Endoscopic ultrasound-guided fine needle aspiration diagnosis of a focal fatty mass in the pancreas.

Focal fatty masses of the pancreas, which include focal fatty infiltration, lipoma, and liposarcoma, are rare entities [1]. A well-differentiated lipogenic liposarcoma can mimic a benign lesion on radiologic examination and only cytohistology can resolve the doubt [2]. A 60-year-old woman was referred to our department because of an incidental ultrasound diagnosis of a lesion in the head of the pancreas. The patient was asymptomatic. An unenhanced computed tomography (CT) scan showed a 43-mm homogeneous, hypodense lesion at the pancreatic head (●" Fig.1a). Abdominal magnetic resonance imaging (MRI) showed the lesion tobehypointenseon fast imagingemploying steady-state acquisition (FIESTA) with fat saturation (●" Fig.1b) and hyperintense on T2-weighted fast-spin echo (FSE) acquisition without fat saturation (●" Fig.1c). No clear contact with abdominal fat was seen. An endoscopic ultrasound (EUS) showed a lobulated, ill-defined, heterogeneous lesion, which was slightly hypoechoic compared with the surrounding pancreatic parenchyma but with internal hyperechoic strands (●" Fig.2a). The appearance was compatible with both a pancreatic lipoma and focal fatty infiltration, but even a liposarcoma could not be excluded. For this reason, we decided to perform an EUSguided fine needle aspiration (FNA) with a 19-gaugeneedle (onepassage) (●" Fig.2b), which revealed clearly visible fat globules on the smears (●" Fig.3a). Cytohistologic examination showed mature adipocytes characterized by large fat droplets and eccentrically placed small nuclei without atypia. The adipocytes were interspersed with islands of normal pancreatic tissue (●" Fig.3b,c). Immunohistochemical staining for Ki-67 showed no mitotic activity (●" Fig.3d). This focal fatty mass of the pancreatic head had some of the characteristics of a lipoma (no clear contact with abdominal fat on imaging), and some of focal fatty infiltration (no clear cytohistologic demarcation from pancreatic parenchyma) [1, 2]. This difficulty in distinguishing between these nosologic entities has been previously reported, but a clear distinction is not necessary because conservative treatment is indicated for both types of lesion. EUS-FNA, on the other hand, permits clear classification of such lesions where the differential diagnosis includes liposarcoma, which has a surgical indication. Only three other cases of EUS-FNA of a focal fatty mass of the pancreas have been reported [3–5], but considering the