Gut wall replacing type of gastrointestinal stromal tumor presenting as a perforation of the ileal diverticulum.

Gastrointestinal stromal tumors (GISTs) usually form a well-circumscribed mass. Very rarely, however, sporadic GISTs show gut-wall replacing growth, similar to the diffuse hyperplasia of interstitial cells of Cajal (ICC) observed in patients with neurofibromatosis type 1 (NF1) and hereditary GIST. Here we describe a patient with ileal perforation caused by this unusual type of GIST. An 82-year-old man was admitted to the emergency department with sudden abdominal pain. Following a provisional diagnosis of perforation of Meckel's diverticulum, he underwent segmental resection of the small intestine. Macroscopic examination revealed a diverticulum-like structure 2.5cm in size near the site of mesenteric attachment of the ileum. Histological examination showed diffuse and nodular proliferation of spindle cells positive for c-KIT and CD34 that had replaced the muscularis propria of the small intestine. Mutational analyses of the lesions revealed monoclonality of proliferating cells with a somatic mutation in c-kit exon 11 (p.Leu576Pro). Gut-wall replacing type of GIST should be recognized as a specific type of GIST causing diverticulum-like structures of the gastrointestinal tract.