Solid pseudopapillary neoplasm: pathological diagnosis and distinction from other solid cellular tumours of the pancreas

Solid pseudopapillary neoplasm (SPN) is a rare pancreatic tumour with low malignant potential. It is clinically distinct from other pancreatic tumours, and the proper diagnosis is crucial for patient management. However, the histological features of SPN are variable and its diagnosis is not always straightforward. Finger-like extension of the tumour into the surrounding pancreatic parenchyma, a perpendicular cell arrangement around blood vessels and indented vesicular nuclei are characteristic histological features of SPN. The lobulated solid cell pattern seen in SPN is easily mistaken for pancreatic endocrine tumour. Immunohistochemically, SPN is consistently positive for vimentin and CD56, negative or focally positive for cytokeratin and synaptophysin, and always negative for chromogranin. Diffuse nuclear expression of β-catenin is useful for the diagnosis. The distinction of SPN from other solid cellular neoplasms can be made by careful histological observation as well as using a panel of immunohistochemical markers.