Case 34 :
 
What is the diagnosis?
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Imaging Diagnosis:
Bilateral adrenal masses (R >L) with fat elements :
Adrenal myelolipoma.

Discussion:

Adrenal myelolipoma is a rare benign neoplasm composed of mature adipose tissue and a variable amount of hematopoietic elements. Most lesions are small and asymptomatic, discovered incidentally at autopsy or on imaging studies performed for other reasons. The most widely accepted theory, as cited by Meaglia and Schmidt in a 1992 study of the natural history of adrenal myelolipoma, is the existence of metaplasia of the reticuloendothelial cells of blood capillaries in the adrenal gland in response to stimuli such as necrosis, infection, or stress.


Myelolipomas do not undergo malignant transformation. The primary complication, which is uncommon, is spontaneous rupture of the mass, resulting in retroperitoneal hemorrhage. Rupture and hemorrhage also can occur following blunt trauma

The preferred imaging modality is CT, which shows focal fatty density within the mass. MRI also accurately depicts both microscopic and macroscopic fat using chemical shift imaging and explicit fat saturation technique, respectively. CT appearance of myelolipomas depends on their histologic composition. Large amounts of fat often are seen interspersed with higher-attenuation myeloid tissue. The attenuation values are low (-20 to -30 Hounsfield units [HU]), reflecting the mixture of adipose and myeloid elements. The density of the mass may be slightly higher than that of the adjacent retroperitoneal fat secondary to the presence of the myeloid tissue.

 

Reference:
http://www.emedicine.com/radio/topic18.htm