14 - Gastrointestinal Stromal Tumors: Positron Emission Tomography and Contrast-Enhanced Helical Computed Tomography

Abstract

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal neoplasias of the gastrointestinal (GI) tract. Mesenchymal tumors of the GI tract represent 1% of the primary GI tumors, but most of the mesenchymal tumors fall into the GIST category. Approximately 70% of the tumors have their origin in the stomach, and 20% originate from the small intestine but can also occur in other parts of the gastrointestinal tract and are occasionally found in the omentum, mesentery, and peritoneum. GISTs have a wide clinical spectrum from benign incidentally found lesions to large tumors. Positron emission tomography (PET) using 18F-fluorodeoxyglucose (FDG) has been used successfully for staging and follow-up examinations in cancer patients. This tomography using FDG provides physiologic information that enables cancer to be diagnosed on the basis of altered tissue metabolism. FDG-PET is more accurate in staging and re-staging FDG-avid cancer than ceCT examinations. FDG-PET does not depict all GIST lesions compared to ceCT scans. However, there is a significant correlation between the FDG uptake and the mitotic index of the GIST cells. Regarding the prognostic relevance of the mitotic index in GIST, FDG-PET can provide a significant impact on the further outcome of GIST patients. Morphological imaging with contrast-enhanced computed tomography (ceCT) is widely used to localize GIST as well as in determining the size and possibly revealing the presence of secondary localizations. Furthermore, ceCT is routinely used to monitor tumor response in patients with GIST.