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A 42-year-old woman presents with a 2 cm solitary thyroid nodule. Ultrasound shows a hypoechoic solid nodule with microcalcifications. FNA cytology shows nuclear grooves and pseudoinclusions (Bethesda VI).
Questions
a) What is the diagnosis and which gene mutation is most commonly associated? (2 marks)
Papillary thyroid carcinoma (Bethesda VI = malignant). BRAF V600E mutation in 40-60%. Spreads via lymphatics to cervical nodes.
b) Why is FNA unable to diagnose follicular carcinoma? (2 marks)
Follicular adenoma and follicular carcinoma are cytologically identical on FNA — both show benign follicular cells. Diagnosis of follicular carcinoma requires histological demonstration of capsular or vascular invasion on the surgical specimen. Bethesda IV (follicular neoplasm) requires diagnostic lobectomy.
c) A patient with medullary thyroid carcinoma needs surgery. What must be excluded first and why? (3 marks)
Pheochromocytoma must be excluded (plasma metanephrines) before thyroid surgery. Medullary carcinoma is associated with MEN2 — an undiagnosed pheochromocytoma can cause fatal intraoperative hypertensive crisis during thyroidectomy.
d) Describe the surgical management of a 4 cm papillary carcinoma with extrathyroidal extension and nodal metastases. (3 marks)
Total thyroidectomy with central neck dissection (level VI). Followed by radioactive iodine (I-131) ablation and TSH suppression therapy (levothyroxine to TSH below 0.1). Monitor with thyroglobulin and neck ultrasound.