Post-radiation levator ani atrophy is associated with worse Low Anterior Resection Syndrome score after nonoperative management for locally advanced rectal cancer: a potential MRI biomarker

Background: Nonoperative management is increasingly offered to patients who achieve a complete clinical response to neoadjuvant therapy for rectal cancer. However, long-term bowel dysfunction and fecal incontinence can occur, potentially due in part to post-radiation fibrosis and atrophy of the pelvic floor muscles. In this pilot study, we investigated post-radiation changes in the levator ani muscles and their association with long-term patient-reported bowel dysfunction and incontinence scores. Methods: Fifteen patients with rectal cancer treated with definitive chemoradiation followed by non-operative management were included. 2D and volumetric measurements of the levator ani were made on pre-treatment and 1-year post-radiation MRI. The changes in levator ani width and volume were correlated with the Low Anterior Resection Syndrome (LARS) and Fecal Incontinence Quality of Life (FiQOL) scores at least 1-year post treatment. Results: The 2D and volumetric measurements of the levator ani decreased between pre-treatment and 1-year post-radiation. (-21.0% and -21.7%, respectively; both P