Background. Rectal Magnetic Resonance Imaging (MRI) is a key test in advanced rectal cancer and in the preoperative staging of a lesion suitable for transanal endoscopic surgery (TES). MRI is not operator-dependent, but its results when determining anatomical landmarks are variable.
Method. Observational study of inter-observer concordance regarding four diagnostic tests used to establish the anatomical characteristics of rectal lesions: colonoscopy, rectal ultrasound (EUS), rectal MRI, and intraoperative rigid rectoscopy (IRR) in patients scheduled for transanal endoscopic surgery (TES) with curative intent. This inter-observational study assessed the concordance between four expert radiologists regarding the topographic evaluation by means of rectal MRI of lesions under consideration for TES.
Results. Fifty-five consecutive rectal tumors were studied. For most of the items, the correlation between IRR and colonoscopy or EUS was generally very good (intraclass correlation coefficient -ICC-)>0.75), although the correlation between MRI and IRR in relation to size by quadrants (ICC=0.092) and location by quadrants (ICC=0.292) was weak. The ICC for the other items obtained excellent correlations: Kappa index >0.80 for all items except for the distance from the peritoneal reflection to the anal verge, where it was merely good (IK=0.606).
Conclusions. The anatomical description of rectal lesions that are candidates for TES provided by means of IRR, EUS, colonoscopy and MRI is reliable. The MRI is less reliable, but in the hands of expert radiologists, the anatomical study of rectal lesions is accurate and reproducible.