A 30-year-old patient presents with episodic headache, sweating, palpitations, and hypertension. 24-hour urine shows markedly elevated catecholamines and metanephrines. CT scan shows a 4 cm right adrenal mass. Histological examination of the resected specimen cannot reliably distinguish benign from malignant pheochromocytoma based on:

• A Metastasis to non-chromaffin tissue sites (lymph nodes, liver, bone, lung) ✓
• B Presence of capsular or vascular invasion on histology
• C Cellular pleomorphism, nuclear atypia, and increased mitotic activity alone
• D PASS score (pheochromocytoma of the adrenal gland scaled score) >6

Explanation

Malignancy in pheochromocytoma cannot be established by histological features alone, including capsular invasion, vascular invasion, necrosis, or cellular pleomorphism — all of which can be seen in benign tumors. The only absolute criterion for malignancy is the presence of metastases at sites where chromaffin tissue does not normally exist (liver, lung, bone, distant lymph nodes). Approximately 10% of pheochromocytomas are malignant, and this is more common in extra-adrenal paragangliomas and in SDHB mutation carriers. The PASS score provides a risk estimate but is not diagnostic. Genetic testing for SDH mutations is recommended in all pheochromocytoma patients.

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

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Written and medically reviewed by the StethoPrep medical team.