Imaging and pathologic features of myelolipoma.

Myelolipoma is a benign tumor consisting of mature fat interspersed with hematopoietic elements resembling bone marrow. Imaging findings in a large series of pathologically proved cases of myelolipoma were correlated with the pathologic and histologic features of the lesions. Myelolipoma manifests in four distinct clinicopathologic patterns: isolated adrenal myelolipoma, adrenal myelolipoma with hemorrhage, extraadrenal myelolipoma, and myelolipoma associated with other adrenal disease. Myelolipoma is difficult or impossible to detect at plain radiography unless the lesion is large and predominantly fatty. At ultrasound, myelolipoma often has heterogeneous echogenicity due to its typically nonuniform architecture. Computed tomography (CT) frequently demonstrates large amounts of fat with areas of interspersed higher-attenuation tissue. At magnetic resonance imaging, predominantly fatty areas usually have increased signal intensity on T1-weighted images and moderate hyperintensity complicated by the presence of marrowlike elements in the corresponding regions on T2-weighted images. The imaging appearance of myelolipoma is altered by the presence of hemorrhage. In such cases, CT is the most accurate method for evaluation. Knowledge of the imaging characteristics of myelolipoma usually allows presumptive diagnosis, although percutaneous needle biopsy may be needed to confirm the diagnosis in cases of extraadrenal myelolipoma. Surgical excision is unnecessary unless the diagnosis is unclear or the lesion is symptomatic. Asymptomatic, nonhemorrhagic myelolipomas do not require therapy.