Anal fissure is a small longitudinal ulcer formed by a fissure in the anal canal or anal margin, which can extend from the skin-mucosal junction to the dentate line. It is characterized by periodic pain during fecal evacuation, a small amount of fresh bleeding during fecal evacuation, and constipation with or without constipation. Anal fissures can occur at any age, but are most common in young adults, with no significant difference in incidence between men and women. More than 90% of anal fissures are located in the posterior midline of the anal canal. Anterior fissures are more common in women, but not more than 10%, and only 1% of male fissures are anterior fissures. The presence of inflammatory bowel disease, especially Crohn’s disease, should be considered when anal fissures occur in an abnormal area especially when there are multiple fissures on the lateral side. Clinically, anal fissures are often divided into acute and chronic fissures. Acute fissures are short in onset, have a light red base, fresh and neat fissures, and no scar formation, and can mostly heal on their own. In contrast, chronic anal fissures are recurrent, have a long duration, and the fissures are deep and uneven, often forming the typical anal fissure triad: well-defined, limited anal canal ulcers, hypertrophic anal papillae and anterior sentinel hemorrhoids. The etiology and pathogenesis of anal fissures In general, the etiology and pathogenesis of anal fissures are unknown, but current research indicates that the following factors are closely related to the occurrence of anal fissures. The usual theory is that repeated injury to the anal canal from hard fecal blocks during chronic constipation leads to chronic ulcer formation, but studies have shown that only 25% of patients with anal fissures have a history of constipation, while a significant number of patients have an increased number of combined stools or diarrhea. It is possible that the high anal canal resting pressure caused by constipation or diarrhea is a high risk factor for the development of anal fissures. Local anatomy Many studies have shown that the posterior mucosa of the anal canal has the weakest support and poor stretchability pulling the posterior anal mucosa blood volume less than other parts of the anal canal, while the anal mucosa blood volume at the anal fissure is also lower than normal population. This suggests that anal fissures may be caused by local ischemia. 3. Infection Chronic inflammation near the dentate line spreads downward and forms an abscess, which breaks down and becomes a chronic ulcer. Surgical treatment of anal fissure When conservative treatment is ineffective or recurrent, surgical treatment should be adopted. 1.Anesthesia for anal fissure surgery Most of the anal fissure surgeries can be performed in the outpatient clinic using local infiltration anesthesia. When fissures, abscesses and hemorrhoids are combined, we often use sacral block or epidural block, which can achieve satisfactory anesthesia. Usually general anesthesia is not necessary because appropriate preoperative and intraoperative medications have adequate sedative, anxiolytic, and amnesic effects. Usually diazepam (Valium) 10mg or thiopirid 0.1mg is injected intramuscularly 0.5-1 hour before surgery to provide preoperative anxiety and postoperative pain relief. Intraoperative administration of appropriate amount of propofol or fentanyl combined with midazolam (imipramine) under close respiratory and circulatory monitoring can achieve satisfactory sedation and amnesia. Postoperative local injection of long-acting lidocaine or the addition of non-steroidal anti-inflammatory drugs nano-anal, can significantly reduce pain. 2, surgical treatment (1) anal canal dilation Recamier was the first to apply this method to treat anal fissure in 1838. After anesthesia, the finger of one hand is inserted into the anal canal, followed by the finger of the opposite hand, and the two fingers are gently pulled on both sides for 30 seconds, followed by the middle fingers of both hands, and the four fingers are carefully dilated for 4-5 minutes. Some hospitals also use anal canal retractors or airbags to dilate the anal canal. This method is effective and simple in relieving the symptoms of anal fissure, but it is easy to recur, and the degree of dilatation is not easy to control because the internal and external sphincters are dilated at the same time, and it is difficult to avoid damage to the ability to control exhaustion and defecation. In the last 10 years or so, this method has been replaced by internal sphincterotomy. (2) Internal sphincterotomy The internal sphincter is a continuation of the distal part of the rectal cricothyroid muscle, which is an involuntary muscle and prone to spasm and contraction. There are 2 main methods of internal sphincterotomy. ① Posterior internal sphincterotomy This method cuts the lower edge of the internal sphincter directly through the anal fissure, from the anal edge to the dentate line, and sometimes also cuts the lower part of the external sphincter to facilitate drainage, and the wound opens and heals on its own. In case of combined external hemorrhoids and hypertrophic papillae, they can be removed at the same time. This method is effective, and Han Jinlin-40 in China has reported treating 60 cases all in one time without recurrence. However, this method is slow to heal and is prone to the formation of furrow scarring, which leads to “keyhole”-like deformities and about 5-10% of defecation disorders, so it should be handled with caution for those with flaccid anus. The lateral internal sphincterotomy is divided into two techniques: closed and open, usually at 3 or 9 o’clock laterally. Closed: An ophthalmic cataract scalpel or other small sharp knife can be inserted from the lateral muscle question groove of the anal canal and the internal sphincter can be incised from the lateral to the medial side. The knife can also be inserted from under the mucosa and cut laterally to the intermuscular sulcus. The blade is withdrawn and finger pressure is applied to break the remaining sphincter fibers, and no special treatment of the wound is required. The advantage of this procedure is that it is less painful and quicker to recover, but there is a risk of incomplete muscle severance and it is suitable for an experienced surgeon to operate. Open type: After touching the intersphincteric sulcus with the finger, an arc-shaped incision of about 1.5 cm in length is made about 1em lateral to the anus, and a curved vascular clamp is used to penetrate from the incision to the sphincter question sulcus up to the dentate line, and the slightly white inner sphincter fibers are picked up and cut under direct vision. The advantage of this procedure is that it can be performed under direct vision, hemostasis is complete, and tissue is taken for biopsy. ③Anal fissure excision is suitable for those with large defects in the anal canal skin and anal fissure combined with anal stenosis. A shuttle-shaped incision is made in the anterior and posterior middle of the fissure, and if combined with anterior sentinel hemorrhoids and anal papillae hypertrophy, they can be removed at the same time. Liao Xingzhong et al. “1 modified it by suturing the longitudinal incision appropriately, while the length of the transverse incision remains the same, but the central incision is not sutured and a radial incision is reserved for drainage in the lower part of the incision, which seems to reduce the tension of the transverse incision and accelerate healing. In addition, routine lateral internal sphincterotomy can reduce long-term recurrence. ④ Hanging sutures For anal fissures with fistulae. A round needle with a 10-gauge double-stranded silk thread is inserted from the outer edge of the fissure and exited from the internal sphincter to the inner edge of the fissure, and the silk thread is tightened and knotted. This procedure is performed simultaneously with incision and drainage without changing the medication, and there is less bleeding and less trauma during the procedure, but the patient often needs painkillers after the procedure. ⑤ flapplasty is mainly used for chronic anal fissures or anal ulcers with a high degree of scarring of the anal canal stenosis with the typical anal fissure triad. First, the stenotic part of the anal canal is incised, the base of the fissure ulcer is completely removed, the slightly white internal sphincter is cut, and care is taken to avoid damaging the red external sphincter. At a distance of 1-2 cm from the lower edge of the wound, a V-shaped incision is made parallel to the wound edge, and only the epidermis and dermis are cut, avoiding cutting into the subcutaneous fat, and the flap is intermittently sutured to the rectal mucosa in full. This procedure is faster and less painful due to phase I coverage of the fissure after excision and fewer complications, but occasional anal incontinence occurs. Note that this procedure does not alleviate the problem of sphincter spasm. Current studies confirm that severe local ischemia of the anal canal caused by sphincter spasm at the base of the anal fissure is the main cause of anal fissure. Various modalities of surgical treatment are also basically aimed at relieving the internal sphincter spasm. The current surgical treatment is complicated and diverse, and it seems that the clinical treatment results reported by various units are satisfactory, but the actual situation may not be so optimistic. Clinically, anal fissures can be combined with various complex conditions such as sinusitis, anal papillomegaly, internal and external hemorrhoids, fistulas, diarrhea, and constipation, and treatment should be individualized according to the patient. In addition, there is no uniform understanding and standard of various surgical methods, including the extent of surgical access and sphincter severance, and how to reduce complications such as anal incontinence and changes in anal morphology, which need to be further studied by colleagues in clinical work.