Intrahepatic peribiliary perivascular epithelioid cell tumor (PEComa) associated with heterotopic pancreas: A case report

We have documented an intrahepatic peribiliary tumor composed of the rare combination of PEComa and heterotopic pancreas. PEComa was characterized, both histologically and immunohistochemically, by the presence of distinctive perivascular epithelioid cells. The PEComa family includes a wide variety of different entities, such as angiomyolipoma (AML), lymphangioleiomyomatosis (LAM), and clear-cell “sugar” tumors (CCST) [4]. PEComas may also develop in various organ sites, including the liver, kidney, lung, pancreas, gastrointestinal tract, and soft tissue [4]. The presence of the HMB45 antigen has been found to be of value in the diagnosis of renal AML [5] as well as hepatic [6] and pulmonary [7] PEComas. In the current case, the tumor was composed of spindle cells expressing HMB45 and SMA, and it was diagnosed as a PEComa.

Hepatic PEComas occur principally in adults and predominantly in females [1]. Diagnosis of PEComas is, however, problematic. In a previous study, 9 patients incidentally identified as having asymptomatic liver tumors were preoperatively diagnosed on the basis of MRI and their clinical features as 6 hepatocellular carcinomas, 2 adenocarcinomas, and 1 AML [8]. In the current case, the tumor was initially considered an intrahepatic cholangiocarcinoma because of an obstruction of the B2 bile duct and dilatation of its periphery. PEComas vary widely in size ranging from 0.3 to >30 cm in diameter [9]. In 1 of the smallest cases of PEComa, an hepatic tumor of 0.8 cm was incidentally found during an operation for a gastric gastrointestinal stromal tumor (GIST) [10]. The case reported in the present study showed an early-stage tumor of only 3 × 3.8 mm. It is, therefore, difficult to make an accurate preoperative diagnosis of hepatic PEComa and to distinguish those with malignant potential from the benign lesions. Surgical resection with an adequate margin would, however, be the standard and appropriate procedure for the treatment of hepatic PEComa, because the majority of these tumors are benign [11].

Pancreatic PEComas are rare tumors. Twelve cases, with a predominance of tumors in females, have so far been reported [2]. Tumor sizes have ranged from 1.5 to 10 cm. The histopathological characteristics of the tumor cells arising from several organs are not distinguishable [12].

Folpe et al. [13] proposed classifying PEComas into 3 categories including benign, uncertain malignant potential, and malignant. They suggested that malignancy could be predicted by satisfying two or more of the following features: a >5-cm tumor, infiltrative growth, high nuclear grade and cellularity, the presence of >1 mitosis in 50 high-power fields, tumor necrosis, and vascular invasion. Because the present case did not fulfill any of these criteria, it was considered benign. Moreover, the patient has not shown any evidence of tumor recurrence or metastasis during the follow-up period for 56 months.

The presence of heterotopic pancreas in the hepatobiliary system [14] is rare compared with that in the gastrointestinal tract [15]. Indeed, 29 adenocarcinomas have been reported in heterotopic pancreas localized in gastrointestinal tracts [16]. Apart from the report by Yan et al. of an adenocarcinoma in intrahepatic heterotopic pancreas [17], no other tumors have been described as being associated with intrahepatic heterotopic pancreas so far.