Posterior mesorectal thickness as a predictor of increased operative time in rectal cancer surgery: a retrospective cohort study

Background In rectal cancer surgery, larger mesorectal fat area has been shown to correlate with increased intraoperative difficulty. Prior studies were mostly in Asian populations with average body mass indices (BMIs) less than 25 kg/m 2 . This study aimed to define the relationship between radiological variables on pelvic magnetic resonance imaging (MRI) and intraoperative difficulty in a North American population. Methods This is a single-center retrospective cohort study analyzing all patients who underwent low anterior resection (LAR) or transanal total mesorectal excision (TaTME) for stage I–III rectal adenocarcinoma from January 2015 until December 2019. Eleven pelvic magnetic resonance imaging measures were defined a priori according to previous literature and measured in each of the included patients. Operative time in minutes and intraoperative blood loss in milliliters were utilized as the primary indicators of intraoperative difficulty. Results Eighty-three patients (39.8% female, mean age: 62.4 ± 11.6 years) met inclusion criteria. The mean BMI of included patients was 29.4 ± 6.2 kg/m 2 . Mean operative times were 227.2 ± 65.1 min and 340.6 ± 78.7 min for LARs and TaTMEs, respectively. On multivariable analysis including patient, tumor, and MRI factors, increasing posterior mesorectal thickness was significantly associated with increased operative time ( p = 0.04). Every 1 cm increase in posterior mesorectal thickness correlated with a 26 min and 6 s increase in operative time. None of the MRI measurements correlated strongly with BMI. Conclusion As the number of obese rectal cancer patients continues to expand, strategies aimed at optimizing their surgical management are paramount. While increasing BMI is an important preoperative risk factor, the present study identifies posterior mesorectal thickness on MRI as a reliable and easily measurable parameter to help predict operative difficulty. Ultimately, this may in turn serve as an indicator of which patients would benefit most from pre-operative resources aimed at optimizing operative conditions and postoperative recovery.