To the best of our knowledge, this is the first study to investigate the effect of rectal ESD on defecation function. Our findings suggest that patients who undergo extensive resections reaching the dentate line (Group A) are more likely to experience changes in anorectal function. In Group A, patients with mucosal defects encompassing more than two-thirds (≥ 0.66) of the rectal circumference showed shortened HPZ and decreased maximum rectal pressure during straining. Additionally, in 1 out of 3 patients, the evacuation ability of the barium paste decreased during defecography. Conversely, patients with mucosal defects that did not extend to the dentate line (Group B) experienced minimal changes in the rectal sensation, with intact HPZ and evacuation ability functions.
In general, HPZ, MRP and MSP are functional indicators of the internal and external anal sphincter on anorectal manometry, respectively [14]. Patients with fecal incontinence are more prone to unconscious leaks due to their shortened HPZ and lower MRP compared with those with normal continence [15]. In this study, an HPZ shortening of 4.5 cm was found in one patient with barium paste incontinence. In comparison, the 10 other cases with an average HPZ shortening of 1.0 cm displayed minimal to no incontinence. As such, barium paste incontinence can be associated with significantly shortened HPZ post-ESD. On the contrary, MSP, which reflects the conscious contraction of the external anal sphincter to the maximum extent [15], remained largely unchanged post-ESD. This suggests that rectal resection had minimal impact on voluntary stool control.
Changes in anal and rectal pressure during straining reflect defecation efficiency [16]. Thus, for patient No. 11, who displayed compromised defecation function, a significant decrease of maximum intrarectal pressure during straining (-8.8 mmHg) post-ESD indicates reduced evacuation power due to extensive mucosal defects affecting intrarectal pressure.
Although sphincter-preserving surgery is widely performed for rectal and anal canal tumors, it has been linked with post-operative alterations in defecation function, affecting 60-80% of cases that range from mild to severe symptoms [17]. Furthermore, 50% of cases have even reported the persistence of abnormal post-operative defecation function for over 10 years, leading to a long-term decline in QOL [18-20]. One study also showed that surgical resection impairs internal anal sphincter function, evidenced by shortened HPZ and decreased MRP [21]. Older adults are particularly susceptible to fecal incontinence and constipation due to surgical changes on top of age-related changes in anal sphincter functions [22-25].
In contrast, ESD has significant advantages due to its minimally invasive nature and improved post-operative QOL. In Japan, multiple institutions have examined the short- and long-term outcomes of colorectal ESD from 2007 to 2010. These studies have reported an en-bloc resection rate of 94.5%, an intraoperative perforation rate of 1.6%, a post-operative bleeding rate of 2.2%, and a 5-year long-term prognosis of 94% for curative resections [26-29]. Collectively, these findings support ESD as an excellent and safe curative treatment for early-stage cancer. However, extensive ESD resections reaching the dentate line may be necessary in certain cases. In such situations, ESD may cause pain due to the manipulation of epithelial sensory nerves adjacent to the dentate line [30], and extensive circumferential resections (> 90%) and anal canal involvement were identified as significant risk factors for post-ESD stenosis [28, 31-34]. A previous study reported 17.6% of anorectal canal cases who underwent resections exceeding 75% of the lumen reported the development of anal stenoses, with patients experiencing difficulty defecating and narrowed stool caliber [35]. These findings indicate that both surgery and ESD can negatively affect defecation function in the anorectal region.
Notably, two patients in our study reported an increase of ≥2 points on post-ESD CSS evaluation, although normal barium paste excretion and no real-world defecation problems were observed. This is likely because they did not experience severe constipation pre-ESD, and while the dentate line may have been resected, neither of them exceeded 90% of the circumference. Additionally, most patients with mucosal defects involving the dentate line have relatively small lesions, minimizing the likelihood of post-operative anorectal dysfunction.
Notably, one female patient who underwent extensive resection reaching the dentate line experienced resolution of a pre-existing rectocele post-ESD. Rectoceles, defined as the prolapse of the rectovaginal septum toward the vagina due to chronic stress from pregnancy, childbirth, or constipation [36], have also been implicated in the sensation of incomplete or difficulty in defecation [37]. While this patient showed no symptoms of constipation pre-ESD and showed no changes in barium paste excretion post-ESD, the contributory effect of her rectocele cannot be ruled out. Surgery is an option for the treatment of severe rectoceles that are refractory to laxatives; however, our findings suggest the potential utility of endoscopic approaches for rectocele management.
This study holds significance as the first to evaluate the effect of rectal ESD on defecation function using anorectal manometry and defecography. We demonstrated that extensive resections reaching the dentate line may alter defecation function. Therefore, evaluating anorectal function via manometry and defecography can lead to establishing new treatment methods.
Despite the valuable insights offered in this study, certain limitations should be acknowledged. First, this was a single-institution pilot study with a small sample size, which limits the generalizability of our findings. Second, this study lacked data on long-term changes in defecation function. Finally, the lesions in Group B were smaller than in Group A. As such, we could not rule out the possibility that defecation function changes in Group A were due to the size of the mucosal defect. Future studies with larger cohorts and well-matched lesion sizes are necessary to draw definitive conclusions.
In conclusion, our study showed that rectal ESD with extensive ranges, particularly those that reach the dentate line, may alter the morphology and function of the anorectal canal. Nevertheless, patients are unlikely to experience significant real-world defecation difficulties following the procedure.