Megarectum after surgery for anorectal malformations

Purpose: Megarectum complicating surgery for anorectal malformation (ARM) has implications for long-term continence. Factors influencing continence and defecation include intact rectal reservoir, innervation/proprioception of the anorectal muscle complex, functioning anorectal inhibitory reflex (AIR), and intact perception at the anal margin. We studied outcomes after surgery for ARM with emphasis on megarectum; particularly as to whether altered rectal proprioception from anatomic sacrococcygeal anomalies affect incidence. We also assessed whether an abnormal AIR could trigger passive rectal dilatation without mechanical obstruction. Methods: Eighty six infants (53 male) with ARM over 20 years were included. Demographics, surgical history, pathology, defecation patterns, imaging, manometry, and morbidity were analyzed. Incidence of sacrococcygeal malformations in children with and without megarectum was compared using Fisher exact test. Manometry results were evaluated for integrity of AIR and correlated to megarectum occurrence. Results: There were 23 high/intermediate and 63 low ARMs. Fourteen (16%) developed a megarectum: 6 of 23 in high and 8 of 63 in low anomalies (P = .33). Twelve patients underwent megarectum resection at a median of 2.6 years (7 months to 10 years); 2 received bowel management protocols. Fifty-seven percent (8/14) of children with and 7% (5/72) without megarectum had sacrovertebral anomalies (P = .0001). Patients with preoperative manometry (n = 5) demonstrated an intact AIR. Colonic manometry demonstrated hyperactive colons (n = 2). Constipation was the predominant preoperative symptom; 3 patients suffered from incontinence after resection. All the specimens showed normal innervation and thickened muscularis on pathology. Conclusions: Sacral anomalies, which are more prevalent in children who developed megarectum, may result in abnormal rectal proprioception contributing to this pathology. Innervation anomalies may coexist, although preoperative manometries showed normal AIRs. Rectal dysmotility may lead to stool retention with subsequent dilatation, and patients who underwent colonic manometry had diffuse colonic hypermotility. Further physiologic and cellular studies are needed to elucidate the causes of this significant complication after surgical ARM repair in the absence of obstruction.