Abstract
Gastrointestinal stromal tumors (GIST) typically appear as solid masses, and cystic formation is uncommon. Most stomach GISTs with cystic formation progress outside the gastric wall and are frequently misdiagnosed as epigastric cystic tumors derived from pancreas or liver. An asymptomatic 72-year-old male underwent esophagogastroduodenoscopy, which revealed a submucosal tumor (SMT), approximately 50 mm in diameter, at the anterior wall of the gastric angle. The SMT was very soft with positive cushion sign. Endoscopic ultrasonography and contrast-enhanced computed tomography revealed that the SMT was a cystic tumor with solid component. Laparoscopic and endoscopic cooperative surgery were performed to remove the tumor. Histopathological analysis revealed that the tumor was a GIST with cystic formation. To the best of our knowledge, this the first documented case of a cushion sign-positive stomach GIST with cystic formation, which had mainly developed inside the stomach. This case suggests that we should keep in mind the possibility of cystic formation of GIST when the tumor has a solid component, even if it appears as a cushion sign-positive SMT.