Most pancreatic tumors arise from epithelial cells. In fact, only 1 to 2% of these tumors originate from the mesenchyme. Mesenchymal tumors are classified according to histologic origin and include benign and malignant neoplasms. Because pancreatic lipomas can be observed if there is no specific clinical symptom or change in tumor size, the histologic confirmation of pancreatic lipoma is rare. However, when the pancreatic tumor is symptomatic and difficult to distinguish from well-differentiated liposarcoma, surgical management would be needed. We report a large pancreatic lipoma with histologic confirmation which was difficult to distinguish from a liposarcoma.

A 54-year-old male patient with type 2 diabetes mellitus was evaluated for assessment of an incidental pancreatic tumor. There were no specific findings based on laboratory testing (amylase, 84 IU/L; lipase, 23 IU/L; carcinoembryonic antigen, 1.86 ng/mL; carbohydrate antigen 19-9, 12.78 U/mL), with the exception of an elevated glucose level (172 mg/dL). Computed tomography (CT) demonstrated a 9-cm, well-circumscribed, non-invasive tumor in the body of the pancreas with a -100 HU density which was homogeneous in appearance with the fat composition of the abdominal wall (Fig. 1A). Although the initial impression was a lipoma, a liposarcoma could not be completely ruled out because of a focal enhancing soft tissue component in the mass. On magnetic resonance imaging, there was a 10.5 cm well-defined, hyperintense mass containing mural nodules in the body and tail of the pancreas on axial T1-weighted images (Fig. 2). After 3 months, a subtotal pancreatectomy with a splenectomy was performed to distinguish the mass from a liposarcoma because the pancreatic tumor increased from 9 to 10.5 cm in size on contrast-enhanced abdominal CT (Fig. 1). In pathologic finding, a 10.4 × 6.9 cm pancreatic lipoma containing yellow focal fibrous tissue and hemorrhagic areas was identified which was suggested as a mural nodule on image findings. Based on the microscopic findings, only mature adipocytes were noted adjacent to the pancreatic parenchyma (Fig. 3). Post-operatively, the patient was treated to control a worsening glucose level and discharged without specific complications in 14 days.

Since the first pancreatic lipoma was documented by Bigard et al. [1] in 1989, only 45 cases of pancreatic lipomas have been reported. Although the tumor size could vary from <1 to 30 cm in size, the observation would be possible because they are nearly stable. For this reason, the histologic confirmation of pancreatic lipoma is rare [2-9].

While lipomas located with the head of the pancreas may originated from trapped retroperitoneal or mesenteric fat between the dorsal and ventral pancreatic buds during embryonic fusion, the etiopathogenesis of lipomas within the body and tail of the pancreas are unclear [10]. Lipomas within the head of the pancreas exhibit clinical symptoms, such as abdominal pain, whereas lipomas within the body and tail of the pancreas are usually silent, even when >10 cm in size (Table 1) [1-9].

A CT scan is a useful imaging modality for detecting pancreatic lipomas. The diagnostic criteria for pancreatic lipomas include well-circumscribed lesions without any extravisceral continuation with the peri-pancreatic adipose tissue, densitometric measurement between -30 and -150 HU, well-delineated thin-homogenous capsule, and no sign of invasion of adjacent organs. The thick septa within the tumor, calcifications, rapid growth, and focal fatty infiltration within the peri-pancreatic adipose tissue, in contrast to pancreatic lipomas, and the absence of distinct capsules are significant indicators of malignancy [10]. A surgical procedure is needed for well-differentiated liposarcomas which resemble benign lipomas [1]. The differential diagnosis of pancreatic lipomas should include lipomatosis, cystic teratomas, fibrolipomas, lipoblastomas, and liposarcomas. In the current case, liposarcomas could not be ruled out because of the increasing size and enhancing soft tissue component. An endoscopic ultrasoundguided fine-needle aspiration (EUS-FNA) was not performed because EUS-FNA sometimes leads to needle-track seeding metastasis when the mass is malignant.

There are 10 histologically-confirmed lipomas based on surgical resection or EUS-FNA, including the current case (Table 1). The mean size of 8 pancreatic lipomas confirmed with surgery was 10.5 cm and the locations of the tumor were as follows: 6 cases in the head of the pancreas; 1 case in the body of the pancreas; and 1 case in the tail of the pancreas. Abdominal pain was associated with most pancreatic lipomas and pancreatitis occurred in two cases, but not in the current case.

Although pancreatic lipomas are not common, the diagnosis with imaging scans is quite accurate and EUS-FNA is a useful procedure for histologic confirmation of the tumor. Surgical excision should be considered when the tumor is symptomatic or difficult to distinguish from a liposarcoma.