Digestive disorders

III./3.3.: Computed tomography – CT

CT is the basic investigation method in the regard of GIST diagnostics, staging and therapy monitoring. The contour of gastric wall tumor, which is usually already large at detection, is smooth, its density is mixed, and central hypodensity referring to necrosis is a common finding. Small tumors are rather homogeneous, hypodense and well circumscribed. Contrast enhancement is homogeneous and high. However, these characteristics are not enough to diagnose GIST in case of a – otherwise unknown – small tumor. Patchy enhancement is characteristic for the larger tumors, since necrotic areas do not enhance. Consequent to the necrosis, fistula formation is common between the tumor tissue and the gastrointestinal lumen. As a regressive lesion, calcification may also occur in GIST, which can be imaged by CT unequivocally.

Tumor sizes and propagation can be detected on CT, and metastases can be easily identified. In case of GISTs – principally in ones of intestinal origin – mesenteric/omental propagation is common, especially in relapsus (surgical contamination?). In this case, hyperdense enhancing nodules can be observed in the mesenterium with hypodense center. The tumor mass can compass the mesenteric veins, leading to occlusion. Omental metastases/spread can occur as well. Ascites is rare and a little. Liver metastases are often small and enhance the contrast well in portal phase due to their hypervascular feature, and rapid wash-out is characteristic in venous phase (to detect them, two-, or three phasic investigation is necessary). Hypovascularised metastases may also occur.

Sometimes the origin of the tumor can not be identified due to its localisation: e.g. if located closely to the head of pancreas , or to the oesophagus proximally. Small bowel GISTs  may mimic lymphoma. Diagnosis is very difficult in these cases by imaging morphology.