A 35-year-old woman undergoes thyroid biopsy for a solitary nodule. Histology shows follicular cells arranged in follicles without papillary architecture. Nuclear features are absent. Vascular and/or capsular invasion is demonstrated. What is the diagnosis and the clinical significance of vascular invasion pattern?
- A Papillary thyroid carcinoma — nuclear clearing and grooves are diagnostic
- B Hurthle cell (oncocytic) carcinoma — requires presence of >75% oncocytic cells
- C Medullary thyroid carcinoma — amyloid stroma and calcitonin immunopositivity are required
- D Follicular thyroid carcinoma — distinguished from follicular adenoma only by capsular or vascular invasion; extensive vascular invasion predicts hematogenous metastases ✓
Explanation
Follicular thyroid carcinoma (FTC) is diagnosed solely by the presence of capsular invasion (transcapsular tumor extension) and/or vascular invasion; it cannot be distinguished from follicular adenoma on cytology or frozen section. Minimally invasive FTC (limited capsular invasion only) has an excellent prognosis, while widely invasive FTC (extensive vascular invasion into multiple vessels) has significantly higher rates of hematogenous metastases (lung, bone) and reduced survival. Papillary carcinoma is diagnosed by nuclear features (Orphan Annie nuclei, nuclear grooves, pseudoinclusions).
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
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Written and medically reviewed by the StethoPrep medical team.