Objective To investigate CT colonography (CTC) performance for detecting and characterising synchronous lesions proximal to a stenosing colorectal cancer and to suggest patient management strategies according to the CTC findings.

Methods 411 consecutive patients underwent CTC for proximal colonic evaluation after failed colonoscopy past a newly diagnosed stenosing colorectal cancer. Pathological examination of colectomy specimen and/or postsurgical colonoscopy with pathological confirmation of the proximal synchronous lesions to serve as reference standards existed in 284 patients. Per-patient and per-lesion diagnostic performance measures of CTC for diagnosing proximal synchronous lesions ≥6 mm analysed by histopathological categories were obtained for the 284 patients. Per-lesion sensitivity and positive predictive value (PPV) of various CTC lesion size criteria and lesion size combined with other CTC findings for diagnosing cancer in the proximal colon were determined.

Results Both per-patient and per-lesion CTC detection sensitivities for proximal synchronous cancers were 100% (6/6 patients and 8/8 lesions; 95% CI 64.3% to 100% and 70.7% to 100%, respectively) with the corresponding per-patient negative predictive value (NPV) of a negative CTC of 100% (194/194 patients; 95% CI 98.3% to 100%). Per-patient NPV of a negative CTC for advanced neoplasia (ie, advanced adenomas and colorectal cancers) was 97.4% (189/194 patients; 95% CI 93.9% to 99.1%). A lesion size ≥15 mm on CTC as the criterion to specifically diagnose proximal cancer yielded 87.5% (7/8 lesions; 95% CI 50.8% to 99.9%) per-lesion sensitivity, rendering one 8-mm submucosal cancer mischaracterised as a non-cancerous lesion, and 70% (7/10 lesions; 95% CI 39.2% to 89.7%) per-lesion PPV. Additional CTC findings did not improve the sensitivity.

Conclusion CTC is highly sensitive in detecting synchronous cancers proximal to a stenosing colorectal cancer. CTC has limited capability in differentiating advanced adenomas from colorectal cancer and this compromises the PPV of CTC for the presence of proximal cancer.