A 42-year-old man with a history of type 2 diabetes mellitus and hypertension presents with a 4-month history of episodic severe headaches, excessive sweating, and chest palpitations. His blood pressure fluctuates between 140/90 mmHg and 190/110 mmHg. He denies fever, weight loss, or focal neurologic symptoms. Routine biochemistry shows fasting glucose 198 mg/dL and serum calcium 9.2 mg/dL (normal). A 24-hour urine metanephrines collection shows elevated levels (1.8 μmol/24 h; normal <0.9 μmol/24 h). Contrast-enhanced CT abdomen reveals a 2.2 cm right adrenal mass with homogeneous enhancement. Which of the following additional investigations is most important to exclude before proceeding to surgery?

Explanation

## Syndromic Pheochromocytoma: Genetic Screening Before Surgery ### Clinical Context This patient has biochemically confirmed pheochromocytoma (elevated 24-hour urine metanephrines) with a unilateral adrenal mass on imaging. Before proceeding to adrenalectomy, it is essential to identify whether this is part of a hereditary syndrome, as syndromic pheochromocytomas are bilateral in 30–50% of cases and are associated with other malignancies. ### High-Yield: Hereditary Pheochromocytoma Syndromes | Syndrome | Gene | Key Features | Bilateral Risk | Associated Tumors | |----------|------|--------------|-----------------|-------------------| | **MEN 2A** | RET | Medullary thyroid carcinoma, pheochromocytoma, primary hyperparathyroidism | 50% | MTC, hyperparathyroidism | | **MEN 2B** | RET | Medullary thyroid carcinoma, pheochromocytoma, mucosal neuromas, marfanoid habitus | 50% | MTC, neuromas, GI ganglioneuromas | | **NF1** | NF1 | Neurofibromatosis type 1, café-au-lait spots, optic nerve gliomas | 20–30% | Optic nerve glioma, sarcoma | | **SDH mutations** (SDHA, SDHB, SDHD, SDHAF2) | SDH genes | Familial paragangliomas, often extra-adrenal | 30–70% | Renal cell carcinoma, GI stromal tumors | ### Why RET Mutation Testing is Most Important **Key Point:** MEN 2A and MEN 2B are the most common syndromic causes of pheochromocytoma in the general population. RET proto-oncogene mutations account for ~5% of apparently sporadic pheochromocytomas. **Clinical Pearl:** If RET mutation is present, the patient requires: 1. **Thyroid screening:** Medullary thyroid carcinoma (MTC) develops in nearly 100% of MEN 2 carriers by age 50 if untreated. Prophylactic thyroidectomy is indicated in childhood if RET mutation is confirmed. 2. **Parathyroid screening:** Primary hyperparathyroidism in MEN 2A. 3. **Bilateral adrenal imaging:** Pheochromocytomas are bilateral in 50% of MEN 2 cases; unilateral surgery alone is insufficient. ### Why Other Investigations Are Less Critical **Thyroid ultrasound and TSH** (Option B): While important in MEN 2 syndrome, TSH and routine thyroid ultrasound do not directly identify the genetic risk. Genetic testing (RET mutation) is the definitive screening tool and guides the need for detailed thyroid assessment. **Plasma renin activity and aldosterone-to-renin ratio** (Option C): This tests for primary hyperaldosteronism, a different cause of hypertension unrelated to pheochromocytoma management. Not relevant to syndromic screening. **Serum prolactin and 24-hour urinary free cortisol** (Option D): These screen for prolactinoma and Cushing syndrome, respectively—neither is associated with pheochromocytoma syndromes. Cortisol excess may coexist in ectopic ACTH syndrome, but is not a syndromic feature of pheochromocytoma. ### Preoperative Syndromic Screening Algorithm ```mermaid flowchart TD A[Pheochromocytoma confirmed<br/>Adrenal mass on imaging]:::outcome --> B{Age at presentation<br/>and family history?}:::decision B -->|Age <40 or family Hx| C[Genetic testing:<br/>RET, NF1, SDH genes]:::action B -->|Age >50, no Hx| D[Consider genetic testing<br/>based on tumor size/location]:::action C -->|RET mutation positive| E[MEN 2 syndrome]:::outcome E --> F[Thyroid ultrasound<br/>+ serum calcitonin]:::action E --> G[Parathyroid assessment<br/>serum calcium/PTH]:::action E --> H[Bilateral adrenal imaging<br/>consider bilateral adrenalectomy]:::action C -->|SDH mutation positive| I[Familial paraganglioma]:::outcome I --> J[Screen for extra-adrenal tumors<br/>renal, GI]:::action C -->|NF1 mutation positive| K[Neurofibromatosis type 1]:::outcome K --> L[Ophthalmologic exam<br/>for optic nerve glioma]:::action ``` **Mnemonic:** **PHEO-SYNDROMES** = Pheochromocytoma + Hereditary syndromes - **P**aragangliomas (SDH) - **H**ypertension (all) - **E**xtra-adrenal tumors (SDH, NF1) - **O**ncogenes (RET, NF1, SDH) - **S**creening (genetic testing before surgery) - **Y**oung age (consider syndromic if <40) - **N**eurofibromatosis (NF1) - **D**ual tumors (bilateral adrenal, MTC in MEN 2) - **R**EN proto-oncogene (MEN 2A/2B) - **O**ther malignancies (MTC, renal, GI) - **M**ultiple endocrine neoplasia (MEN 2) - **E**xtra-adrenal paragangliomas (SDH) - **S**urgery planning (unilateral vs bilateral) [cite:Harrison 21e Ch 405; Robbins 10e Ch 24]