Pediatric Solid Pseudopapillary Neoplasm With Aberrant CD31 Expression: A Potential Diagnostic Pitfall.

Solid pseudopapillary neoplasm (SPN) of the pancreas is a rare epithelial tumor with low malignant potential, predominantly affecting young women and only rarely encountered in the pediatric population. Although the prognosis is generally favorable following complete surgical excision, diagnostic challenges may arise due to unusual histomorphology or aberrant immunohistochemical expression. We report the case of a seven-year-old female patient who presented with abdominal pain and vomiting and was found to have a large intra-abdominal mass initially suspected to be of mesenteric origin on imaging. An incisional biopsy revealed extensive necrosis and viable tumor cells with epithelioid morphology, intracytoplasmic lumina, and focal CD31 positivity, raising the possibility of a vascular neoplasm. Following complete surgical excision, histopathological examination demonstrated focal pseudopapillary architecture. Targeted immunohistochemistry showed tumor cell positivity for cytokeratin, nuclear beta-catenin, CD56, dot-like CD99, progesterone receptor (focal), and aberrant focal CD31 expression, with negativity for ERG and other vascular markers, confirming the diagnosis of SPN. The patient subsequently developed metastatic disease and was started on systemic chemotherapy. This case highlights an unusual pediatric presentation of SPN with aberrant CD31 expression, which represents a significant diagnostic pitfall, particularly in limited or necrotic biopsy specimens. Awareness of such atypical immunophenotypic findings, along with careful morphological assessment and use of a comprehensive immunohistochemical panel, is essential to avoid misdiagnosis and ensure appropriate clinical management.