The management of high complex anal fistulas presents a formidable challenge to colorectal surgeons worldwide (1). This condition, characterized by its complex anatomical pathways, has the potential to result in a high rate of recurrence, as well as incontinence and other significant complications. High transsphincteric anal fistula (HTAF) is a complex anal fistula that accounts for 30% of all anal fistulas; it passes through the internal anal sphincter (IAS) and involves more than one-third of the external anal sphincter (EAS) (2, 3). The deep intersphincteric space (DPIS) is a crucial anatomic site in the propagation of complex cryptoglandular anal fistulas, which play an important role in the formation of HTAF (4, 5). In particular, the primary infection originating from the anal glands tends to propagate toward the DPIS. Subsequently, HTAF is formed when the sepsis traverses the IAS and EAS and reaches ischiorectal fossa (6, 7). Precise knowledge of the exact position of the anal fistula and its relation with the anatomical structures is essential for the successful treatment of HTAF.

Fistulotomy is universally accepted and widely used to treat simple anal fistulas. However, the aggressive laying-open technique may cause unavoidable harm to the anal sphincter, leading to different levels of postoperative incontinence (8). With the development of surgical techniques, the treatment of anal fistulas has ranged from straightforward standardized incision and drainage to very complex sphincter-sparing procedures. These innovative techniques include ligation of the intersphincteric fistula tract (LIFT) (9); endorectal advancement flap (10); video-assisted anal fistula treatment (11); and anal fistula plug (12), and the injection of autologous centrifuged adipose tissue (13). Despite these advances, their long-term performance often fails to meet expectations. Closed trans-intersphincteric fistulotomy (CTIF) is an innovative surgical technique developed from LIFT (9), representing a progression for treating of HTAF. This technique, characterized by its conservative approach to the the anal sphincter complex, involves excising the intersphincteric fistula and associated infection via an intersphincteric approach while also addressing the primary internal opening. Subsequently, the IAS is meticulously sutured in a continuous manner to maintain its barrier function and minimize the likelihood of the constant presence of stool at the surgical site. Secondary healing is accomplished through the implementation of proper drainage of the intersphincteric incision. This study evaluated the safety and efficacy of CTiF technique in treating HTAF through a comprehensive analysis of clinical outcomes.

Total 60 patients with HTAF were prospectively enrolled and treated with CTIF. Three patients were lost to follow-up before the 6-month visit, and 2 patients with an anal fistula associated with Crohn's disease were excluded; thus, 55 patients were ultimately included in this study (Figure 3). The ratio of male/female was 51/4; the mean age was 36.04 ± 9.80 years; the mean body mass index was 24.34 ± 3.12 kg/m²; 3 (5.45%) patients had diabetes; and 7 (12.73%) patients had hypertension. Patient characteristics are shown in Table 1. The mean surgical duration was 28.6 ± 4.58 min. Four (7.27%) patients showed postoperative urinary retention: one was administered an intramuscular neostigmine injection, and the other three were catheterized. Details of the surgery are shown in Table 2.

At the 6-month follow-up, the CCF-FIS and VAS score were 0 [(0,0) range, 0–3] and 0 [(0,1); range, 0–4], respectively. The main results are shown in Table 3. During a mean follow-up period of 9.3 months (SD 1.81; range, 6–15), 50 (90.91%) patients recovered after the CTIF procedure, and there was recurrence of symptoms in 5 (10.91%) patients. The mean time to recovery was 7.09 ± 1.94 weeks. Among these 5 recurrent fistulas, 2 had impaired healing of the internal opening at 5 weeks and 6 weeks after surgery, and 3 patients had sepsis in the intersphincteric plane due to poor drainage at 4 weeks, 5 weeks, and 7 weeks. Two recurrent patients recovered after treatment with a TROPIS procedure, and three recovered after seton placement. No patient had anal incontinence.

HTAF tracts are complex. Their formation is closely related to the unique anatomical factors that make them prone to infection and spreading. Zhang et al. (5) conducted a retrospective MRI analysis of 508 patients with anal fistula and found that DPIS is often involved in complex posterior cryptoglandular fistulas and is involved in 80.1% of cases with HTAF. Chronic inadequate drainage of sepsis within DPIS is a principal factor contributing to recurrent postoperative episodes (18, 19). Therefore, DPIS is crucial during and after surgery in the management of HTAF.

Conventional surgical interventions, which involve extensive resection of the anal fistula, inflict considerable damage on the anal sphincter, precipitating incontinence and protracted recovery. Although recent advances in sphincter-preserving methodologies have been recognized for their safety, the results of these procedures are variable and fail to show the superiority of one procedure over another (20). The persistent risk of potential damage to the anal sphincters, along with the subsequent adverse functional outcomes, remains significant in patients with HTAF. Currently, transsphincter anal fistulas are primarily treated with the LIFT procedure. Nevertheless, this surgical approach is predominantly advisable for transsphincter anal fistulas without another branch, and it carries a high risk of long-term recurrence. Sun et al. (21) estimated that the LIFT procedure cure rate for treating HTAF ranges 25%–92%. In contrast to the ligation of fistulas by the LIFT procedure, tunnel resection was performed on fibrotic fistula tracts from the intersphincteric plane to the external opening in our surgery. Moreover, high anal fistula requires continuous adequate drainage of pus after surgery until the cavity is completely healed; therefore, we expected that opening the intersphincter plane would have a more beneficial effect.

In 2017, Garg et al. (22) focused on the treatment of the sphincter space and proposed a new sphincter-preserving operation: the TROPIS procedure. The fistula and internal opening were treated by direct incision of the mucosa from the internal opening to outside the IAS, deroofing the intersphincteric space from the luminal side. In a long-term follow-up study, however, it was found that the one-time cure rate of the TROPIS procedure in the treatment of high complex anal fistula was only 78.4% (23). Upon investigation, the author believes that the recurrence may be related to the failure to accurately locate the internal opening and thoroughly remove the intersphincteric fistulous tract. Mei et al. (17) found that an unidentified internal opening significantly correlated with the recurrence of anal fistula after surgery (relative risk, 8.54).

CTiF divide the surgical site into two parts: the IAS part and the EAS part, based on the intersphincteric space. In the intersphincteric space, the internal opening can be found more accurately along the direction of fistula, so as to reduce the risk of postoperative recurrence. Although we cut a small portion of the IAS during the operation (similar to the TROPIS procedure), we preserved the EAS and performed reconstruction and suturing of the IAS. The impact on anal function is minimal, and the study results have confirmed this. In addition, the IAS should be sutured to maintain the barrier effect of the IAS. Continuous suture with absorbable suture is a common choice, because absorbable suture can reduce the discomfort and complications of postoperative suture removal. When suturing, it is necessary to ensure the tightness and tension of suture is moderate to avoid postoperative complications such as fistula recurrence or anal stenosis. Within the scope of this study, we explored CTiF as a novel, sphincter-conserving stratagem, demonstrating its viability and safety. Remarkably, this technique achieved a healing rate of 90.91% (50 of 55 cases), with a median recuperation timeframe of 7.09 weeks during the mean follow-up period of 9.3 months. The outcomes were superior relative to existing sphincter-sparing approaches. Furthermore, given that anal fistulas may arise from diverse factors, such as anastomotic fistulas caused by colorectal cancer surgery and rectovaginal fistulas resulting from perineal colostomies, it is crucial to closely monitor this complication (24). Butyrylcholinesterase, serving as a new predictive biomarker of postoperative complications following colorectal surgery, can be considered to detect the recurrence of anal fistulas (25). The CTiF treatment points are discussed below.

CTIF is a safe and effective sphincter-sparing technique for managing HTAF and is worth clinical promotion. Further multicenter, randomized controlled trials comparing CTlF with other techniques and involving larger sample sizes are required to confirm the effectiveness and safety of this procedure.