A large right adrenal mass was noted incidentally on an MRI scan of the lumbar spine, which had been performed for other reasons in a 55-year-old non-obese woman. The bright heterogeneous mass (T2-weighted image) measured 6.2 3 6.2 3 4.1 cm and sat like the head of a serpent on the superior pole of the right kidney (A, arrow). Its margins were smooth, but signal intensity was increased on T2 weighting because of high water content. The left adrenal gland was normal.
Endocrine evaluations for Cushing syndrome, primary aldosteron- ism, pheochromocytoma, and Addison disease were all negative. Mammograms and CT scans of the chest, abdomen, and pelvis were normal.
Laparoscopic right adrenalectomy was performed because of the high probability of malignancy or rupture. The tumor was nonencapsulated and weighed 43 g. Serial sectioning showed yellow surfaces with foci of hemorrhage, calcification, and ossification (B). Microscopic examination showed an admixture of mature adipose tissue that contained active bone marrow elements and bone consistent with the pathological diagnosis of myelolipoma (C). The patient was discharged 3 days after surgery.
Adrenal myelolipoma is usually a benign, nonfunctioning tumor that is most commonly found in the right adrenal gland of women aged 40 to 50 years. The size of the tumor suggests malignancy, while the heterogeneous texture on imaging studies suggests benignity. The incidence of adrenal myelolipoma ranges from 0.08% to 0.2% in autopsy studies. Most patients are asymptomatic, because the tumor is nonfunctioning and lacks malignant potential.
The differential diagnosis includes angiomyolipoma and tumor-forming extramedullary hematopoi- esis. The absence of vascular elements and the presence of fat cells in the surgical specimen excluded both conditions from the differential. This case illustrates that even a large adrenal mass may be benign and nonfunctioning. However, surgery is still needed to finalize the diagnosis and to prevent rupture.