A Mass in Disguise: A Rare Case of High-Attenuation Adrenal Myelolipoma

Abstract

Abstract Background: Adrenal incidentalomas are common, and imaging studies play a large role in reaching the diagnosis in many cases. Adrenal myelolipomas are classically diagnosed by CT as a hypodense well circumscribed heterogenous mass with low attenuation. Clinical Case: A 51-year-old man with history of resistant hypertension presented with neck pain after a motor vehicle crash. After a cervical X-ray revealed an odontoid fracture, a whole body CT was obtained. The CT incidentally identified a massive heterogeneous left adrenal mass measuring 22.3 × 15.5 × 20.6 cm, with multiple attenuation measurements ranging from 20 to 53 Hounsfield units (HU). The patient’s physical examination and hormonal assessment were both unrevealing, with normal catecholamine, androgen, and an unremarkable renin aldosterone ratio. Inpatient urinary cortisol levels were elevated, however a repeat urinary cortisol as an outpatient weeks after repair of the odontoid fracture showed normal levels, suggesting physiologic stress response. Positron emission tomography showed a metabolically inactive adrenal mass without metastatic diseases. The patient eventually underwent a left adrenalectomy, and pathology revealed a myelolipoma measuring 24.2 × 20.5 × 8.3 cm. Imaging characteristics for adrenal incidentalomas are considered useful diagnostic information according to most clinical guidelines. Lesions with high HU are typically pheochromocytomas, adrenocortical carcinoma, metastatic disease, or lipid poor adenomas. Myelolipomas are identified on CT by their characteristically low HU (often -30). In this case of a massive myelolipoma with high HU, the unique imaging characteristics posed a diagnostic challenge. The patient’s history of resistant hypertension combined with the high HU led to the patient undergoing extensive testing for a functional mass or cancer. Conclusion: This is a rare case of a massive myelolipoma with low attenuation. The role of imaging studies in the diagnosis of adrenal incidentalomas is not definitive, and detailed exam along with hormonal assessment may be warranted in atypical cases. Providers should consider myelolipoma in the differential diagnosis of a large adrenal mass with a negative hormonal evaluation even in the setting of high HU.