MRI findings of angiomyolipoma of the renal sinus in 5 cases.

The magnetic resonance imaging (MRI) appearance of 5 cases of angiomyolipoma (AML) centered in the renal sinus is presented. All cases exhibited similar imaging findings, including well-circumscribed margins, minimal perceived enhancement without soft tissue components, insinuation around the renal collecting system, and localized hydrocalicosis with associated localized renal parenchymal atrophy but without generalized hydronephrosis. Findings in some cases included extension out of the renal sinus and presence of aneurysmal vessels. Although identification of a renal parenchymal defect has been reported to be useful for the differentiation of a large exophytic AML from a perirenal liposarcoma, none of the cases in our series demonstrated this finding on MRI. To our knowledge, there have been only 2 previous reported cases showing the cross-sectional imaging appearance of an AML of the renal sinus without a renal parenchymal defect. In view of the shared and characteristic imaging features of the 5 cases in our series, we believe that the diagnosis of this condition can be strongly suggested by MRI despite the absence of a visible parenchymal defect. While histology remains the only way to definitively establish the diagnosis, the typical imaging appearance of this entity should enable conservative management with follow-up imaging in an asymptomatic patient. In some cases, embolization and needle biopsy could be used to avoid a surgical approach.