroid cancer. N Engl J Med. 2015;372(7):621-630. doi:10.1056/NEJMoa1406470

28. Chow SM, Law SC, Chan JK, Au SK, Yau S, Lau WH. Papillary microcarcinoma of the thyroid-Prognostic significance of lymph node metastasis and multifocality. Cancer. 2003;98(1):31-40. doi:10.1002/cncr.11442

29. Wells SA Jr, Asa SL, Dralle H, et al. Revised American Thyroid Association guidelines for the management of medullary thyroid carcinoma. Thyroid. 2015;25(6):567-610. doi:10.1089/thy.2014.0335

30. Smallridge RC, Ain KB, Asa SL, et al. American Thyroid Association guidelines for management of patients with anaplastic thyroid cancer. Thyroid. 2012;22(11):1104-1139. doi:10.1089/thy.2012.0302

31. Graff-Baker A, Roman SA, Thomas DC, Udelsman R, Sosa JA. Prognosis of primary thyroid lymphoma: demographic, clinical, and pathologic predictors of survival in 1,408 cases. Surgery. 2009;146(6):1105-1115. doi:10.1016/j.surg.2009.09.020

32. Tessler FN, Middleton WD, Grant EG, et al. ACR Thyroid Imaging, Reporting and Data System (TI-RADS): White Paper of the ACR TI-RADS Committee. J Am Coll Radiol. 2017;14(5):587-595. doi:10.1016/j.jacr.2017.01.046

33. Nikiforov YE, Carty SE, Chiosea SI, et al. Highly accurate diagnosis of cancer in thyroid nodules with follicular neoplasm/suspicious for a follicular neoplasm cytology by ThyroSeq v2 next-generation sequencing assay. Cancer. 2014;120(23):3627-3634. doi:10.1002/cncr.29038

34. Ito Y, Miyauchi A, Kihara M, Higashiyama T, Kobayashi K, Miya A. Patient age is significantly related to the progression of papillary microcarcinoma of the thyroid under observation. Thyroid. 2014;24(1):27-34. doi:10.1089/thy.2013.0367

35. Jeannon JP, Orabi AA, Bruch GA, Abdalsalam HA, Simo R. Diagnosis of recurrent laryngeal nerve palsy after thyroidectomy: a systematic review. Int J Clin Pract. 2009;63(4):624-629. doi:10.1111/j.1742-1241.2008.01875.x

36. Edafe O, Antakia R, Laskar N, Uttley L, Balasubramanian SP. Systematic review and meta-analysis of predictors of post-thyroidectomy hypocalcaemia. Br J Surg. 2014;101(4):307-320. doi:10.1002/bjs.9384

37. Sawka AM, Brierley JD, Tsang RW, et al. An updated systematic review and commentary examining the effectiveness of radioactive iodine remnant ablation in well-differentiated thyroid cancer. Endocrinol Metab Clin North Am. 2008;37(2):457-480. doi:10.1016/j.ecl.2008.02.007

38. Stagnaro-Green A, Abalovich M, Alexander E, et al. Guidelines of the American Thyroid Association for the diagnosis and management of thyroid disease during pregnancy and postpartum. Thyroid. 2011;21(10):1081-1125. doi:10.1089/thy.2011.0087

39. Pacini F, Schlumberger M, Dralle H, et al. European consensus for the management of patients with differentiated thyroid carcinoma of the follicular epithelium. Eur J Endocrinol. 2006;154(6):787-803. doi:10.1530/eje.1.02158

40. National Comprehensive Cancer Network. Thyroid Carcinoma (Version 2.2023). https://www.nccn.org/professionals/physician_gls/pdf/thyroid.pdf

41. Haugen BR, Pacini F, Reiners C, et al. A comparison of recombinant human thyrotropin and thyroid hormone withdrawal for the detection of thyroid remnant or cancer. J Clin Endocrinol Metab. 1999;84(11):3877-3885. doi:10.1210/jcem.84.11.6094

---

Medical Disclaimer: MedVellum content is for educational purposes and clinical reference. Clinical decisions should account for individual patient circumstances. Always consult appropriate specialists and current guidelines for patient care.