Doctors may need to use both MRI and rectal endoscopic sonography to do an accurate job of identifying intestinal endometriosis that requires rectal recession, or removal of part of the rectum. The study was published in the Journal of Minimally Invasive Gynecology. The title was "Magnetic Resonance Imaging Compared With Rectal Endoscopic Sonography for the Prediction of Infiltration Depth in Colorectal Endometriosis" Researchers said both magnetic resonance imaging and RES may be necessary for a proper diagnosis of endometriosis, and an accurate determination of its depth. Endometriosis involves tissue that should be growing inside the uterus growing outside it instead. Intestinal, or colorectal, endometriosis accounts for between 5-12 percent of endometriosis cases. Doctors define it as endometriosis that affects muscle surrounding the bowel. MRI and RES are often used to identify upper digestive lesions and the depth of colorectal lesions. Deep lesions may require surgery to remove part of the rectum. In less severe cases, doctors can shave off rectal tissue or cut out small parts of it. Researchers decided to compare MRI and RES's ability to predict the depth of colorectal endometriosis by evaluating patients who had had laparoscopic rectal resection. Laparoscopy is surgery with a thin, lighted tube inserted through an incision in the abdomen. The study covered 40 patients treated between 2012 and 2015. Doctors used either MRI or RES to try to determine the extent of their colorectal endometriosis. Researchers compared the MRI and RES results with the surgery results. MRI accurately predicted the depth of lesions in 20 cases. RES accurately predicted the depth in 23 cases. RES was less accurate at forecasting lesion depth than MRI, however. In fact, in three cases it overestimated depth, resulting in patients having unnecessary surgery. RES was more accurate on another measure, however: bowel invasion. RES flagged bowel invasion in 15 cases that MRI failed to flag. Doctors confirmed bowel invasion in 12 of the 15 cases, suggesting that RES is more accurate on this measurement. The overall results indicated that MRI is valuable for detecting intestinal endometriosis, but is less accurate than RES in detecting bowel invasion. When MRI detects bowel invasion, RES may be unnecessary, researchers said. But when MRI fails to detect intestinal lesions, RES should be used to confirm the diagnosis, they said. Such an approach will ensure that patients who do not need surgery will not undergo it, researchers said. Because the study covered a small number of patients, larger randomized trials are necessary to validate the findings, the team concluded.