470 Synchronous Gastrointestinal Stromal Tumor and AV Malformation of the Jejunum: A Diagnostic Challenge

Introduction/Objective Gastrointestinal stromal tumors (GISTs) are mesenchymal neoplasms arising from interstitial cells of Cajal, typically affecting the gastrointestinal tract. Arteriovenous (AV) malformations in the bowel are uncommon but can cause significant bleeding. The simultaneous occurrence of GIST and AV malformation in the small intestine is exceedingly rare. Methods/Case Report We report a 53-year-old female presenting with abdominal pain and liver abscess. CT imaging revealed an incidental hyperenhancing lesion abutting the small bowel, raising concern for neuroendocrine tumor. Small bowel resection identified a firm, round jejunal mass (2.8 x 2.2 x 1.8 cm) with a tan-brown, homogeneous cut surface and cystic changes. Histologically, the tumor showed mixed spindle and epithelioid cells in fascicles and lobules. Prominent, variably dilated vessels intermingled with tumor cells in the submucosa and subserosa. Immunohistochemistry was diffusely positive for CD117 and DOG1, focally positive for CD34 and SMA, and negative for Desmin and S100. Elastin staining highlighted an adjacent AV malformation. Findings aligned with synchronous GIST and AV malformation. Results N/A Conclusion This case highlights a rare coexistence of jejunal GIST and AV malformation, with few cases in the literature. It emphasizes the critical role of careful histopathologic evaluation in accurately diagnosing and differentiating such complex lesions from other small bowel neoplasms.