A 52-year-old man with a 10-year history of hypertension presents with episodic severe headaches, profuse sweating, and palpitations lasting 20–30 minutes. Blood pressure during an episode is 210/120 mmHg; baseline is 160/95 mmHg. Plasma metanephrines are elevated. Which investigation is most appropriate to confirm the diagnosis and localize the lesion?

## Diagnosis: Pheochromocytoma The clinical presentation—episodic hypertension with classic triad of headache, sweating, and palpitations—combined with elevated plasma metanephrines strongly suggests pheochromocytoma. Once biochemical diagnosis is confirmed, **anatomical localization** is the next critical step. ## Investigation of Choice: CT Abdomen with Contrast **Key Point:** After biochemical confirmation (plasma or 24-hour urine metanephrines), **CT abdomen with IV contrast** is the first-line imaging modality to localize the tumor. - Sensitivity ~95% for adrenal pheochromocytomas - Excellent spatial resolution for masses >1 cm - Can detect extra-adrenal tumors (paragangliomas) along the sympathetic chain - Rapid and widely available ## Why CT Over Other Imaging? **High-Yield:** MRI is equally sensitive but slower and less accessible in acute settings. MIBG scintigraphy is reserved for metastatic disease or when CT/MRI is inconclusive. PET-CT is not first-line. ## Clinical Pearl Contrast-enhanced CT can differentiate pheochromocytoma from benign adrenal adenoma by assessing washout characteristics (pheochromocytomas retain contrast longer). Always obtain imaging **before** any invasive procedure (biopsy, angiography) to avoid catecholamine release. ## Biochemical Confirmation Sequence ```mermaid flowchart TD A[Clinical suspicion: episodic HTN + symptoms]:::outcome --> B[Plasma metanephrines or 24h urine metanephrines]:::action B --> C{Elevated?}:::decision C -->|Yes| D[Biochemical diagnosis confirmed]:::outcome D --> E[CT abdomen with contrast]:::action E --> F[Tumor localized]:::outcome C -->|No| G[Pheochromocytoma unlikely]:::outcome ```