Discussion Author: David A Mosteller
Adrenal myelolipoma is a benign neoplasm composed of adipose tissue and hematopoietic elements that are usually small and asymptomatic. These tumors are generally discovered incidentally at autopsy or imaging studies performed for other reasons (0.08-0.2% at autopsy). Extra-adrenal sites include the pelvis, thorax and retroperitoneum. They are typically unilateral and variable in size from mm to 30cm. There is an equal incidence in males and females with slight predilection in the Caucasian population. These neoplasms typically occur in the fifth to seventh decades, and no death rate is reported in the literature due to the rarity of these tumors.
CT is the imaging modality of choice for these lesions which can be diagnosed macroscopically by focal fatty density within the mass. Occasionally, discrete calcifications can be found in small amounts along with a thin rim of residual adrenal cortex. MRI can also accurately depict both microscopic and macroscopic fat through chemical shift imaging and explicit fat saturation technique. Ultrasound is typically not used for the characterization of adrenal neoplasms, but has been known to find them incidentally.
It is believed that these tumors might represent an extramedullary site of hematopoiesis or that they arise from metaplasia of the reticuloendothelial cells of capillaries in the adrenal gland in response to stimuli (ie. necrosis, infection, stress).
These lesions are usually asymptomatic but might result in complications such as rupture (rare-only 11 reported cases as of 2003), tumor necrosis and retroperitoneal hemorrhage, and mechanical compression from tumor bulk. Myelolipomas do not undergo malignant transformation and they are rarely associated with endocrine disorders. However, Conn’s and Cushing’s syndromes as well as congenital adrenal hyperplasia have been documented in the literature (25 cases reported by one study).
Small asymptomatic tumors are generally monitored clinically while symptomatic lesions are treated by adrenalectomy. Large asymptomatic tumors are occasionally removed surgically to prevent rupture, and transcatheter embolization is used prior to surgery to stop bleeding of ruptured tumors. As most adrenal myelolipomas are small, asymptomatic, and discovered incidentally, surgery is rarely required.
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