Colorectal cancer is the third most prevalent malignancy worldwide, accounting for approximately 10.0% of total cancer cases (1). Its incidence is progressively leaning toward younger demographics, evident in the proportion of cases among individuals below 55 years of age in the United States, which increased from 11% in 1995 to 20% in 2019 (2). Young patients often exhibit a profound demand for postoperative dignity and defecation. Since the introduction of intersphincteric resection (ISR) by Heseker et al. in 1994 (3), ISR has emerged as the ultimate anal-preservation surgery for distal rectal cancer. Its surgical indications have expanded to include cases in which the lower edge of the tumor is <4 cm from the anal verge (4). However, up to the present time, involvement of the external anal sphincter (EAS) or levator ani (LA) remains a contraindication for ISR surgery (4). Additionally, owing to the frequent association of ultra-low rectal cancer (ULRC) with anal canal involvement, following the treatment guidelines recommended by the National Comprehensive Cancer Network entails performing abdominoperineal resection (APR) procedure (5). This results in an inability to preserve the anus, which is unacceptable for certain patients. They believed that losing the anus would compromise their dignity, and that having a stoma bag attached to the abdominal wall would disrupt their daily lives and exacerbate psychological distress. Their concerns included the potential for fecal odor leaking from the stoma bag and affecting others, the possibility of bag rupture if not changed promptly, and the fear of social isolation as others may distance themselves because of the presence of the stoma bag. Smith et al. (6) have also indicated that some patients undergoing stoma surgery suffer from significant physical and psychological distresses. Therefore, they would forgo treatment altogether rather than relinquish their anus. Thus, this study aimed to investigate whether in situ anal reconstruction could preserve the anus in patients with ULRC/anal canal cancer (ACC) while ensuring radical resection of the cancer.

Current research indicates that the functionality of pelvic floor muscles (PFMs) decisively controls the quality of defecation function (7–9). PFMs are mainly composed of the internal anal sphincter (IAS), EAS, and other together. Among these, the IAS is an involuntary muscle that adjusts closure and relaxation in response to rectal content, whereas the EAS and LA are voluntary muscles that can contract through self-aware control, thus resisting pressure within the rectum during defecation (10). The puborectalis muscle (PM) serves as the sensory center for the urge to defecate (11, 12). The two legs of the PM converge at the posterior aspect of the anorectal junction, forming a sling that exerts forward traction at the anorectal junction, thus creating an anorectal angle (10). The PM controls the anorectal angle. During contraction, the PM compresses the rectum from the side, causing it to move forward and upward, thereby narrowing the anorectal angle. This mechanism resembles that of a gate, which prevents fecal matter from descending into the anal canal (10). Morgan et al. (13) concluded that as long as the morphology of the PM is intact, some degree of defecation can still be preserved. The PM plays a pivotal role in defecation.

The present study confirms that the functional strength of the PM is directly proportional to its thickness (14). Hence, we assessed the functional strength of the PM by considering its thickness and, in conjunction with digital rectal examination (DRE), conducted a preliminary evaluation of PFM functionality. We propose that patients with ULRC/ACC with good PM function can maintain partial defecation after undergoing combined procedures of partial PFM resection with in situ anal reconstruction (PPFMR with ISAR). Here, we present three case reports.

The patient was placed in the lithotomy position under general anesthesia, and a pneumoperitoneum was established at 12–15 mmHg. Employing the conventional 5-port technique, a 10-mm incision was made 0.5 cm above the umbilicus to create the observation port for pneumoperitoneum. A 12-mm trocar was inserted within the right anterior superior iliac spine, and three 5-mm trocars were placed at the midpoint of the line connecting the right clavicle to the umbilicus, the umbilicus to the midpoint of the line connecting the left anterior superior iliac spine, and the symphysis pubis joint.

The inclusion criteria were as follows: PM thickness ≥ 6·5 mm for the left side and ≥4·9 mm for the right side and Oxford Modified Grading Scale ≥ grade 5; the patient strongly insisted on preserving the anus and refused stoma surgery, stating that they would rather forgo treatment altogether if preserving the anus was not viable; no pre-operative radiotherapy or chemotherapy was administered; and the ULRC/ACC invaded >1 cm below the dentate line with no distant metastasis. The baseline data of the three selected patients are shown in Table 1.

Petros et al. (15) contended that the integral pelvic floor is a closely interrelated entity and that its complete functionality is achieved through the mutual coordination of the PFMs, connective tissues, and pelvic organ structures. This represents a unified collaboration between the supportive and sphincteric muscle systems. The PM, being a circular skeletal muscle, leads us to hypothesize that under the circumstance of partial excision that does not compromise its entire circumferential structure and innervating nerves, its functionality should be largely preserved. This hypothesis was validated in patients 1 and 2 who were assessed for well-functioning PFMs. In patients 1 and 2, in whom the complete PM was preserved, postoperative defecation function was significantly better than that in patient 3, who had a partial excision of the PM. Patient 3 experienced frequent fecal incontinence, Patient 1 had almost no fecal incontinence, whereas patient 2 experienced fecal incontinence only 1–2 times per week. Besides, follow-up evaluations suggested that the broader the resection of the PFMs, the more suboptimal the defecatory function. In patient 1, part of the EAS was retained, whereas in patient 2, the entire anal sphincter was excised. During postoperative follow-up, patient 1's defecation function was significantly superior to that of patient 2. The same applies to ISR procedures; the more extensive the removal of the anal sphincter, the more impaired the defecatory function after surgery (16). Therefore, while ensuring R0 resection, the extent of PFM excision should be precisely determined to achieve optimal postoperative defecation function. This may require a decision based on the tumor's preoperative T stage and degree of intraoperative extramural invasion. As of June 2025, three patients showed no signs of metastasis or recurrence. The long-term efficacy awaits further follow-up.

We adhered to strict criteria when selecting patients for combined PPFMR and ISAR procedures. Based on the PM thickness reported by Singh et al. (17), the average thickness of the left and right PM was approximately 6.5 ± 2.04 mm and 4.9 ± 2.3 mm, respectively. Only those patients meeting the following criteria were deemed eligible for undergoing combined procedures of PPFMR with ISAR: a left PM thickness of ≥6·5 mm, a right PM thickness of ≥4·9 mm, and a modified Oxford score of ≥5 levels. Moreover, owing to the uncertainty surrounding postoperative outcomes, we exclusively performed PPFMR with ISAR in patients whose desire to retain their anus far surpassed their consideration for life itself after fully informing them of the pertinent postoperative risks. Simultaneously, a contingency plan should be prepared; in the event that postoperative anal function does not meet the required criteria, subsequent APR surgery should be performed. This encompasses the closure of the anus along with the colostomy-creation procedure, which constitutes a relatively straightforward surgical process.

In principle, patients with advanced-stage rectal cancer must receive neoadjuvant therapy preoperatively to shrink the tumor, thereby increasing the likelihood of preserving the anus and reducing local recurrence rates (5). However, neoadjuvant chemoradiotherapy can induce fibrosis in rectal and anal tissues, thereby significantly increasing the incidence of fistulas at the anastomotic site (18, 19). Compared to postoperative radiotherapy, neoadjuvant chemoradiotherapy may lead to more severe rectal and anal functional impairments (20), without a corresponding improvement in the 10-year overall survival (21). Considering all these, the patients undergoing PPFMR with ISAR did not undergo neoadjuvant chemoradiotherapy. Postoperative radiotherapy was administered based on individual circumstances, as exemplified in patient 3.

Presently, the assessment criteria for postoperative anal function include Wexner incontinence and LARS scores. Both scoring systems have limitations as they do not fully account for the practical feelings and needs of postoperative patients in their daily lives and their acceptance of defecation function. Therefore, we propose the concept of “acceptable postoperative defecation function (APDF)” defined as follows. First, the patient perceives the urge to defecate, can exert a certain degree of control over bowel movements, and has the time to address defecation matters, such as waiting until reaching a restroom. This essentially fulfills the requirements of daily life. Second, defecation function is reduced to some extent postoperatively; however, compared to having a colostomy bag, patients are satisfied with their postoperative defecation function.

According to data from current studies, patients with rectal cancer who received type IV ISR surgery (including complete resection of the IAS and partial resection of the EAS) achieved an average Wexner score of 9.0–11.1 points at a 5-year postoperative follow-up (22, 23). Patient 1 achieved a notable Wexner score of 7 points at 24 months postoperatively. She is an elderly retired woman who rarely ventures outside and generally remains within the confines of her residential community. She reported effective control of bowel movements with virtually no fecal incontinence and no need for pads. The surgical impact on the patient's daily life was minimal, and the results were remarkable. Although patients 2 and 3 experienced poor defecation function in the short-term after surgery, defecation function improved to some extent after 24 months of follow-up. Patient 2 achieved a Wexner score of 12 points, which was close to the average level observed after IV-type ISR surgery. He reported being able to suppress the urge to defecate for 3–5 min, allowing sufficient time to reach a restroom. However, his stools were occasionally unformed, and he experienced fecal incontinence one to two times per week. During business travel, the patient adopted a low-fiber diet to minimize stool output and used protective pads. Patient 3 had a Wexner score of 16. He is an elderly retired man who spends most of his time within his residential community. His daily needs were primarily addressed by his wife, although he was capable of living independently when she was not present. He reported that he was able to perceive the urge to defecate and could suppress it for up to 20 s. His bowel movements did not follow a fixed schedule, and episodes of fecal incontinence were frequent, necessitating the use of protective pads throughout the day. However, he occasionally reached the restroom during defecation. All three patients expressed overall satisfaction with their postoperative defecation function. This outcome confirms our hypothesis that patients with ULRC/ACC with good PFM function can maintain a satisfactory level of what we define as APDF after undergoing combined PPFMR with ISAR.

Currently, no surgical procedures ensure the perfect preservation of anal function. Among patients who undergo ISR, especially type IV ISR, a significant proportion who experience postoperative anal dysfunction or even anal incontinence remains (23). Part of the reasons may also be associated with the lack of rigorous preoperative assessment of patients' PFM functionality. In carefully selected cases, our surgical approach enabled patients to achieve APDF. Our surgical approach, combined PPFMR with ISAR, enables patients to attain APDF, with short-term oncological outcomes no worse than those of traditional APR surgery (24).

Patients with good pelvic floor function who strongly refuse permanent stoma can undergo a combination of partial pelvic floor muscle resection and in situ anal reconstruction. This enables a greater number of patients with ULRC or ACC to undergo curative oncologic surgery while preserving the APDF, thereby enhancing their overall quality of life. We will continue to expand the sample size and collaborate with other affiliated hospitals to conduct a multicenter prospective study. Patients will be further classified based on their varying lifestyles and tumor conditions to establish a comprehensive evaluation system to ensure quality of life following surgery.