© Pol J Radiol, 2011; 76(3): 38-48 Werewka-Maczuga A et al – Characteristics of computed tomography… Figure 1. Axial CT scans of the abdomen. Two cases of typical, intramural GISTs in their most frequent location in the stomach. Figure 2. Axial CT scans of the abdomen. Two cases of exophytic GISTs in the stomach. Figure 3. Axial CT scans of the abdomen and reconstruction of the study in the frontal plain. Two cases of endophytic GISTs in the stomach. On the left, there is a large ulceration in the tumor. Due to a relatively common exophytic growth of the tumor, the lesion may be impossible to detect endoscopically or may cause only slight modeling of the wall from the outside in the involved part of the GI tract. Standard endoscopic examinations are not helpful in the diagnostics of the small intestine either. Another method frequently used for diagnosing GIST tumors is the ultrasound examination due to its high avail- ability and commonness. Location of lesions inside the wall of the gastrointestinal tract significantly reduces the pos- sibility of their detection in ultrasound scans. In case of lesions that are visible in ultrasound, one may come across great difficulties in regard to identifying the point of ori- gin of the primary lesion and defining its type. Reports of ultrasound examinations, in which primary GISTs were found, are rarely correct in terms of the diagnosis of the tumor originating from the gastrointestinal wall. More often, diagnoses of pancreatic tumors and cysts, tumors of the liver, ovaries, or mesentery, and lymphomas are encountered, as well as abscesses between intestinal loops, intestinal inflammation or even an enlarged spleen. In the rare cases of retroperitoneal primary lesions, the diagnoses of renal and adrenal tumors predominate. The role of CT usually comes down to staging and deter- mining whether the lesions found through other diagnos- tic modalities are suitable for excision, as well as postop- erative control and monitoring of chemotherapy. In CT, asymptomatic primary tumors are often incidentally found during studies performed for other reasons. In CT diagnostics of GISTs one may encounter, although less often, similar difficulties in defining the character and point of origin of lesions as in ultrasound examina- tions. The following tumor characteristics influence these problems: • connection with the gastrointestinal wall, often difficult to visualize due to poor filling of the stomach and intes- tines with fluid or contrast medium, 39