Solitary Thyroid Nodule

Differential Diagnosis

• Colloid nodule / multinodular goiter (MNG)
• Follicular adenoma
• Simple cyst
• Focal thyroiditis
• Carcinoma (papillary, follicular, medullary, anaplastic)
• Status post hemithyroidectomy
• Hemiagenesis
• Metastasis to thyroid

• Thyroglossal duct cyst
• Lymph node
• Parathyroid cyst
• Cystic hygroma, dermoid, teratoma
• Laryngocele

History - Red Flags for Malignancy

• Radiation history: Low-dose therapeutic radiation (for tinea capitis, acne, tonsillar hypertrophy) confers ~40% risk of malignancy in any resulting nodule. Risk peaks 20-30 years after exposure. After Chernobyl, children showed a marked surge in papillary thyroid cancer within 4 years.
• Pain is usually hemorrhage into a benign nodule or thyroiditis; aching in the neck can also occur with medullary thyroid carcinoma (MTC).
• Hoarseness suggests possible recurrent laryngeal nerve (RLN) involvement by malignancy.
• Family history: MEN2 syndromes (medullary carcinoma + pheochromocytoma + hyperparathyroidism), Cowden disease (PTEN mutation - follicular thyroid carcinoma), Gardner syndrome (polyposis coli + papillary thyroid carcinoma).

Physical Examination

• Nodules are palpable when ≥1 cm; smaller ones are found incidentally on imaging.
• Firmness of the nodule increases the risk of malignancy 2-3 fold.
• Nodules >2 cm and solid lesions have higher incidence of carcinoma.
• Fixation to surrounding structures is strongly suspicious.
• Cervical lymphadenopathy adjacent to the nodule raises suspicion; it can be the only presenting sign of thyroid carcinoma.
• Check if the nodule moves with swallowing (thyroid origin) vs. non-thyroid.
• Assess for substernal extension: inferior aspect below the clavicle; Pemberton's maneuver (arms raised above head eliciting facial flushing + venous engorgement = thoracic inlet obstruction).

Investigations

1. Serum TSH (First-Line)

• Suppressed TSH (hyperthyroid): Perform radionuclide scan - risk of malignancy is only ~1% in hot nodules.
• Elevated TSH (hypothyroid): Treat appropriately, then perform FNAC.
• Normal TSH (euthyroid): Most patients - proceed directly to ultrasound + FNAC.

2. Ultrasound (US) - Most Important Imaging

• Differentiates solid vs. cystic nodules.
• Identifies sonographic features raising malignancy risk: microcalcifications, hypoechoic solid nodule, irregular margins, taller-than-wide shape, absent halo, abnormal regional nodes.
• Guides FNAC for difficult-to-palpate nodules.
• Preferred for surveillance of benign nodules.
• Elastography: malignant nodules are stiffer (less deformable) than benign; newer technique, still being validated.
• Contrast-enhanced ultrasound (CEUS): A 2026 meta-analysis (Huo et al., PMID 42262145) shows emerging diagnostic utility for nodule characterization.

3. Fine Needle Aspiration Biopsy (FNAB) - Gold Standard

• Difficult-to-palpate nodules
• Cystic/solid-cystic nodules recurring after prior aspiration
• Multinodular goiters

4. Radionuclide Scanning (¹²³I or ⁹⁹ᵐTc)

• NOT routine - use only if TSH is suppressed (to confirm hot/warm nodule) or after indeterminate FNAC.
• Cold nodules: 95% of all nodules; malignancy rate 10-15%.
• Hot nodules: malignancy rate ~4% (benign autonomous nodule usually).
• ⁹⁹ᵐTc: tests iodine transport only, faster (1 day), less radiation; cannot penetrate sternum.
• ¹²³I: tests transport AND organification; 2 days; preferred for substernal extension.

5. CT / MRI

• Not routine for thyroid nodule evaluation.
• Indicated for: substernal lesions, large/fixed tumors, suspected visceral compartment invasion, mediastinal adenopathy.
• Caution: iodinated CT contrast delays postoperative RAI therapy by 2-3 months.
• MRI superior to CT for distinguishing recurrent tumor vs. postoperative fibrosis.

6. Laboratory Tests

• Serum TSH - always
• Serum calcitonin - if MTC or MEN2 suspected (family history, FNAB suspicious for MTC)
• Serum thyroglobulin (Tg) - cannot differentiate benign from malignant preoperatively; used for post-thyroidectomy surveillance
• RET oncogene mutation testing - all patients with confirmed MTC; 24-hr urine VMA/metanephrines to rule out pheochromocytoma

Bethesda Classification of FNAB Results + Management

• Benign (II): Most common result. Includes colloid nodule, follicular adenoma, Hashimoto's, granulomatous thyroiditis. Cysts are aspirated; if they reaccumulate 3 times, thyroidectomy is recommended. Colloid nodules are observed; thyroidectomy if continued growth or compressive symptoms.
• FN/Suspicious for FN (IV): Up to 35% of Bethesda IV lesions are actually hyperplastic follicular proliferations, not true neoplasms. Lobectomy is preferred as it is both diagnostic and potentially therapeutic.
• Malignant (VI): Near-total or total thyroidectomy.

Molecular Marker Testing (for Indeterminate FNAB)

Management Algorithm Summary

1. History + Physical Exam - identify high-risk features
2. Serum TSH
   • Suppressed → Radionuclide scan → hot nodule = treat medically; cold nodule = FNAB
   • Normal/elevated → Ultrasound + FNAB
3. FNAB result guides surgical vs. conservative management (Bethesda criteria)
4. Surgery for: malignant/suspicious cytology, follicular neoplasm, cyst reaccumulating ×3, symptomatic growth, history of radiation exposure, high-risk clinical features

Special Situations

• Radiation-exposed patients: Even a nodule showing benign FNAB cytology may harbor cancer in a separate nodule in 40% of cases - near-total thyroidectomy may be warranted.
• Children (<20 years): 20-50% malignancy rate with STN - aggressive workup mandatory.
• Elderly males: Higher incidence of nodular disease; malignancy if found has worse prognosis.
• MEN2 / Medullary thyroid carcinoma: Confirm RET mutation, rule out pheochromocytoma before surgery.

Recent evidence update: A 2025 systematic review (Lim et al., PMID 40658618) confirms efficacy and safety of thermal ablation (radiofrequency, microwave, laser) as a non-surgical option for indeterminate benign thyroid nodules, offering volume reduction while preserving thyroid function.

1. Definition & epidemiology - present in ~4% of the US population
2. Differential diagnosis - 95% benign (colloid nodule, adenoma, cyst, focal thyroiditis, carcinoma)
3. History & red flags for malignancy (age <30/>60, male sex, radiation exposure, rapid growth, hoarseness, lymphadenopathy, fixation)
4. Physical examination findings
5. Investigations - TSH, ultrasound, FNAB (gold standard), radionuclide scan, CT/MRI, lab tests
6. Bethesda classification (I-VI) with malignancy risk and management per category
7. Molecular marker testing (Afirma, ThyroSeq, ThyGenX) for indeterminate FNAC
8. Management algorithm flowchart
9. Special situations (radiation exposure, children, MEN2)