Understanding and Tailored Treatment of Low Anterior Resection Syndrome

Low anterior resection syndrome (LARS) is a common long-term complication after colorectal cancer surgery. Up to 80% of patients experience symptoms such as urgency, frequent bowel movements, clustering, and fecal incontinence. These symptoms can severely affect quality of life, and the underlying causes are not fully understood. LARS appears to result from several interacting mechanisms, including sensory changes, altered motility, reduced reservoir function, sphincter dysfunction, and effects of chemotherapy or radiotherapy. Because different patients may have different dominant mechanisms, treatment responses vary widely. This observational study aims to investigate the physiological and imaging characteristics of LARS using advanced assessment methods. The goal is to better understand the mechanisms behind LARS, identify distinct patient subtypes, and support development of more targeted treatment strategies. The study will include 50 patients with minor or major LARS after rectal cancer surgery. Their results will be compared with four control groups: * patients who had rectal cancer surgery but did not develop LARS, * patients with fecal incontinence (before/after sacral nerve stimulation), * patients with urge fecal incontinence (before/after dorsal genital nerve stimulation), and * patients treated with organ-preserving chemoradiotherapy ("watch-and-wait"), whose rectum has not been surgically removed. All participants will attend a single study visit that includes advanced physiological measurements, Magnetic Resonance Imaging (MRI)-based assessments, and standardized questionnaires. These methods are not part of routine clinical care but are used to explore mechanisms such as motility, sensory function, sphincter activity, and rectal reservoir function. Patients with LARS will also be followed during their standard stepwise treatment pathway. They will complete questionnaires before and during each treatment step, which may include dietary advice, medication, pelvic floor training (biofeedback), and rectal emptying techniques such as mini-enemas or transanal irrigation. This follow-up will help determine how different physiological patterns relate to treatment response. The study is conducted in collaboration between Aarhus University Hospital and Aalborg University Hospital, with expert input from The Royal London Hospital (UK) and Motilis SA (Switzerland).