Malignant Gastrointestinal Stromal Tumor: Distribution, Imaging Features, and Pattern of Metastatic Spread

PURPOSE: To investigate and describe the anatomic distribution, imaging features, and pattern of metastatic spread of malignant gastrointestinal stromal tumors (GISTs). MATERIALS AND METHODS: The medical records of all patients at our institution with a histologic diagnosis of GIST were reviewed. Two radiologists with knowledge of the diagnosis reviewed the radiologic findings by means of consensus. Sixty-seven patients underwent computed tomography, and scans of the primary tumor were available in 38 patients. RESULTS: One hundred sixteen patients with malignant GISTs were identified (76 men and 40 women; mean age, 54.6 years +/- 13.5 SD). The primary tumor locations in descending order of frequency were the small bowel (n = 49), stomach (n = 43), colon (n = 7), rectum (n = 6), other (n = 3), and not specified (n = 8). Mean primary tumor size was 13 cm +/- 6. Tumors were typically well defined (31 of 36 86%), with a heterogeneous rim of soft tissue with lower signal intensity than that of the contrast material-enhanced liver. Central fluid attenuation was seen in 24 of 36 (67%) patients. Metastases were seen in 23 of 38 (61%) patients at presentation and in 53 of 61 (87%) patients during follow-up. Spread was usually to the liver or peritoneum. Visceral obstruction rarely occurred, even in the presence of extensive peritoneal metastatic disease. Ascites was an unusual finding. CONCLUSION: Malignant GISTs are typically large, well-circumscribed, heterogeneous, centrally necrotic tumors that arise in the wall of the small bowel or stomach. They rarely obstruct viscera, despite their large size and propensity to metastasize to the liver and peritoneum.