A 62-year-old male patient was referred to our hospital because a mass in the head of the pancreas was found 3 months ago at a routine health check. The patient denied nausea, vomiting, jaundice of the skin or sclera, or fever. He had no history of pancreatitis or diabetes. Routine clinical biochemistry showed normal levels of pancreatic amylase, pancreatic lipase, and tumor markers, including carcinoembryonic antigen (CEA) and carbohydrate antigen19-9 (CA19-9). Contrast-enhanced abdominal computed tomography (CT) displayed a 3.9 × 4.6 × 4.5 cm well-defined round mass in the head of the pancreas. The mass was mainly composed of soft tissue, with spotted fat, irregular calcification, and necrosis on the margin, and the solid components were significantly enhanced (Fig. 1a,b). There was no dilation of pancreatic duct and no enlargement of lymph nodes. The magnetic resonance imaging (MRI) showed a spot-like lower signal in the opposed phase image compared to the in phase sequence (Fig. 1c,d). The lesion was firstly misdiagnosed as the pancreatic solid pseudopapillary neoplasm.

Non-enhanced and contrast-enhanced CT (a,b) revealed a tumor in the head of the pancreas, with spotted fat in the center (red arrow), irregular calcification (red arrow head) and necrosis (black arrow) on the margin. Magnetic resonance imaging (MRI) showed spot-like lower signal in the opposed phase image (d) compared to the in phase sequence (c).

The pylorus-preserving pancreaticoduodenectomy, common bile duct reconstruction, and cholecystectomy were performed. On gross examination, the tumor was a gray and white mass with a clear boundary, measuring 5 × 3.5 × 3.9 cm,the cut surface of which was cystic-solid with focal calcification, grayish yellow in color and medium in texture. The major duodenal papilla was not involved. Histopathologic analysis of the specimen showed angiomyolipoma of the pancreas, predominantly in epithelial-like morphology with degeneration. Immunohistochemical staining was positive for CD117(partial), smooth muscle actin, Bcl-2, CD34, Ki-67(index 5%), Melan-A (partial), HMB-45 and Vimentin, and negative for S-100, TFE3, P63 and AE1/AE3 (Fig. 2). The case was finally diagnosed as an epithelioid angiomyolipoma (EAML) of the pancreas.

Histopathologic examination of the tumor (a). Immunohistochemical staining showed HMB-45 expression (b).

Angiomyolipoma is a histologically complex mesenchymal tumor composed of varying proportions of vascular, smooth muscle and mature adipose tissue and may be easily misdiagnosed because of morphological heterogeneity in imaging. Primary angiomyolipoma of the pancreas is exceedingly rare. The previously reported EAMLs of pancreas were benign, but the potential of malignancy was not ruled out. Surgery is recommended for the disease. EAML is easily misdiagnosed as other tumors of pancreas, like pancreatic solid pseudopapillary neoplasm and pancreatic neuroendocrine neoplasm. Pancreatic solid pseudopapillary neoplasm typically occurs in young women, which is a cystic-solid tumor, often combined with hemorrhage, necrosis and calcification. Pancreatic neuroendocrine neoplasm is rich in blood supply, whose solid component can be enhanced obviously in arterial phase. Imaging detection of the EAML is mainly based on chemical shift imaging for the accurate identification of the fat. Whenever the fat is appeared, the pancreatic primary angiomyolipoma should be taken into account.