Colorectal neoplasms: Role of intravenous contrast-enhanced CT colonography

PURPOSE: To evaluate whether computed tomographic (CT) colonography with intravenously administered contrast material can help predict malignant differentiation of colorectal neoplasms (≥10 mm in diameter). MATERIALS AND METHODS: Enhancement of 29 consecutive colorectal neoplasms on pre- and postcontrast CT colonographic images was retrospectively measured. The neoplasms were subsequently resected. Enhancement was calculated by subtraction of attenuation values (in Hounsfield units) obtained with precontrast and postcontrast 45-second-delay prone CT colonographic sequences. The neoplasms were graded as follows: grade 1, adenoma; grade 2, adenoma with high-grade dysplasia; grade 3, well-differentiated adenocarcinoma; grade 4, moderately differentiated adenocarcinoma; and grade 5, poorly differentiated adenocarcinoma. Correlation among size, histologic grade, and degree of enhancement was made with Pearson and Spearman coefficients. The ability of the degree of enhancement to help predict adenocarcinoma (histologic grade, ≥3) was calculated. RESULTS: Histologic-CT colonographic correlation was performed in 29 neoplasms (mean diameter, 27.9 mm; range, 10-65 mm). There was no correlation between size and degree of enhancement, size and histologic grade (R = -0.17, P = .33), or histologic grade and degree of enhancement (R = 0.23, P = .23). However, increasing enhancement was noted between grades 2 and 5. When an enhancement threshold of 40 HU was used for the diagnosis of adenocarcinoma (grades 3-5), sensitivity was 92%, specificity was 20%, positive predictive value was 50%, and negative predictive value was 75%. CONCLUSION: The degree of contrast enhancement on a 45-second-delay CT colonographic image does not correlate with size or degree of histologic differentiation, although increasing enhancement with lesser degrees of differentiation was noted.