A 68-year-old man presents with a rapidly enlarging, hard, fixed thyroid mass causing stridor and dysphagia over 4 weeks. Core biopsy shows markedly pleomorphic spindle cells, multinucleated giant cells, and numerous mitoses with necrosis. Which diagnosis is most likely?

• A Riedel thyroiditis
• B Anaplastic (undifferentiated) thyroid carcinoma ✓
• C Diffuse large B-cell lymphoma of thyroid
• D Medullary thyroid carcinoma

Explanation

Anaplastic thyroid carcinoma typically presents in the elderly with a rapidly enlarging thyroid mass causing compressive symptoms. Histology shows marked pleomorphism, spindle cells, giant cells, necrosis, and high mitotic activity. Riedel thyroiditis shows dense fibrosis without pleomorphism. Lymphoma shows diffuse lymphoid infiltrate, and MTC shows nested neuroendocrine cells with amyloid, none matching the pleomorphic spindle/giant cell morphology described.

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.