Presentation
Right flank pain. A right retroperitoneal mass lesion was noted on sonography for assessment.
Patient Data
A large retroperitoneal right suprarenal mass lesion with mixed densities. It shows areas of gross fat content (macroscopic fat) with low density mixed with otherwise soft tissue density components. It is oval in shape with smooth macrolobulated contour at the anatomical site of the right adrenal gland. It is displacing the right kidney downwards.
Normal CT features of the left adrenal gland.
A large right suprarenal mass lesion is noted, measuring 10 x 7 cm. It shows ovoid shape, smooth contours, and mixed signal, predominantly gross fat that appears of high signal on T1WI and T2WI. The fat contents are suppressed in fat sat sequences and show drop of signal in T1 out of phase sequence. The non-fatty component shows contrast enhancement.
Normal size and imaging features of the left suprarenal gland.
Case Discussion
The described lesion shows almost most of the typical imaging criteria of the classic adrenal myelolipoma. It is a benign adrenal tumor that is usually incidentally noted with macroscopic fat content. It can be bilateral or unilateral with a right side predilection. It is often hormonally inactive lesion
On CT, the presence of fat densities in a benign looking suprarenal mass lesion is the key for the diagnosis. The non-fatty soft tissue component usually enhances due to hematopoietic tissue composition.
On MRI, it shows fat suppression and loss of signal on T1 out of phase imaging as the macroscopic fat lacks intracellular water. Rarely, it can cause retroperitoneal hemorrhage. The lesion is usually an admixture of soft tissue and fat, however, it can appear as a complete fatty lesion.
Other suprarenal neoplasms can show macroscopic fat, but fat-containing malignancies of the adrenal gland are exceedingly rare, like fat-containing adrenal cortical adenoma / carcinoma. Other fat-containing retroperitoneal tumors also could be regarded like lipomas, angiomyolipomas, mature teratomas, and liposarcomas that should be differentiated so.
Percutaneous fine-needle aspiration by US or CT guidance can confirm the diagnosis.
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