[Imaging of gastrointestinal stromal tumor (GIST): relation between CT findings and grade of malignancy].

Purpose: To report the relation between CT findings and the grade of malignancy in gastrointestinal stromal tumor (GIST), especially the uncommitted type of GIST.
Materials and Methods: A total of 14 patients with histologically proven GIST (uncommitted type) underwent CT. Tumors were divided into three grades. HISTOLOGICALLY: Benign (mitotic index [MI] < 2/10 high-power fields [HPF]), borderline (2/10 HPF < or = MI < or = 5/10 HPF), and malignant (5/10 HPF < MI). We evaluated tumor size, cystic component, margin, and early enhancement.
Results: All benign tumors were smaller than 5 cm, and most malignant tumors reached 5 cm. The size of borderline tumors was between the sizes of benign and malignant tumors. No benign tumors had cystic components, whereas all borderline and malignant tumors except for one case had cystic components. Only two huge malignant tumors had unclear margins. The relation between early enhancement and the grade of malignancy showed no tendency, but all duodenal tumors showed marked early enhancement irrespective of grade.
Conclusion: The grade of malignancy of GIST (uncommitted type) and size, presence of cystic components, and margin were highly correlated. That is, 1) tumors smaller than 5 cm with no cystic components can be diagnosed as benign, whereas 2) tumors that have cystic components are borderline or malignant. 3) Tumors that have cystic components and unclear margin can be diagnosed as actively malignant.