Anal Fissure

Updated: Mar 29, 2023
Author: Lisa Susan Poritz, MD; Chief Editor: John Geibel, MD, MSc, DSc, AGAF 



An anal fissure (see the images below) is a painful linear tear or crack in the distal anal canal, which, in the short term, usually involves only the epithelium and, in the long term, involves the full thickness of the anal mucosa. Anal fissures develop with equal frequency in both sexes; they tend to occur in younger and middle-aged persons.

Failure of medical therapy is an indication for surgical therapy. Controversy mostly involves continued efforts to find a medical therapy for anal fissure that is as successful as the surgical therapy for the condition.

For patient education resources, see the Digestive Disorders Center, as well as Anal Abscess, Rectal Pain, and Rectal Bleeding.


A thorough knowledge of the anatomy of the anal canal is vital for effective surgical treatment of an anal fissure.

The anal canal may be defined in two ways, as follows:

  • Functional (or surgical) anal canal
  • Anatomic anal canal

These two terms are often used interchangeably, even though they do not mean the same thing. The surgical anal canal is approximately 4 cm long and extends from the anal verge or intersphincteric groove distally to the anorectal ring, proximally. The anatomic anal canal is only approximately 2 cm long and extends from the anal verge distally to the dentate line proximally.

The dentate line is the junction of the ectoderm and endoderm in the anal canal. The anal verge is an anocutaneous line approximately 2 cm distal to the dentate line. The anal verge marks the beginning of the anal canal.

The internal anal sphincter is a smooth muscle that is the most distal extension of the inner circular smooth muscle of the colon and the rectum. It is 2.5-4 cm long and is normally 2-3 mm thick. The internal sphincter is not under voluntary control and is continuously contracted to prevent unplanned loss of stool.

The external anal sphincter is striated muscle that forms a circular tube around the anal canal. Proximally, it merges with the puborectalis and the levator ani to form a single complex. Control of the external anal sphincter is voluntary.

Pathophysiology and Etiology

The exact etiology of anal fissures is unknown, but the initiating factor is thought to be trauma from the passage of a particularly hard or painful bowel movement. Low-fiber diets (eg, those lacking in raw fruits and vegetables) are associated with the development of anal fissures. No occupations are associated with a higher risk for the development of anal fissures. Prior anal surgery is a predisposing factor because scarring from the surgery may cause either stenosis or tethering of the anal canal, which makes it more susceptible to trauma from hard stool.[1]

Initial minor tears in the anal mucosa due to a hard bowel movement probably occur often. In most people, these heal rapidly without long-term sequelae. In patients with underlying abnormalities of the internal sphincter, however, these injuries progress to acute and chronic anal fissures. Studies of the internal anal sphincter and of anal canal physiology have been performed with varied results, but at least one abnormality is likely present in the internal anal sphincter of many anal fissure patients.

The most commonly observed abnormalities are hypertonicity[2] and hypertrophy of the internal anal sphincter, leading to elevated anal canal and sphincter resting pressures. The internal sphincter maintains the resting pressure of the anal canal; anal-rectal manometry can be used to measure this pressure. Most patients with anal fissures have an elevated resting pressure, which returns to normal levels after surgical sphincterotomy.

The posterior anal commissure is the most poorly perfused part of the anal canal. In patients with hypertrophied internal anal sphincters, this delicate blood supply is further compromised, thus rendering the posterior midline of the anal canal relatively ischemic. This relative ischemia is thought to account for why many fissures do not heal spontaneously and may last for several months.

Pain accompanies each bowel movement as this raw area is stretched and the injured mucosa is abraded by the stool. The internal sphincter also begins to spasm when a bowel movement is passed. This spasm has two effects: First, it is painful in itself, and second, it further reduces the blood flow to the posterior midline and the anal fissure, contributing to the poor healing rate.


Approximately 1-6% of patients have a recurrence of their anal fissure after sphincterotomy. The recurrence rate is higher after a sphincter stretch. If a patient develops a recurrence after a sphincterotomy, it could be from recurrent disease or from an improperly or incompletely performed initial sphincterotomy.

In the event of a recurrence, medical management should be attempted again, but if no relief is obtained, the surgeon must evaluate whether the original sphincterotomy was adequate. Evaluation can be performed by means of palpation during examination under anesthesia or by means of endoanal ultrasonography. If the sphincterotomy was incomplete, it can be completed on the initial side or redone on the opposite side. If the first sphincterotomy was complete, a second sphincterotomy can be completed on the opposite side.




Typically, the symptoms of an anal fissure are relatively specific, and the diagnosis can often be made on the basis of the history alone. However, like other common benign anal pathologic conditions, anal fissure is sometimes misdiagnosed or mistaken for another condition of this type.[3]

Typically, the patient reports severe pain during a bowel movement, with the pain lasting several minutes to hours afterward. The pain recurs with every bowel movement, and the patient commonly becomes afraid or unwilling to have a bowel movement, leading to a cycle of worsening constipation, harder stools, and more anal pain. Approximately 70% of patients note bright-red blood on the toilet paper or stool. Occasionally, a few drops may fall in the toilet bowl, but significant bleeding does not usually occur with an anal fissure.

Physical Examination

Initially, the fissure is just a tear in the anal mucosa and is defined as an acute anal fissure. If the fissure persists over time, it progresses to a chronic fissure that can be distinguished by its classic features. The fibers of the internal anal sphincter are visible in the base of the chronic fissure, and often, an enlarged anal skin tag is present distal to the fissure and hypertrophied anal papillae are present in the anal canal proximal to the fissure. (See the images below.)

Acute anal fissure. Acute anal fissure.
Anal fissure. Anal fissure.

Most anal fissures occur in the posterior midline, with the remainder occurring in the anterior midline (99% of men, 90% of women). About 2% of patients have anterior and posterior fissures. Fissures occurring off the midline should raise the possibility of other bowel conditions (eg, Crohn disease), infection (eg, sexually transmitted disease or AIDS[4] ), or cancer.



Laboratory Studies

If an ordinary anal fissure is suggested and if it is located in the posterior or anterior midline, then no laboratory tests are necessary.

If the fissure is off the midline or irregular, or if an underlying illness (eg, Crohn disease, squamous cell cancer, or AIDS[4] ) may be present, then the appropriate tests should be ordered; these may include the following:

  • Erythrocyte sedimentation rate (ESR)
  • Stool and viral cultures
  • HIV testing
  • Biopsy of the lesion or fissure (as warranted)

Diagnostic Procedures

The diagnosis of anal fissure can usually be made on the basis of findings from a gentle perianal examination with inspection of the anal mucosa, in conjunction with a good history. In this case, no diagnostic procedures are required. A digital rectal examination (DRE) is painful and often can be deferred.

Occasionally, the fissure is not easily visualized, and anoscopy is required to see it. However, anoscopy is not well tolerated by a patient with an acute anal fissure, and the procedure can often be deferred, with the patient treated solely on the basis of symptoms. Occasionally, a topical application of 1-2% lidocaine facilitates the examination.

Patients who do not heal, those who have relief from symptoms with appropriate therapy, or those who have a recurrent anal fissure after surgical therapy should be evaluated further with anoscopy and rigid proctosigmoidoscopy to exclude other pathologies. Patients with chronic fissures tend to have less pain and can better tolerate either anoscopy or rigid proctosigmoidoscopy and should have this included in their evaluation.

Histologic Findings

The fissure is not usually excised; therefore, no pathology specimen is available for examination. When it is excised, the tissue typically exhibits nonspecific inflammation. If some of the muscle is accidentally excised with the fissure, the internal sphincter usually demonstrates fibrosis.



Approach Considerations

Failure of medical therapy to resolve the acute fissure is an indication for surgical intervention. The presence of a symptomatic chronic fissure is also an indication for surgery because few of these heal spontaneously.

The main contraindication to surgery for an anal fissure is impaired fecal continence, a state that could be exacerbated by surgery. This contraindication mostly applies to patients with minor incontinence (occasional seeping).

Patients with gross fecal incontinence (solid material) rarely develop fissures; however, those with irritable bowel syndrome and incontinence to liquid stool can develop fissures if they become constipated. These patients are at the most risk for surgical treatment of an anal fissure, because their typical bowel pattern is loose and harder to control.

The American Society of Colon and Rectal Surgeons (ASCRS) has published clinical practice guidelines on the management of anal fissure.[5] The American College of Gastroenterology (ACG) clinical guideline on the management of benign anorectal disorders includes recommendations for chronic anal fissure.[6] (See Guidelines.)

Medical Therapy

Initial therapy for an anal fissure is medical in nature, and more than 80% of acute anal fissures resolve without further therapy. The goals of treatment are to relieve the constipation and to break the cycle of hard bowel movement, associated pain, and worsening constipation. Softer bowel movements are easier and less painful for the patient to pass.

First-line medical therapy consists of therapy with stool-bulking agents, such as fiber supplementation and stool softeners. Laxatives are used as needed to maintain regular bowel movements. Mineral oil may be added to facilitate passage of stool without as much stretching or abrasion of the anal mucosa, but it is not recommended for indefinite use. Sitz baths after bowel movements and as needed provide significant symptomatic relief because they relieve some of the painful internal sphincter muscle spasm.

Recurrence rates are in the range of 30-70% if the high-fiber diet is abandoned after the fissure is healed. This range can be reduced to 15-20% if patients remain on a high-fiber diet.

Second-line medical therapy consists of intra-anal application of 0.4% nitroglycerin (NTG; also called glycerol trinitrate) ointment directly to the internal sphincter.[7] Nitroglycerin rectal ointment is approved by the US Food and Drug Administration (FDA) for moderate-to-severe pain associated with anal fissures and may be considered when conservative therapies have failed.[8]

Some physicians use NTG ointment as initial therapy in conjunction with fiber and stool softeners, and others prefer to add it to the medical regimen if fiber and stool softeners alone fail to heal the fissure. NTG ointment is thought to relax the internal sphincter and to help relieve some of the pain associated with sphincter spasm; it also is thought to increase blood flow to the anal mucosa.

Unfortunately, many people cannot tolerate the adverse effects of NTG, and as a result, its use is often limited. The main adverse effects are headache and dizziness; therefore, patients should be instructed to use NTG ointment for the first time in the presence of others or directly before bedtime.

Analogous to the use of NTG intra-anal ointment, nifedipine ointment is also available for use in clinical trials. It is thought to have similar efficacy to NTG ointment but with fewer adverse effects.

Botulinum toxin (eg, onabotulinumtoxinA [BOTOX®]) has been used to treat acute and chronic anal fissures. It is injected directly into the internal anal sphincter, in effect performing a chemical sphincterotomy. The effect lasts about 3 months, until nerve endings regenerate. This 3-month period may allow acute fissures (and sometimes chronic fissures) to heal and symptoms to resolve.[9] If botulinum toxin injection provides initial relief of symptoms but there is a recurrence after 3 months, the patient may benefit from surgical sphincterotomy.[10, 11]

In a review of four prospective, randomized, controlled trials that included a total of 279 patients, Shao et al concluded that surgery—specifically, lateral internal sphincterotomy—was more effective than botulinum toxin injection for healing chronic anal fissures.[12] For surgery as compared with toxin injection, there was an absolute benefit increase rate of 23%, with toxin injection associated with a lower fissure healing rate and a higher recurrence rate. However, the incidence of minor anal incontinence was higher with surgery.

Surgical Therapy

Surgical therapy is usually reserved for acute anal fissures that remain symptomatic after 3-4 weeks of medical therapy and for chronic anal fissures.

Preparation for surgery

The administration of two Fleet enemas on the morning of the procedure is sufficient bowel preparation for surgical treatment of an anal fissure. If the fissure is too painful, the enemas may be omitted. No other preoperative preparation is necessary unless the patient has significant comorbidities that require attention.

Procedural details

Sphincter dilatation

This procedure is a controlled anal stretch or dilatation under general anesthetic. It is performed because one of the causative factors for anal fissure is thought to be a tight internal anal sphincter. Stretching the tight sphincter helps correct the underlying abnormality, thus allowing the fissure to heal. The number of fingers used and the amount of time for which the stretch is applied vary among surgeons.

Although the sphincter stretch does provide symptomatic relief from the anal fissure, it is rarely performed today, because of the high complication rate. Impaired continence is observed in 12-27% of patients as a consequence of uncontrolled stretching and subsequent tearing of the internal and external sphincter.

Lateral internal sphincterotomy

Lateral internal sphincterotomy is the current surgical procedure of choice for anal fissure. The procedure can be performed with the patient under general or spinal anesthesia. (Local anesthesia may even be used in the cooperative patient, though it is not always recommended). The purpose of the operation is to cut the hypertrophied internal sphincter, thereby releasing tension and allowing the fissure to heal.[13]

When first described, sphincterotomy was performed in the posterior midline at the site of the fissure, with or without a fissurectomy.[14] However, the incision for the sphincterotomy usually did not heal, for exactly the same reason that the fissure did not heal. Currently, sphincterotomies are normally performed in the lateral quadrants (right or left, depending on the comfort or handedness of the surgeon). In a properly performed lateral internal sphincterotomy, only the internal sphincter is cut; the external sphincter is not cut and must not be injured.

The sphincterotomy can be performed in either an open or a closed manner, as described below.

In a closed sphincterotomy, a No. 11 blade is inserted sideways into the intersphincteric groove laterally. It is then rotated medially and drawn out to cut the internal sphincter. Care is taken not to cut the anal mucosa, because doing so could result in a fistula. After the knife is removed, the anal mucosa overlying the sphincterotomy is palpated, and a gap in the internal sphincter can be felt through it. The sphincterotomy is extended into the anal canal for a distance equal to the length of the anal fissure.

In an open sphincterotomy, a 0.5- to 1-cm incision is made in the intersphincteric plane. The internal sphincter is then looped on a right angle and brought up into the incision. The internal sphincter is then cut under direct visualization. The two ends are allowed to fall back after being cut. A gap can then be palpated in the internal sphincter through the anal mucosa, as in the closed technique. The incision can be closed or left open to heal.

When treating a chronic anal fissure, the surgeon may elect to perform a fissurectomy in conjunction with the lateral sphincterotomy. In such cases, care must be taken not to include a piece of the internal sphincter with the excision. More simply, instead of excising the fissure along with the sphincterotomy and worrying whether it will heal, the surgeon can excise the hypertrophied papillae and the skin tag and leave the fissure to heal on its own.

Sometimes, long-standing chronic fissures do not heal, even with an adequate sphincterotomy, and an advancement flap must be performed to cover the defect in the mucosa. This can be performed either at the time of the sphincterotomy if the surgeon does not think that the fissure will heal or as a second procedure if the fissure does not heal.

Postoperative Care

Sphincterotomy is performed either in an outpatient setting or as an office procedure, and patients return home the same day. Typically, minimal postoperative pain is associated with either the closed or the open technique—usually no more than the fissure caused preoperatively. Pain from the fissure starts to abate almost immediately. The only postoperative restrictions are from the anesthetic, and many patients can return to normal activities the following day.


Complications from surgery for anal fissure include the following:

  • Infection
  • Bleeding
  • Fistula development
  • Incontinence (the most feared complication)

Infection after sphincterotomy is rare and occurs as a small abscess in only 1-2% of patients, despite the inherent uncleanliness of the area. Treatment is drainage of the abscess. Antibiotics are necessary only if significant associated cellulitis occurs or if the patient is immunosuppressed.

Some ecchymosis may occur around the sphincterotomy site, but bleeding that necessitates therapy is extremely rare.

Fewer than 1% of patients develop an anal fistula at the site of the sphincterotomy. This usually results from a breach of the mucosa at the time of the sphincterotomy. The fistula is often low and superficial and should be treated with fistulotomy.

The incidence and definition of incontinence vary dramatically from study to study and among the different procedures. Of patients undergoing the sphincter stretch, 12-27% report problems with continence after the procedure. This is most likely because this is an uncontrolled stretch of the anal sphincter and because both the internal and external sphincters are stretched.

Incontinence rates are much lower with a properly performed internal sphincterotomy than with sphincter stretch, though these rates depend on the definition of incontinence being applied. In most patients, the minor soiling or incontinence to flatulence that may occur in the immediate postoperative period usually resolves without any long-term sequelae.

The recurrence or nonhealing rates for anal fissures after surgical treatment are in the range of 1-6%. Several studies found that as many as 50% of subjects who did not heal had underlying undiagnosed Crohn disease as the etiology for their fissure.

Long-Term Monitoring

Prescribe stool softeners and fiber supplementation after the surgery, and recommend fiber supplementation indefinitely to prevent future problems with constipation. Follow-up care usually consists of a single postoperative visit to ensure that the wound is healing appropriately and that the fissure has resolved.



ASCRS Clinical Practice Guideline on Anal Fissure

In 2023, the American Society of Colon and Rectal Surgeons (ASCRS) published updated guidelines on management of anal fissure, which included the following:

  • Nonoperative treatment of acute anal fissures is safe and should typically be first-line treatment.
  • Topical nitrates may be employed for treatment, but headache symptoms may limit their efficacy. Calcium-channel blockers (CCBs) are comparably efficacious for chronic anal fissures, have a better side-effect profile, and can be used as first-line treatment.
  • Botulinum toxin is comparable to topical therapies as first-line treatment for chronic anal fissures and yields modestly improved healing rates as second-line treatment after failed topical therapy.
  • Lateral internal sphincterotomy (LIS) may be offered to selected patients with chronic anal fissure who have not been treated pharmacologically. It is the treatment of choice for chronic anal fissures in selected patients without baseline fecal incontinence (FI).
  • Either open or closed techniques may be used for LIS; results are similar. Compared with traditional LIS extending to the dentate line, LIS tailored to fissure length yields similar healing rates and lower FI rates.
  • Limited short-term outcome data suggest that repeat LIS or botulinum injection for recurrent anal fissure yields good healing rates with a low risk of FI.
  • Anocutaneous flap is a safe surgical alternative for chronic anal fissure, with healing rates comparable to those of LIS and a lower risk of FI. Addition of an anocutaneous flap to botulinum toxin injection or LIS may decrease postoperative pain and allow for primary wound healing.

ACG Clinical Guideline on Anal Fissure

The 2021 American College of Gastroenterology (ACG) clinical guideline on the management of benign anorectal disorders made the following recommendations for chronic anal fissure[6] :

  • In general, management of chronic anal fissure consists of stool softening and spasm reduction for improved regional perfusion.
  • It is strongly recommended that initial medical treatment of chronic anal fissure be local application of a CCB.
  • A trial of botulinum toxin A injections is suggested in the setting of failed CCB therapy or as an alternative option to CCB. Another treatment option for chronic anal fissures is nitroglycerine.
  • LIS is strongly recommended as the surgical treatment of choice for chronic anal fissures refractory to nonsurgical measures.

Questions & Answers


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