SUN-495 - Beyond the Incidentaloma: A Silent Pheochromocytoma Unmasked on CT

INTRODUCTION

Adrenal incidentaloma is a mass detected on imaging performed for investigation of another issue. Incidentalomas are most often benign but warrant evaluation for hormone hypersecretion and malignancy risk. Pheochromocytomas are rare adrenal tumors that may present without the classic symptom triad of episodic headaches, palpitation and diaphoresis, yet can cause significant morbidity and mortality if unrecognized.

CASE REPORT

A 60-year-old woman with hypertension (on lisinopril 20mg and HCTZ 25mg) and diabetes was referred to endocrinology after a 4.7 cm heterogenous left adrenal mass was incidentally noted on CT obtained for evaluation of abdominal pain. She had no headaches, palpitations or excessive sweating. Her blood pressure was 158/114 mmHg, physical examination was unremarkable. Laboratory testing showed markedly elevated free plasma metanephrines 342 pg/ml (normal < 57) and normetanephrines 1096 pg/ml (normal < 148), with normal dexamethasone suppression test, aldosterone, renin, and DHEAS. These findings established the diagnosis of pheochromocytoma, prompting initiation of alpha-adrenergic blockade with phenoxybenzamine 10 mg twice daily, which was discontinued due to severe headaches and nasal congestion, and subsequently replaced with doxazosin 4 mg daily with improved blood pressure control. PET scan excluded metastatic disease. After one month, metoprolol 25 mg daily was added to achieve combined alpha and beta blockade prior to surgery, and three weeks later the patient underwent successful laparoscopic left adrenalectomy with histology confirming pheochromocytoma. Postoperatively, her blood pressure normalized on lisinopril 20 mg daily alone, plasma metanephrines and normetanephrines returned to normal range, and she was referred for genetic testing according to current guidelines.

DISCUSSION

European Society of Endocrinology guidelines emphasize adrenal imaging characteristics like homogeneity and unenhanced CT Hounsfield units to stratify malignancy risk and guide management of adrenal incidentalomas. All patients with adrenal incidentalomas should undergo endocrine evaluation, including plasma or urinary metanephrines and dexamethasone suppression testing, to detect pheochromocytoma and mild autonomous cortisol secretion, which are associated with increased cardiovascular and metabolic risk. Surgical intervention is recommended for hormonally active tumors and lesions with imaging features suspicious for malignancy. Surgery is not indicated for asymptomatic, nonfunctioning unilateral adrenal masses with benign radiologic features.

CONCLUSION

This case highlights that all adrenal incidentalomas, especially in hypertensive patients, can harbor clinically silent pheochromocytoma and require endocrine workup, appropriate preoperative management to reduce perioperative morbidity and mortality.

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