A 52-year-old woman with a history of hypertension is found to have a 3 cm left adrenal mass on abdominal imaging done for unrelated reasons. She is asymptomatic with normal blood pressure readings over the past 6 months. Routine biochemistry is normal. Which investigation is most appropriate to exclude a clinically silent pheochromocytoma?

Explanation

## Biochemical Screening for Incidental Adrenal Mass ### Clinical Scenario: Incidentaloma The patient has an **incidentally discovered adrenal mass** (3 cm) that is: - Asymptomatic (no hypertensive episodes, sweating, palpitations) - Associated with normal blood pressure - Found on imaging for unrelated indication **Key Point:** All adrenal incidentalomas ≥1 cm require biochemical screening to exclude pheochromocytoma, even if asymptomatic, because 5–15% of incidentalomas are pheochromocytomas. ### Investigation Strategy for Incidentaloma | Investigation | Indication | Sensitivity | |---|---|---| | **24-hour urine metanephrines + catecholamines** | **First-line screening for all incidentalomas** | **96–99%** | | Plasma free metanephrines (supine) | Alternative if urine unavailable; less sensitive | 89% | | Plasma catecholamines | Poor sensitivity, not recommended | 60–70% | | Adrenal vein sampling | Diagnostic/therapeutic, not screening | N/A | | Dexamethasone suppression | Screens for Cushing's, not pheochromocytoma | N/A | ### Why 24-Hour Urine Metanephrines is Correct **High-Yield:** 24-hour urine free metanephrines and catecholamines is the **gold standard screening test** for pheochromocytoma in incidentalomas because: 1. **Highest sensitivity and specificity** (96–99%) for biochemical diagnosis 2. **Integrates catecholamine secretion over 24 hours** — captures episodic or subtle elevations 3. **Unaffected by posture, stress, or medications** (unlike plasma catecholamines) 4. **Standardized, reproducible** — can be repeated if borderline 5. **Cost-effective** screening modality **Mnemonic: URINE for Incidentaloma** — **U**rinary metanephrines are **I**nitial **R**ecommended **I**nvestigation for **N**eeds **E**xcluding pheochromocytoma. ### Clinical Pearl Even asymptomatic patients with incidentalomas can have pheochromocytoma. Biochemical screening is mandatory because: - Some tumors secrete catecholamines intermittently - Patients may not recognize subtle symptoms (mild tremor, anxiety) - Risk of hypertensive crisis during anesthesia if undiagnosed [cite:Harrison 21e Ch 405; KD Tripathi 8e Ch 12]