benign tumor incidentally discovered on CT usually in older patients
present in 0.2-0.4% of patients based on autopsy series
are never functioning and do not secret any hormones
case reports show that tumors can spontaneously bleed or become necrotic. If they bleed can present symptomatically
key is to recognize the benign nature of these lesions and avoid unnecessary workup for an incidental adrenal mass
CT Findings
most tumors are simply large fatty masses while other tumors have a variable amount of fat visible.
if no fat is present you can not make the diagnosis on CT
foci of calcification not uncommon
although most tumors are 2-4 cm in size others can be 10 cm or greater (20 cm masses have been reported)
MR Findings
findings will vary depending on the amount of fat present but typically are hyperintense on T1-weighted images
Ultrasound
echogenic mass in the adrenal bed
if extensive fat component to tumor then hard to distinguish from the retroperitoneal fat
Pathology
tumor composed of bone marrow elements including myeloid and erythroid cells and fatty elements.
composed of variable amounts of mature adipose tissue
Clinical presentation
usually as an incidental finding
may present with an acute abdomen due to spontaneous hemorrhage (rare)
Differential Diagnosis
adenoma- usually of low CT attenuation but not as much visible fat as a myelolipoma
retroperitoneal liposarcoma- tumors may grow up to adrenal space and simulate a Myelolipoma especially if findings detected on a chest CT where the entire mass is not scanned
renal angiomyolipoma- projected off superior pole of kidney can simulate a myelolipoma
adrenal cyst- cysts are water density and do not contain fat
metastases- metastases are of higher CT attenuation
References
Adrenal Myelolipoma Cyran KM, KenneyPJ, Memel DS et al. AJR 1996;166:395
The natural history and treatment of Adrenal Myelolipoma Han M, BurnettAL, Fishman EK et al J Urol 1997;157:1213
Characterization of Adrenal Masses Using MR Imaging with Histopathologic Correlation Heinz-Peer G, Honigschnabl S, Schneider B et al. AJR 1999;173: 15-22
