Long-term follow-up in patients with anorectal malformation: MRI findings in relation to bowel function

AIM OF THE STUDY: This study aims to evaluate the post-reconstruction pelvic anatomy on MRI in the long-term follow-up of patients with anorectal malformations (ARMs) and to explore associations between MRI findings and functional outcomes. METHODS: From January 2023 to June 2025, adolescents aged 12 to 18 with ARM underwent MRI and completed a functional outcome questionnaire. The position of the rectum and neoanus, pelvic floor muscle development, anorectal angle, rectal diameter, remnant of the original fistula (ROOF), fat interposition, perirectal fibrosis, and incidental findings were assessed. MRI findings were compared between simple and complex ARMs, and associations with functional outcomes were explored. MAIN RESULTS: Forty-seven patients underwent MRI (21 simple, 25 complex, and one unknown ARM type). MRI displayed a ROOF in 3/47 patients (6.4 %), a rectal diameter >50 mm in 4/47 (8.5 %), and previously unrecognized gynecological anomalies in 5/6 (83.3 %) cloacal malformation patients. Compared with simple ARMs, complex cases more frequently showed lateral rectal displacement at the puborectal muscle level (32 % vs 0 %, p = 0.005) and intermediate/poor puborectal muscle development (68 % vs 14.3 %, p < 0.001), and demonstrated a wider median anorectal angle (136° [IQR 118.5-150] vs 119° [IQR 104.5-140], p = 0.037). In simple ARM without tethered cord or sacrococcygeal anomalies, fat interposition was associated with difficulty withholding defecation (p = 0.027), and perirectal fibrosis with reduced urge sensation (p = 0.022). CONCLUSIONS: This study highlights the value of MRI during the long-term follow-up of patients with ARM, as it detects previously unrecognized anomalies, provides new leads for improving functional outcomes, and supports a well-informed transition to adult care with optimized functional outcomes.