Fine-needle aspiration of a firm 2 cm thyroid nodule in a 44-year-old man shows nests of spindle-shaped cells amid amorphous eosinophilic material that stains with Congo red. Serum calcitonin is markedly elevated. The most likely diagnosis is:

• A Papillary thyroid carcinoma
• B Follicular thyroid carcinoma
• C Anaplastic thyroid carcinoma
• D Medullary thyroid carcinoma ✓

Explanation

Medullary carcinoma arises from parafollicular D cells, secretes calcitonin, and characteristically produces amyloid stroma derived from procalcitonin that stains with Congo red. Papillary carcinoma shows Orphan Annie eye nuclei, psammoma bodies and papillae, which are absent here. Follicular carcinoma lacks amyloid and does not raise calcitonin. Anaplastic carcinoma occurs in elderly patients as a rapidly enlarging mass with pleomorphic giant cells. Germline RET testing and prophylactic thyroidectomy apply to familial cases.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.