Retroperitoneal Liposarcoma With Intrarenal Metastases Which Was Difficult to Distinguish From Angiomyolipoma

A 40-year-old man was admitted to our hospital with a fat-density extrarenal tumor and intrarenal nodules which were detected by ultrasonography (US) and CT scan obtained the general health check. After his admission, US, CT, MRI and angiography were performed. As the final diagnostic procedure, we performed a US-guided percutaneous needle biopsy of the extrarenal tumor, because this tumor was difficult to distinguish from liposarcoma and angiomyolipoma (AML). The pathological study revealed a well-differentiated liposarcoma, and the extrarenal tumor and the left kidney were removed en bloc. Pathologically, the tumor not only invaded into the renal parenchyma directly but also have metastasized independently to the intrarenal region. Postoperatively, he received a tumor dose of irradiation of 50 Gy. Liposarcoma arising in the perirenal space should be considered in the differential diagnosis of exophytic AML. If radiological studies can not confirm the appropriate diagnosis, we consider that biopsy of the tumor should be selected as an alternative diagnostic approach. And, we think that this is the first case report dealing with intrarenal metastases of liposarcoma.