## Diagnostic Approach to Pheochromocytoma ### Clinical Presentation The patient presents with the classic triad of pheochromocytoma: - Episodic hypertension with severe elevations - Profuse sweating and palpitations - Tremor and anxiety Elevated 24-hour urine metanephrines confirm catecholamine excess. ### Investigation Hierarchy **Key Point:** After biochemical confirmation (elevated plasma free metanephrines or 24-hour urine metanephrines), the next step is **anatomical localization**, not further biochemical testing. | Investigation | Purpose | Timing | |---|---|---| | Plasma/urine metanephrines | Biochemical diagnosis | First-line | | CT/MRI abdomen-pelvis | Anatomical localization | After biochemical confirmation | | 123I-MIBG scintigraphy | Functional imaging, detect metastases | If CT/MRI negative or for staging | | Clonidine suppression | Rarely used, only if biochemistry equivocal | Not standard | ### Why CT Abdomen-Pelvis is Correct **High-Yield:** CT with IV contrast is the **investigation of choice for localization** of pheochromocytoma after biochemical confirmation. It has: - High sensitivity (90–95%) for tumors >1 cm - Excellent spatial resolution for adrenal and extra-adrenal sites - Rapid acquisition - Guides surgical planning **Clinical Pearl:** Pheochromocytomas are typically hyperdense on contrast-enhanced CT due to high catecholamine content and vascularity. ### Sequence of Investigations 1. Biochemistry (plasma free metanephrines or 24-hour urine metanephrines) — **already done** 2. **Anatomical imaging (CT/MRI)** — **next step** 3. Functional imaging (123I-MIBG) — if CT negative or for metastatic staging 4. Genetic testing — if syndromic features or familial history [cite:Harrison 21e Ch 405]
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