Constipation and fecal incontinence are the frequent problems in the long-term period faced by ARM after surgical correction, which negatively affect the quality of life. Recent systematic reviews indicated that the true fecal incontinence was reduced to 12.4%-25% of patients, which may be related to the sphincter muscle complex well preserved or reconstructed through laparoscopic-assisted or posterior sagittal anorectoplasty [4, 17]. However, postoperative chronic constipation has been reported in more than half of patients with ARM who probably require lifelong treatment with laxatives [4, 17], and was observed in 35.4% of patients in our cohort. Given its negative impact on physical and psychological health across all developmental stages, constipation remains a significant concern for patients with ARM [18, 19].
Our results suggest that sacral agenesis (OR = 4.26, P = 0.002) and a shorter distal resection length (OR = 0.68, P = 0.007) are the independent factors for constipation. In terms of the sacral agenesis, the ARM with sacral agenesis may have higher risk of constipation associated with the effects on the extrinsic innervation originating from the sacrum(S2-S4)[20].
Most remarkably, there was a clear relationship between longer distal resection length (DRL) and lower constipation rate. It is reported that the postoperative constipation depends not only on the type of malformation and the condition of the pelvic floor musculature, but also on the histology of the blind pouch. Previous studies have reported that histopathological examination in the last 2-3cm of the rectal pouch showed large bundles of connective tissue in the muscularis propria and presented enteric nervous system abnormalities, related to the intestinal dysmotility and distal obstruction[8–10]. However, whether to resect the distal pouch remains controversial with several problems. First, there is a dearth of data, with only a few published studies focusing on bowel function improved after distal pouch resection. Furthermore, the incidence of soiling could be decreased by the preservation of the rectal pouch. Because the rectal pouch could be an equilibrium between the propagating forces of propulsive waves from the normal colon down to the distal rectum [5, 21, 22]. Finally, the colonic dysmotility in ARM with constipation may be associated with delayed maturation of enteric neurons[23]. The study from Borg et al. found that the constipation rate could drop from 64–25% at the age of 15 through the bowel management with no need to receive the resection of the rectosigmoid[12]. Despite this, the long-term bowel management could cause various psychological problems in these patients with ARM. A study by Amae et al. found a significant correlation between depression and constipation among patients with ARM aged 12–16 years, which is attributed to the frequent use of bowel management [24].
The present study evaluated the outcomes for resected group and control group after PSM. Of note, the incidence of the constipation in the resected group was significantly lower than that in control group (46.7% vs. 71.1%, P = 0.050). In contrast, the incidence of postoperative complications (20.0% vs. 15.7% P = 0.581) and constant soiling (11.1% vs. 15.7%, P = 0.979) was similar between the two groups in the matched cohort, and the constant soling rate was consistent with previous reports without distal resection(11.6–25%)[4, 25]. Thus, the resection of the rectal pouch can reduce the incidence of constipation without increment of soiling. A possible cause may be the intestinal motility and the capacity to absorb water impaired in the distal pouch of ARM due to the meconium accumulation before birth. Moreover, 70% of the children at 6 years after surgery did not require laxatives treatment in the resected group, potentially contributing to a higher quality of life. The early intervention of distal obstruction caused by neuromuscular abnormality may contribute to the defecation reflex reconstruction, preventing the vicious cycle of neuromuscular destruction and megasigmoid after anorectoplasty. In addition to the abnormality of the enteric neurons, the fibrosis of the rectal pouch at the last 3 cm is another concern. The intestinal fibrosis can also affect intestinal contraction and peristalsis, subsequently leading to the constipation[26].
The latest study confirmed the presence of intestinal fibrosis phenotypes in the transitional and ganglionic segments of patients with Hirschsprung's disease by single-cell transcriptomics [27]. And the postoperative obstruction and dysmotility is regarded as the incomplete resection of the transition zone[28]. Therefore, it is speculated that the fibrosis of the transitional segments may be also attributed to postoperative constipation in Hirschsprung’s disease. However, the fibrosis of the rectal pouch in ARM is also common and easily overlooked. The subepithelial fibrosis was found in 71% of the cases from the research of Pandey et al and in 90% from Gangopadhyay et al[9, 29]. In accordance with the report form Lombardi et al, our previous research also found the fibrosis of muscularis propria of the distal rectum from 52 patients with ARM[7, 8, 10]. Currently, we furthermore constructed longitudinal histopathological examination of the rectal pouch to show variation in the degree of fibrosis (Fig. 1). The Masson trichrome staining indicated that the presence of the fibrosis and the degree of fibrosis decreased from the distal to the proximal segment, especially within 3cm from the end of the rectal pouch. This discovery provides an explanation for the observed rigidity and dilation of the distal pouch during surgery, as well as the higher rate of constipation in the control group, which had fibrotic residue in the distal rectum.
However, some limitations worth noting. This study was based on a retrospective cohort in which pathological sections which may only be a portion of the rectal pouch were retrieved from the pathology archives, and thus we cannot ascertain whether the pathological characteristics were derived from proximal to distal pouch. Thus, further validation is deserved to determine the distribution of fibrosis in different types of ARMs or along the longitudinal axis of the rectum to help surgeons perform more precise resection. Furthermore, this study involves single-center cohort and no patients with no distal resection, and the results should be interpreted with some caution.