Papillary thyroid carcinoma is the most common thyroid malignancy. Which histological features are PATHOGNOMONIC of papillary carcinoma, even in the absence of papillae?

• A Psammoma bodies and thick colloid
• B Capsular and vascular invasion with follicular architecture
• C Amyloid stroma with calcitonin-secreting cells
• D Orphan Annie eye nuclei (nuclear clearing) and nuclear grooves ✓

Explanation

The pathognomonic nuclear features of papillary thyroid carcinoma are 'Orphan Annie eye' nuclei (optically clear/ground-glass chromatin) and nuclear grooves, with occasional intranuclear pseudoinclusions. These nuclear changes reflect altered nuclear import/export and rearrangements (BRAF V600E, RET/PTC, RAS mutations) and allow diagnosis even in follicular-patterned variants. Capsular/vascular invasion distinguishes follicular carcinoma from adenoma. Amyloid and calcitonin are features of medullary carcinoma.

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

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