Epithelioid Angiomyolipoma: An Overview of Five Cases with the Concept of PEComa

Angiomyolipoma is a well-known rare soft tissue tumor involving the kidneys, liver and other organs. Long believed to be a benign hamartoma, angiomyolipoma is now considered a neoplasm that arises from perivascular epithelioid cell. Epithelioid angiomyolipoma is potentially malignant variant of angiomyolipoma characterized by epithelioid cells that mimic mal ignant tumors arising from the organs. Immunoreactivity with HMB-45 is helpful for its identification. It is now considered to be a part of PEComa family and perivascular epithelioid cells (PEC) are recently proposed to be its most common progenitor cells. Here we give an overview of five rare cases with epithelioid angiomyolipoma, one in left upper retroperitoneum, two in liver and two in kidney, focusing on clinical presentations and imaging findings. The case in left upper retroperitoneum was pre-operative differentiated from retroperitoneal liposarcoma due to huge space-occupying lesion of uncertain origin. The two cases in kidneys were clinically manifested as palpable abdominal mass and/or acute abdominal pain; both were pre-operative diagnosed by tumoral fat content and/or the classic clinical features. One case with maliganant epithelioid angiomyolipoma of kidney associated with tuberous sclerosis (TS) developed metastases to liver and retroperitoneum and finally died of the disease. The two cases of hepatic epithelioid angiomyolipoma were pre-operative misdiagnosed as hepatocellular carcinoma (HCC) due to its rare incidence and less fat component of the tumor with similar imaging finding to HCC. In conclusion, we radiologists should be aware of the existence of rare epithelioid variant of angiomyolipoma which belongs to the PEComa family arising in different origins and its potential malignant behavior.