Medullary thyroid carcinoma (MTC) is derived from parafollicular C cells and secretes calcitonin. On histology, the stroma characteristically contains:
- A Psammoma bodies (concentric calcifications)
- B Amyloid deposits (derived from procalcitonin/calcitonin fibrils) staining positive with Congo red and showing apple-green birefringence ✓
- C Hyalinized collagen bands without amyloid
- D Chondroid metaplasia
Correct answer: B. Amyloid deposits (derived from procalcitonin/calcitonin fibrils) staining positive with Congo red and showing apple-green birefringence
Explanation
The stroma of medullary thyroid carcinoma characteristically contains amyloid composed of misfolded calcitonin and procalcitonin fragments. This amyloid stains with Congo red and shows apple-green birefringence under polarized light. Immunohistochemistry for calcitonin is the key diagnostic marker (also CEA, chromogranin A). Psammoma bodies (laminated calcifications) are characteristic of papillary thyroid carcinoma and serous carcinomas. The presence of stromal amyloid in a thyroid tumor is highly suggestive of MTC on FNA or core biopsy.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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