A duodenal gastrointestinal stromal tumor with a large central area of fluid and gas due to fistulization into the duodenal lumen, mimicking a large duodenal diverticulum.

Gastrointestinal stromal tumors (GISTs) can occur anywhere along the gastrointestinal tract especially the stomach and upper small bowel. They are usually solid, but cystic degeneration, necrosis, and focal hemorrhage have been described in larger tumors leading to central necrotic cavitation. The most sensitive marker of GIST is CD117 (c-kit).