Comparison between magnetic resonance imaging and rigid rectoscopy in the preoperative identification of intra- and extraperitoneal rectal cancer F. Paparo*, C. Puppo*, A. Montale†, L. Bacigalupo*, A. Pascariello‡, M. Clavarezza§, C. Binda†, G. A. Rollandi* and G. A. Binda‡ *Department of Radiology, E.O. Ospedali Galliera, Genoa, Italy, †School of Medicine, Genoa, Italy, ‡Department of General Surgery, E.O. Ospedali Galliera, Genoa, Italy and §Oncology Unit, E.O. Ospedali Galliera, Genoa, Italy Received 8 January 2014; accepted 17 May 2014; Accepted Article online 8 October 2013 Abstract Aim Accurate preoperative discrimination between extra- and intraperitoneal rectal cancer has important treatment implications. Our main objective was to compare the diagnostic performance of MRI with rigid rectoscopy (RRS) in assessing the location of rectal cancers above or below the peritoneal reflection (PR), using the findings obtained during abdominal surgery for treatment of the cancer as the reference standard. We also compared the accuracy of MRI and RRS in assessing the level of the lower border of the tumour from the anal verge. Method Patients with rectal carcinoma awaiting surgery underwent MRI and RRS. The MRI images were reviewed by two abdominal radiologists who determined the location of the inferior border of the tumour in rela- tion to the PR. Receiver–operating characteristics (ROC) curve analysis was performed to determine the diagnostic performance of RRS at different cut-off values. Results The sensitivity and specificity were 98.15% and 100%, respectively, for MRI, and 100% and 76.92%, respectively, for RRS at a cut-off value of < 10 cm. The mean level of the lower border of the tumour from the anal verge was 68 Æ 44.3 mm on RRS and 73.5 Æ 42.4 mm on MRI (P = 0.25), with a trend towards overestimation with MRI. Conclusion RRS is still the main means of assessing the level of a rectal tumour from the anal verge, but MRI has value in determining the level of the tumour in rela- tion to the PR, which cannot be seen on endoscopy. Keywords Rectal cancer, rectoscopy, MRI, perito- neum, surgery What does this paper add to the literature? To our knowledge, this is the first study focusing on the comparison between the diagnostic performance of MRI and rigid rectoscopy in assessing the location of rectal cancer with respect to the anal verge and perito- neal reflection. Introduction The discrimination between intra- and extraperitoneal rectal cancer has important treatment implications because the risk of local recurrence increases as the cancer moves distally towards the anal verge [1,2]. The antero- lateral wall of the upper third of the rectum is covered by peritoneum [3], and tumours above the peritoneal reflec- tion (PR) exhibit the same clinicopathological behaviour as colon cancer [4]. Chemotherapy is administered as standard adjuvant treatment for radically resected colon cancer with involved regional lymph nodes [5], whilst combined chemoradiation is commonly given preopera- tively for locally advanced extraperitoneal rectal cancer [6,7]. Anatomically, the upper limit of the rectum is the rectosigmoid junction, slightly below the sacral promon- tory [8]. Its lower limit is the point at which it becomes the mid-rectum. Here, the PR is considered a reliable anatomical landmark for distinguishing between the ex- traperitoneal rectum and the intraperitoneal rectum [9]. This point is usually referred to in the histopathological report of the resected specimen [2], but it would be very useful to know the level preoperatively in order to plan the management. This information may be obtained by MRI and rigid rectoscopy (RRS) [8]. The latter also Correspondence to: Francesco Paparo, MD, Department of Radiology, E.O. Ospedali Galliera, Mura della Cappuccine 14, 16128 Genoa, Italy. E-mails: francesco.paparo@galliera.it; francesco.paparo.ge@gmail.com Colorectal Disease ª 2014 The Association of Coloproctology of Great Britain and Ireland. 16, O379–O385 O379 Original article doi:10.1111/codi.12698