Comparison study between Magnetic Resonance Imaging (MRI) and rigid rectoscopy in assessing the extraperitoneal location of rectal cancers A. Pascariello(1), C. Puppo(2), A. Montale(1), F.Paparo(2), L. Bacigalupo(2), G.A. Rollandi(2), G.A. Binda(1) (1) General and Epatobiliary Surgery Department, EO Ospedali Galliera, Genoa, Italy (2) Radiology Department, EO Ospedali Galliera, Genoa, Italy BACKGROUND Figure 1. Surgical demonstration of the anterior peritoneal reflection. Figure 2. T2-weighted MRI sagittal (A) and axial (B) images in two different patients with extraperitoneal rectal cancer (arrowhead). Arrow indicates anterior peritoneal reflection. Discriminating between intra- and extraperitoneal rectal cancers has important treatment implications. Combination chemotherapy represents in fact the standard adjuvant treatment for radically resected colon cancer, at least in the presence of involved regional lymph nodes, and for intraperitoneal rectal cancer, while radiation, combined with FU-based chemotherapy, is routinely used for advanced extraperitoneal rectal tumours and preferentially administered before surgery [1]. In many studies, the definitions of extraperitoneal rectal cancer are somewhat arbitrary, according to the distance of the inferior edge of the tumor from the anal verge [2]. The anterior peritoneal reflection separates the intra and extraperitoneal portions of the rectum and is a well-defined anatomic landmark at laparotomy [3]. MRI can accurately demonstrate the pelvic anatomy, including the anterior peritoneal reflection [4,5]. PURPOSE Aim of this study was to compare the diagnostic accuracy of rigid rectoscopy with that of MRI in assessing the extra or intraperitoneal location of rectal cancers, using surgical exploration as reference standard (fig.1). A B METHODS Patients with surgically proven primary rectal adenocarcinoma were retrospectively identified performing a search in our single institution surgical database. All patients that underwent both pre-operative rigid rectoscopy and MRI were enrolled. Patients with a complete response to chemoradiation treatment were excluded. MRI studies were reviewed in consensus by two experienced abdominal radiologists, who had to define the intra- or extraperitoneal location of the inferior edge of tumors. The diagnostic accuracy of MRI was calculated. Three different cut-off measurements were used to define the diagnostic accuracy of rectoscopy: ≤10 cm, ≤12 cm and ≤16 cm. RESULTS Graphic 1. Correlation between the distance from the inferior edge of the tumor to anal verge measured with MRI and rigid rectoscopy Graphic 2. Bland-Altman plot shows a trend of overestimation of MRI over rigid rectoscopy in regard to the distance between inferior margin of the tumor and anal verge. MR TECHNIQUE All of the MRI examinations were performed with a 1.5T MRI scanner. No bowel preparation, endorectal filling or intravenous antispasmodic agents were used. Using a phased array pelvic coil, T2 weighted fast spin echo sequences with a slice thickness of 4.0 mm were performed in orthogonal planes. Images were also acquired in axial and coronal planes perpendicular and parallel to the long axis of the tumor. An additional axial DWI (diffusion-weighted) sequence was performed for aiding the observers in the visualization of the inferior edge of the tumor and nodal involvement. Arithmetic mean difference -5,5 mm (CI -6,7828 to -4,2475). Table 2. Diagnostic accuracy of MRI and rigid rectoscopy using different cut-off values Table 1. Characteristics of patients MRI Rectoscopy cut-off values ≤10 ≤12 ≤16 Sensitivity 92.45% 100% 100.00% Specificity 76.92% 53.85% 38.46% Disease prevalence 80.30% Positive Predictive Value 94.64% 89.83% 86.89% Negative Predictive Value 76.47% Number of enrolled patients (n= 66) Age 69.4 ± 9.6 Female Male 27 (41%) 39 (59%) Prevalence of extraperitoneal cancers 53/66 (80%) Prevalence of intraperitoneal cancers 13/66 (20%) CONCLUSIONS MRI and rigid rectoscopy show to have a good correlation in regard to the distance between the inferior edge of the tumor and the anal verge (mean difference of 5,5 mm) with a trend of overstimation with MRI (mean 5,5 mm) . MRI is an accurate imaging tool for determining the position of the inferior margin of tumors with respect to the anterior peritoneal reflection, and, consequently, the intra- or extraperitoneal location of rectal cancers. 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