Diagnostic accuracy of high-resolution MRI as a method to predict potentially safe endoscopic and surgical planes in patients with early rectal cancer

Introduction Early rectal cancer (ERC) assessment should include prediction of the potential excision plane to safely remove lesions with clear deep margins and feasibility of organ preservation. Method MRI accuracy for differentiating ≤T1sm2 (partially preserved submucosa) or ≤T2 (partially preserved muscularis) versus >T2 tumours was compared with the gold standard of pT stage T1sm1/2 versus ≤pT2 versus >pT2. N stage was also compared. The MRI protocol employed a standard surface phased array coil with a high resolution (0.6×0.6×3 mm resolution). The staging data were analysed from a prospectively recorded database of all ERC (≤mrT3b) treated by primary surgery. Results Of 65 <mrT3b tumours, 45 were ≤pT2 and 14 were ≤pT1sm2. MRI accuracy for ≤T1sm2 was 89% (95% CI 63% to 87%), positive predictive value (PPV) 77% and negative predictive value (NPV) 92%, and for ≤T2 89% (95% CI 79% to 95%), PPV 93% and NPV 81%. Interobserver agreement between two experienced radiologists was >0.7 suggesting good agreement. 44 out of 65 patients underwent radical surgery and 22 out of 44 were ≤mrT2. MRI accuracy to predict lymph node status was 84% (95% CI 70% to 92%), PPV 71% and NPV 90%. Among the 21 out of 65 (32%) patients undergoing local excision or TEM, 20 out of 21 were staged as MR≤T2 and confirmed as such by pathology. On follow-up, none had relapse. If the decision had been made to offer local excision on MRI TN staging rather than clinical assessment, a significant increase in organ preservation surgery from 32% to 60% would have been observed (difference 23%, 95% CI 9% to 35%). Conclusions MRI is a useful tool for multidisciplinary teams (MDTs) wishing to optimise treatment options for ERC; these study findings will be validated in a prospective multicentre trial.