SUN-487 - Large Adrenal Endothelial Cyst Masquerading Malignancy

Background:
Adrenal cysts are rare lesions, with a reported incidence of 0.064%–0.18%. Most are discovered incidentally on abdominal imaging as they are typically asymptomatic. Cystic adrenal lesions include pseudocysts, endothelial cysts, mesothelial cysts, cortical adenomas, cystic pheochromocytomas, and metastatic cystic lesions. Although most are small and benign, large cystic adrenal masses raise concern for malignancy and often require surgical evaluation.

Case Presentation:
A 58-year-old man with a history of T2DM, HFrEF secondary to ischemic cardiomyopathy, HTN, osteoarthritis, and nicotine dependence underwent CT imaging of the abdomen in the emergency department for constipation. Imaging revealed an incidental heterogeneous,13-cm left adrenal mass with peripheral calcifications. Personal and family history were negative for malignancy or adrenal disease. Patient had unintentional 40-lb weight loss over 8 months and intermittent constipation but no episodic headaches, palpitations, diaphoresis, fever, or night sweats.

Biochemical evaluation included dexamethasone suppression testing, 24-hour urine cortisol, metanephrines, plasma free metanephrines, CMP, ACTH, DHEA-S, aldosterone, plasma renin activity. Results were within normal limits, supporting a nonfunctional adrenal mass without biochemical evidence of cortisol excess or pheochromocytoma.

After cardiac clearance, the patient underwent robotic-assisted left adrenalectomy due to the large size of the lesion and concern for malignancy. Intraoperatively, the mass had a clear plane from the kidney and appeared non-infiltrative. Pathology revealed a 14 × 14 × 9.7 cm encapsulated mass weighing 925 g. Microscopy demonstrated calcified degenerative material and fibrin within the cyst with a fibrotic, inflamed, and calcified cyst wall containing adrenal tissue, consistent with an adrenal endothelial cyst.

Postoperatively, the patient developed hypotension and bradycardia with a random cortisol of 0.5 µg/dL at 5 PM. Intravenous hydrocortisone was initiated followed by an oral taper, resulting in hemodynamic improvement. Patient was tapered off hydrocortisone after discharge and adrenal insufficiency was ruled out.

Conclusion:
Endothelial adrenal cysts represent approximately 45% of adrenal cysts on autopsy. They are typically simple lesions and measuring less than 2 cm. Large adrenal lesions, more than 10 cm are uncommon and may mimic malignant adrenal tumors on imaging. Careful biochemical evaluation is essential to exclude functional disease prior to surgery. Surgical resection for large lesions are recommended for definitive diagnosis and curative management.

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