Gastrointestinal stromal tumour: spiral computed tomography features and pathologic correlation

Our purpose was to define the diagnostic accuracy of helical computed tomography (CT) in the identification, characterisation and evaluation of extension of gastrointestinal stromal tumours (GIST) through correlation with some pathological findings.

Between August 2000 and September 2004, we conducted a retrospective study of the abdominal CT of 15 patients with histological diagnosis of GIST - that is, the immunopositivity for c-kit (CD117) - on a surgical specimen of the primary disease. We used a helical CT single-slice (Toshiba, Asteion; rotation time 0.75 s) in ten cases and helical CT multislice (Toshiba, Aquilion; 4 slices/rotation; rotation time 0.5 s) in five cases. In all cases, we used an organ-iodate nonionic contrast agent intravenously at a concentration of 350-400 mgI/ml. All cases studied the entire abdomen. Site, morphology and tumour size (smaller than 5 cm, 5-10 cm and larger than 10 cm) were considered parameters for tumour identification. Size, partial or total extraluminal tumour growth, homogeneous or inhomogeneous lesion enhancement and the eventual presence of calcifications were assumed to be criteria for characterisation of a GIST. Hepatic, peritoneal and/or lymph node metastases were considered parameters of intermediate or high malignancy. We correlated the results with some pathological features derived from the analysis of surgical tissue: site, morphology and tumour size, tissue components and risk of malignancy of GIST (on the basis of the 2002 Fletcher classification).

We demonstrated one substantial concordance between radiological and pathological valuation of site, morphology, tumour size and absence of intralesional calcifications of GIST. Nine of ten GIST smaller than 5 cm, the two 5-10 cm and the three larger than 10 cm presented extraluminal growth. Enhancement was inhomogeneous in five of ten lesions smaller than 5 cm and in all cases larger than 5 cm. At pathological analysis, in all cases of inhomogeneous enhancement, solid, hemorrhagic, necrotic and cystic areas were found. Of seven tumours of intermediate malignancy, six were smaller than 5 cm and only one larger than 10 cm; the two 5-10 cm were of high malignancy and all tumours superior of 10 cm were at intermediate or high malignancy. Of the two cases with metastases, one was of intermediate and one of high malignancy. In the other cases of intermediate or high malignancy, metastases were absent.

The immunopositivity for c-kit is requisite for definitive diagnosis of GIST, but imaging, and particularly helical CT, has a primary role. In this study, CT is was reliable for tumour identification. All tumours larger than 5 cm presented extraluminal growth, inhomogeneous enhancement, absence of calcifications and lymph node metastases. Furthermore, the tumour larger than 5 cm showed extraluminal growth and inhomogeneous enhancement. Tumour size established with CT was not sufficient to determine the degree of malignancy. Metastases at the time of diagnosis were indicative of intermediate or high malignancy, but the absence of metastases did not allow classification of GIST in the group of low and very low risk of malignancy.