Abstract Anal fistula is a common anorectal disease, and there is still a lack of uniform norms for the diagnosis and treatment of anal fistula. Large postoperative anal injuries and even the occurrence of anal incontinence can still be seen in clinical practice. Total sphincter preservation surgery is important to improve the cure rate and reduce postoperative anal functional impairment, but the use of total sphincter preservation surgery is not very widespread in current clinical practice. Anal fistula is an ancient and common anorectal disease, and the records of anal fistula treatment can be traced back to the Hippocratic era in the 4th century B.C., when horsehair was used for the treatment of anal fistula. The treatment of anal fistula has also been described in detail in the ancient medical text “The Complete Book of Ancient and Modern Medicine” and “The Authentic Book of Surgery”. In recent times, the understanding of the pathogenesis of anal fistula and the anatomy and physiology of the anus has developed rapidly, and there has been great progress in the diagnosis, classification and treatment of anal fistula. There are tens of thousands of clinical cases of anal fistula in China every year, but due to different levels and concepts of diagnosis and treatment, there is a lack of unified standards for the diagnosis and treatment of anal fistula, and the clinical treatment results vary greatly. Especially after some high complexity anal fistulas are cut and threaded, the anal function is greatly damaged. The importance of maintaining the normal physiological function of the anus has been deepened as the understanding of anal surgeons on the concept of anal fistula treatment has become more and more popular, and total sphincter preservation surgery has become a new direction of anal fistula treatment. The diagnosis of anal fistula is still mainly based on subjective clinical experience, and the use of intracavitary ultrasound and MRI is rare. Clinically, the diagnosis of anal fistula still relies mainly on the experience of individual physicians. Despite the obvious clinical presentation of most fistulas, only 48% of fistulas can be accurately diagnosed by history and simple physical examination. About 5% of fistulas contain multiple fistulas or fistulas located above the anorectal ring, and inadequate preoperative evaluation leads to residual fistulas or occult foci of infection during surgery as the main cause of postoperative fistula recurrence. In recent years, with the use of intracavitary ultrasound and MRI, the diagnosis of anal fistula has gradually transitioned from the traditional empirical diagnosis to objective imaging, and now MRI has become the gold standard for preoperative diagnosis of anal fistula. Preoperative intracavitary ultrasound or MRI can help detect hidden fistulas, and especially 3D ultrasound or MRI fistula imaging can further improve the accuracy of anal fistula diagnosis and reduce the recurrence rate of anal fistula after surgery. However, the preoperative diagnosis of anal fistula at home and abroad is still mainly based on personal experience and physical examination, and the proportion of intracavitary ultrasound or MRI used is not more than 10%. Due to the complexity of fistula diagnosis and treatment and the risk of potential anal incontinence, it is recommended that patients with suspected high-grade complex anal fistula should routinely undergo intracavitary ultrasonography or (and) MRI to clarify the extent and depth of the fistula and the relationship with the sphincter, which is important for guiding surgical treatment and postoperative follow-up. If preoperative anorectal manometry can be performed if available, it is also an important reference value for postoperative anal function prediction and postoperative follow-up. The most commonly used classification method abroad is the Parks classification of anal fistulae, while there is a lack of unified clinical diagnostic criteria in China, so the clinical data reported in China lack comparability The most commonly used international classification of anal fistulae is the Parks classification. The most important significance of this classification is that it classifies fistulas according to the relationship between the fistula and the sphincter, which allows the degree of damage to the sphincter to be understood during treatment, but it ignores the relationship between the “cavity” and the fistula that accompanies fistula treatment. Keigley et al. refined the Parks classification to be more instructive. In general, a clinically relevant classification is one that takes into account the relationship between the internal and external orifices, the fistula and sphincter, and the relationship between the fistula and the cavity in the diagnosis of anal fistula. At present, the diagnostic criteria for anal fistulas developed in 1975 are commonly used in China, which classify anal fistulas into high and low by the upper and lower anorectal rings, and into complex and simple by the number of external openings. Of course, the more external openings and fistulas there are, the more difficult the treatment will be, but not all fistulas with more than 2 external openings are very complicated to treat. In this classification criteria, the sphincter below the rectal ring of the anal canal includes the subcutaneous, superficial and deep external sphincter and most of the internal sphincter. If so much of the sphincter is severed during surgery, the patient may be at risk of anal incontinence. Therefore, in the determination of the location of fistulas in China, the extent of low anal fistulas is too large, and if these “low anal fistulas” are subjected to any kind of sphincterotomy, there may be a greater risk of anal incontinence. Nowadays, many hospitals still use this classic diagnosis of high anal fistula and complex anal fistula, but this diagnostic classification does not fully understand the relationship between the fistula and the anal sphincter, and the classification is not uniform and comparability between the literature is poor, which limits the significance of guidance in the treatment of anal fistula. 3.1 Different treatment goals should be set for different types of anal fistulas. There is still no unified standard for the treatment of anal fistula at home and abroad. However, there is a consensus that surgical treatment of anal fistula should focus on the protection of anal function and minimally invasive treatment whenever possible. In recent years, sphincter-preserving surgery, such as mucosal flaps or flaps, bioprotein gel closure, anal fistula embolization, and LIFT, is becoming the treatment of choice for complex anal fistulas. The cure rates of these methods have been reported in various studies, but sphincter-preserving surgery provides better preservation of anal function than conventional fistula surgery. The use of sphincter-preserving surgery as a treatment option for anal fistulas in Western countries is becoming more popular every year. In the English literature in the last 5 years, the proportion of sphincter-preserving surgery is 69.3%, while in China it is only 7.2%. The majority of authors still use the traditional methods of fistula excision or cutting and hanging, and although these methods play an important role in the treatment of anal fistula, these procedures may cause irreversible damage to anal function in patients. Therefore, total sphincter preservation surgery, as a new direction of anal fistula treatment, can reduce the chance of postoperative anal incontinence and should be the preferred technique for anal fistula treatment, while the traditional cut-and-wire method has more scar tissue and is likely to damage the sphincter and cause anal dysfunction, so it should be avoided as the last step of anal fistula treatment. The treatment of anal fistula should be chosen according to the principle of “function first, efficacy second”. Different treatment goals should be set for different fistulas: (1) for intersphincteric fistulas, the goal of treatment should be complete cure with no damage to anal function, and more perfectly, minimal scarring of the anal area; (2) for trans-sphincteric fistulas, try to choose a procedure with a high cure rate and maximum preservation of anal function; (3) for supra-sphincteric fistulas, any attempt to The aim of treatment is to minimize recurrent infections caused by fistulas, and the main goal is not to cure the fistula; ④ extra-sphincter fistulas are often secondary to anorectal injury, Crohn’s disease, pelvic tuberculosis, pelvic abscess and other diseases. Drainage is often the main goal, and specific treatment plans are set according to the specific situation. The choice of surgical method for anal fistula is consistent with the goal of surgery, and the key is to choose the right method for the right patient. The most basic procedures for anal fistula are anal fistulotomy and anal fistulotomy. Fistulotomy is often used for simple subcutaneous fistulas or intersphincteric fistulas, and surgical excision can even close the incision for those with good trauma conditions and shorten the healing time, but fistulotomy requires removal of all fistula tissue and is relatively invasive and unsuitable for more complex fistulas. For fistulotomy, the fistula is incised to cure the fistula. For fistulas with low location and small sphincter removal, incision can be performed directly; for fistulas with large incision, cutting and hanging wires are used to reduce the incidence of postincision anal incontinence. Although the incidence of severe anal incontinence decreases significantly with the use of cutting and hanging wires, there is still a certain incidence of mild anal incontinence, especially in cases where more than 1/2 of the external sphincter is incised, and postoperative anal function is affected to some extent. The literature reports a 30-50% incidence of anal incontinence after fistula incision or fistula incision and ligature surgery, and even patients who do not develop anal incontinence immediately after fistula surgery are at significantly increased risk of developing anal incontinence in old age. To reduce anal incontinence due to fistula surgery, do not attempt to cure some particularly complex anal fistulas, especially combined Crohn’s fistulas and tuberculous fistulas, which are often difficult to achieve by attempting to expand the surgery to achieve a cure. Total sphincter-preserving surgery is a new direction in the treatment of anal fistulas. The total sphincter-preserving procedure can reduce postoperative anal functional impairment, but reports of its clinical efficacy vary widely. Currently, the commonly used methods include bioprotein seal, anal fistula plug filling, drainage hanging, nudging mucosal flap or nudging skin flap, and ligation of trans-sphincteric fistula (LIFT). However, the success rate is only 10-30%, and the recent long-term follow-up study may be even lower and may be gradually abandoned; fistula plug is a new treatment method for anal fistula reported in recent years, with early reports of good short-term efficacy and a cure rate of more than 80%], but the cure rate is 13-50% in a large sample with long-term follow-up. However, this procedure also causes less damage to the sphincter muscle, and even if it fails, it can be reoperated without causing new functional damage to the anus; drainage threads are commonly used in the treatment of some difficult-to-cure anal fistulas such as Crohn’s fistula and tuberculous fistula, and their purpose is to keep the fistula drained and free from infection; pushed mucosal flaps and pushed skin flaps are more effective in the treatment of anal fistula. However, in some patients, it is difficult to create a mucosal flap or flap, and there is a possibility of necrosis and serious infection. The ligation of the intersphicteric fistula tract (LIFT) is a new completely sphincter-preserving procedure for the treatment of complex anal fistulas reported by Rojanasakul in 2007, which closes the internal opening by ligating and cutting the fistula in the space between the internal and external sphincters, preventing the source of infection in the rectum, scratching to remove the necrotic tissue in the external remnants of the fistula, and healing by The fistula is removed by scraping and removing the external residual necrotic tissue, and is drained to achieve healing. Rojanasakul et al. treated 18 cases of trans-sphincteric fistulas with LIFT, with a cure rate of 94.4% and an average healing time of 4 weeks. Aboulian et al. reported a success rate of 68% in the treatment of complex anal fistula with LIFT. These procedures suggest that LIFT procedure seems to be a highly desirable procedure.Hong searched Pubmed, Web of Science and Cochrane databases for articles related to LIFT procedure for anal fistula from January 2007 to March 2013 and collected 24 articles including 1100 patients. The mean postoperative follow-up was 10.3 months, with a mean cure rate of 76.4% and no postoperative anal incontinence. The cure and recurrence rates of LIFT reported by different research groups vary somewhat, which is due to different criteria for case selection, as well as other reasons such as differences in hospitals and surgeon proficiency. Although there are clinical reports of LIFT procedure in mainland China, most of them are small samples and lack of large sample randomized controlled studies. The author recently studied 128 patients with anal fistula in 4 clinical centers, divided into treatment group (LIFT procedure) and control group (anal fistula incision or incision and hanging) according to the randomized envelope method, with 66 cases in the treatment group and 62 cases in the control group. The cure rate of the treatment group was 86.36%, with mild postoperative pain, shortened wound healing time and good protection of anal function. The selection and treatment of the intersphincteric incision were improved, which reduced the complications such as intersphincteric infection and incision laxity and further improved the clinical efficacy. In general, LIFT has obvious advantages compared with other surgical methods for treating complex anal fistulas: it protects the anal sphincter, reduces tissue damage, shortens the healing time, has a small invasive surface, is simple to operate, and has no effect on secondary surgical treatment after recurrence. In summary, in the treatment of anal fistula, the relationship between the internal and external openings, the fistula and sphincter, and the relationship between the fistula and the cavity should be fully considered, and the principle of “function first and efficacy second” should be followed. It is necessary to consider carefully any surgical method that will damage a large area of the sphincter. Total sphincter preservation surgery is a new trend in the treatment of anal fistula, but a large sample of randomized controlled studies is still needed in clinical practice, which needs to be further explored and promoted.