A 35-year-old woman undergoes thyroidectomy for a 2.5 cm solitary thyroid nodule. Histology shows follicular patterned cells with nuclear features including nuclear clearing, nuclear grooves, and pseudoinclusions. There is capsular and vascular invasion. Which thyroid carcinoma is this?

• A Follicular thyroid carcinoma with nuclear atypia
• B Papillary thyroid carcinoma — follicular variant ✓
• C Hurthle cell (oncocytic) carcinoma
• D Medullary thyroid carcinoma

Explanation

Papillary thyroid carcinoma (PTC) is diagnosed by its nuclear features, regardless of architectural pattern: nuclear clearing ('Orphan Annie eye' nuclei), nuclear grooves, and intranuclear cytoplasmic pseudoinclusions. The follicular variant of PTC has a follicular architectural pattern (resembling follicular carcinoma) but retains the characteristic PTC nuclear features. The diagnosis of PTC is nuclear-feature based, not architectural. Vascular and capsular invasion in the follicular variant carries a prognosis similar to or slightly worse than classic PTC. Follicular carcinoma lacks PTC nuclear features; medullary carcinoma shows amyloid stroma and is calcitonin-positive.

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

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Written and medically reviewed by the StethoPrep medical team.