Applied Radiology

Diagnosis

Gastrointestinal stromal tumor

Findings

Contrast enhanced axial computed tomography (CT) images demonstrate a large volume of free intraperitoneal air. There is a heterogeneous, mildly enhancing lesion with an exophytic growth pattern arising from the fundus of the stomach. The lesion demonstrates areas of low density, likely representing necrosis. Foci of gas are seen throughout the mass with a tract extending from the fundus of the stomach to the peritoneum. The tract contains gas as well as a small amount of oral contrast material. The remainder of the stomach is normal in appearance.

Discussion

Gastrointestinal stromal tumors (GIST) are the most common mesenchymal tumor of the gastrointestinal tract and are believed to originate from the interstitial cells of Cajal. There are four tumor subtypes including benign and malignant spindle cell GISTs as well as benign and malignant epithelial GISTs. Most GISTs occur sporadically but are associated with Neurofibromatosis Type 1 (NF1) and Carney Triad. Studies have shown that up to 25% of patients with NF1 will have GISTs at autopsy. They are rare before the age of 40.

GISTs may occur anywhere within the GI tract with approximately two-thirds of cases located within the stomach and the majority of the remainder occurring within the small bowel. Interestingly, in patients with NF1 small bowel GISTs outnumber gastric GISTs. GISTs are submucosal masses, which are generally well circumscribed and grow exophytically from the GI tract, often becoming quite large. Necrosis and ulceration are very common and approximately 25% will demonstrate calcifications, best seen on CT. Enhancement characteristics are variable, but the solid components usually enhance while the necrotic portions are hypovascular. On MRI, GISTs are generally isointense to adjacent bowel on T1-weighted images, with variable signal intensity on T2-weighted images. PET-CT is often used for malignant GISTs as both the primary tumor and metastases tend to be hypermetabolic. PET-CT also may be used to predict early response to Gleevec.

Treatment consists of en bloc resection with an excellent prognosis for completely resected benign tumors. However, malignant GISTs may invade adjacent organs making complete resection difficult or impossible. Metastases most commonly involve the liver, lungs, and peritoneum. The case presented above was found to have extensive 1-5 mm metastases along the serosa of the jejunum during surgery. The lesions were undetectable by CT. Patients with metastatic disease are treated with Gleevec.

1. Levy AD, Remotti HE, Thompson WM, et al. Gastrointestinal stromal tumors: radiologic features with pathologic correlation. Radiographics. 2003:283-304, 456.
2. King DM. The radiology of gastrointestinal stromal tumours (GIST). Cancer Imaging. 2005;5:150-156.
3. Burkill GJ et al. Malignant gastrointestinal stromal tumor: distribution, imaging features, and pattern of metastatic spread. Radiology. 2003:226:527-532.