Solid-pseudopapillary neoplasm of the pancreas: awareness of unusual clinical presentations and morphology of the clear cell variant can prevent diagnostic errors.

Solid-pseudopapillary neoplasm (SPN) of the pancreas is a rare neoplasm predominantly reported in young women. It classically presents as a large tumor with cystic and solid components. The major differential diagnosis includes pancreatic neuroendocrine tumor (PanNET). This study presents our experience with this tumor with emphasis on the morphologic features of the clear cell variant of SPN. Fifteen histologically confirmed SPN were identified in our files. Endoscopic ultrasound-guided fine needle aspirations (EUS-guided FNA) were performed in 8/15 cases. Patients' demographics, cytohistologic correlation and tumor characteristics were evaluated. Eleven of the 15 subjects were female and four were male with an age range of 17-73 years. Twelve SPN were located in the pancreatic body/tail, and three in the head. Tumor size ranged from 1.5 to 8.5 cm and 11 were solid. Of the eight EUS-guided FNA, four were diagnosed as SPN, two as SPN vs. PanNET, one as malignant with signet ring features, and one was nondiagnostic. Immunohistochemistry was performed on six/eight FNA cell blocks and 13/15 surgical specimens. Two of the 15 cases were classified as clear cell variants of SPN. Our study shows that SPN may occur in males and older adults, and present as a small or solid tumor. The clear cell variant of SPN, characterized by vacuolated cytoplasm and signet cell morphology, may pose a diagnostic challenge on FNA. Awareness of the wide spectrum of SPN clinical presentations, the morphology of its clear cell variant and the appropriate use of ancillary immunohistochemistry can prevent diagnostic errors.