Role of CT scan in differentiating the type of colorectal cancer

Most colorectal cancers are classical adenocarcinomas (AC), and less frequent subtypes include mucinous adenocarcinomas (MAC) and signet-ring cell carcinomas (SC). The purpose of this study was to evaluate the computed tomography (CT) findings that can help to differentiate MAC and SC from AC.

CT scans of 168 patients with pathologically proven MAC and 67 patients with pathologically proven SC were analyzed, and 220 patients with classical AC were also included as a control group. CT findings of the three groups were compared and contrasted in terms of the bowel involvement patterns, contrast enhancement patterns, and presence or absence of bowel obstruction, intratumoral calcification, pericolic fat infiltration, and local tumor extension to adjacent organs. Statistical analyses were made by using the one-way analysis of variance, least significant difference test, and Pearson's chi-square test.

Compared with classical AC, the MAC showed more severe (6.29±2.69 cm vs 4.57±1.74 cm, P<0.001) and higher percentage of occurrence of eccentric bowel-wall thickening (37.2% vs 11.5%, P<0.001). Heterogeneous contrast enhancement was most common in MAC (P<0.01), and MAC showed more areas with hypoattenuation (P<0.001). The presence of intratumoral calcification was most frequent in MAC (17.9% vs 2% vs 6.8%) (P<0.001); the SC also were more severe (5.75±2.28 cm vs 4.57±1.74 cm. P=0.001) than AC, but SC tend to show more cases of concentric even bowel-wall thickening (67.2%); homogeneous contrast enhancement was most common in SC (P<0.01), and it showed a target appearance. The presence of peritoneal seeding was most frequent in SC (35.8% vs 8% vs 2.7%, P<0.001), while the presence of regional lymph node metastasis (P=0.190) and direct invasion of adjacent organs or metastasis (P=0.323) were not significantly different among them.

Some radiological features by CT can be used to classify different colon tumor types.