Adrenal myelolipoma is an uncommon, benign, endocrinologically inactive tumor of unknown pathogenesis composed of adipose and myeloid tissue. Majority of the lesions are detected incidentally. In most lesions, the fatty component is predominant and is recognizable on radiologic images. Such lesions are radiolucent on radiographs, hyperechoic on sonograms, have low attenuation on CT scans, and have bright signal intensity on T1 -weighted MR images and intermediate signal intensity on T2- weighted MR images.
Tumors composed primarily of myeloid tissue may be hypoechoic on sonograms and will have the imaging characteristics of red marrow on other kinds of images. In complicated cases in which infarction or hematoma is present, the margins of the lesions may be irregular and infiltrative, with blood dissecting through the retroperitoneum. The imaging findings of acute, subacute, or chronic hematoma will then be superimposed on the lesion. When lesions are fatty, well marginated, uncomplicated, and in the position of the adrenal gland, a specific radiologic diagnosis is possible. However, the mere presence of fat in an adrenal mass is insufficient for diagnosis, because a metastasis or other aggressive lesion may engulf fat as it spreads. Nonspecific calcification may sometimes present.