The data from our single-center study demonstrate the feasibility and safety of the BEAS technique, with a favorable overall cure rate of 93.75% during the 6-month follow-up period, which was comparable to that reported in our previous initial study [16]. The overall in-hospital complication rate was 2.78%, and no other major complications were noted. The recurrence rate was 6.25%, all of which ended in a smooth recovery after timely surgical management. Moreover, the BEAS technique seems superior to other techniques, such as the endorectal advancement flap, modified LIFT technique and autologous adipose-derived stem cell therapy, in terms of success rate and functional outcomes [22–24].
HHAF is characterized by a highly located internal opening, complex fistula extension and high recurrence rate. Sepsis usually spreads unilaterally or bilaterally from DPIS and DPAS along the midline and even spreads to the gluteus maximus through the ischiorectal fossa.
Adequate drainage of DPIS and DPAS and keeping them open until the spaces closed are highly significant. Due to the extensive involvement of the anal sphincter, adequate drainage of the open wound is bound to damage the anal sphincter, resulting in anal incontinence. In other words, a balance must be struck between adequate drainage and anal sphincter protection. Reasonable treatment of the fistula and proper management of the DPIS and DPAS while preserving anal function is the ideal result for the treatment of HHAF. Unfortunately, so far, no procedure can solve all three problems at the same time. In addition, the internal opening of HHAF varies substantially from that of common anal fistulas. It is often located in the anterior and posterior midlines, and its height is often more than one-third that of the sphincter complex. If transanal internal sphincterotomy or the cutting seton procedure is used to manage the internal openings, it will result in a large wound and take a long time to heal after operation.
According to the above characteristics of HHAF, we can summarize four basic principles for the treatment of HHAF. First, the integrity of the external sphincter should be protected. Second, the internal openings should be managed properly. Third, the DPIS and DPAS should be closed or reduced. Finally, the purulent cavity should be fully drained.
The results of this study show that the BEAS procedure was effective and safe for the treatment of HHAF, with an overall healing rate of 93.75% and no incontinence. Three patients (6.25%), which were suprasphincter fistula, include 1 circular HHAF and 2 posterior HHAF experienced recurrent symptoms. One patient with posterior HHAF was recovered after redo BEAS. The advantages of the BEAS procedure are discussed below.
First, the function and normal anatomical structure of the anal sphincter is preserved. A clear perianal and sphincter anatomy is helpful for the localization of HHAF. MRI is the standard modality for evaluating anal fistulas, as it helps define the anatomical structure and guide surgical treatment planning. Perianal MRI can accurately show the extent of inflammation preoperatively, while it is difficult to determine the scope of HHAF by digital rectal examination or perianal or endorectal ultrasound [25]. MRI is also helpful in finding abscess cavities or blind fistulas, which are prone to be missed during surgery. At the same time, MRI also helps to clarify the relationship between fistula and sphincter, which helps to prevent sphincter injury during surgery. The protection of anal sphincter function, especially EAS function, is one of the most critical determinants of long-term surgical success after surgery. Through two approaches (intersphincter approach and lateral-external-sphincteric approach), the EAS could be isolated and freed, which can be well protected during the operation. The results of our study showed that the average CCF-IS score on POD 180 (6 months after operation) was 1.29 (SD 2.87; range, 0–13), suggesting that the EAS and the anal function were well preserved.
Second, the internal opening should be completely closed. We shifted the musculocutaneous flap of the internal sphincter towards the distal side to dislocate the internal opening and fistula. This process was equivalent to sealing the internal opening with a patch from the patient's own tissue. In contrast with biological agents, there is no possibility of rejection after this operation. It can avoid the recurrence caused by incomplete closure of the internal opening.
Third, the involved posterior anal space should be effectively closed. We shifted the bare EAS towards the proximal side, thus blocking the connection between the internal opening and the DPIS or DPAS. Then we sutured and fixed the EAS and the musculocutaneous flap with absorbable suture to close the DPIS and reduce the DPAS.
Fourth, continuous and adequate drainage is necessary after the operation. The drainage of the DPIS and the DPAS is also a critical determinant of the success of the operation. Although the shift of the EAS can close the DPIS and shrink the DPAS to some extent, it is still necessary to drain the abscess. Because the internal opening is closed, the infection can be eradicated from the source. Next, the cure of HHAF only requires continuous and adequate drainage. We should keep the LES approach open with a proper-length incision and confirm that the approach will lead to the cavity, facilitating the replacement of drainage after the operation.
Fifth, the overall healing time can be shorter than the times of other treatments. Since no tissue is removed and no cutting seton is performed during the operation, a small wound can be achieved, and the healing time can be shortened. Patients can return to normal life earlier with less pain.
Finally, the procedure is much easier and less expensive. With the clear understanding of perianal and sphincter anatomy, it is easy and quick to perform the procedure.
Still, there are several limitations to our study. This was a single-center study with a small sample size, which limits the external validity and repeatability of our results. When evaluating the success of wound healing and wound closure, subjective judgments were made. Postoperative MRI, re-epithelialization of wound tissue and other objective indicators were lacking in our current study. Finally, our study was an initial clinical observational study. Further controlled clinical trials are needed to determine the effectiveness and safety of this procedure.
In summary, BEAS is effective in the treatment of primary or recurrent HHAF. Although BEAS achieves a lower short-term recurrence rate, the long-term recurrence rate still needs to be investigated. This procedure is worthy of further promotion and application.