A case of angiomyolipoma of the renal sinus.

The case of a 63-year-old woman with a relatively rapidly growing angiomyolipoma (AML) originating from the right renal sinus is presented. The tumor had enlarged to more than fivefold in volume (7.4 × 6.7 × 10.1 cm) in the 7 years following its detection (5.6 × 3.4 × 4.6 cm) and had significantly pushed aside the duodenum and the inferior vena cava. The tumor was surgically resected together with the right kidney, and pathological examination revealed AML originating from the renal sinus. An AML involving or originating from the renal sinus is exceedingly rare; only 14 cases have been reported. Rapidly growing AMLs of the renal sinus are difficult to differentiate from liposarcoma because of similar findings in imaging studies. It should be noted that AML of the renal sinus can be a differential diagnosis of retroperitoneal fatty mass. Furthermore, an enlarged AML in the renal sinus may push aside other organs, such as the ileum, pancreas, and major vessels. Clinicians should determine whether these patients should be placed under active surveillance or be treated with invasive measures, such as radical nephrectomy.