Pediatric Fistula-in-Ano 

Updated: Aug 27, 2021
Author: Jayant Deodhar, MD; Chief Editor: Harsh Grewal, MD, FACS, FAAP 


Practice Essentials

A fistula is an abnormal communication between two epithelial-lined organs. A fistula-in-ano is a fistulous connection on the body surface near the anus. It is usually secondary to perianal infections (ie, acquired); in rare cases, it is secondary to a congenital defect.[1]  In an acquired fistula-in-ano, the communication is typically between the anal canal and the perineal skin. In a congenital fistula-in-ano, the fistulous tract may extend from the anal canal to the vestibule, vagina, or urethra.

As a clinical entity, fistula-in-ano has well been recognized from ancient times. Hippocrates (c. 460 BCE) used a seton to cure fistula-in-ano. The great Indian surgeon Sushruta (c. 1600 BCE) used a caustic ligature (kshara sutra) to treat fistula-in-ano. In 1337, John Anderne was the first to surgically lay open a fistula-in-ano.

Asymptomatic fistulae require no treatment. Medical therapy includes antibiotics and analgesics; in addition, treatment of the cause (and underlying tuberlculosis, if present) is necessary. Surgery is required if pain is severe, if medical treatment fails, or if the fistula-in-ano recurs. 


The anal canal is the part of the hindgut that extends from the anal ring to the anal verge. (See the image below.) The dentate line, which is the site of the cloacal membrane, divides the anal canal into the proximal part, lined by columnar epithelium, and the distal part, lined by squamous epithelium. At the level of the dentate line, transverse folds of mucosa form a ring of valves with pockets called the crypts of Morgagni. The anal glands open in the crypts. The glands branch out and lie in the submucosal plane or, most frequently, in the intersphincteric plane.

Anatomy of anal canal and perianal space. Anatomy of anal canal and perianal space.

For more information, see Anal Canal Anatomy.


In the congenital form of fistula-in-ano, the fistulous tract is lined with stratified squamous epithelium, columnar epithelium, or both. The acquired form manifests with repeated perianal abscesses and has an inflamed fibrous tract lined by granulation tissue and no epithelial lining upon microscopic examination.

In the infected (acquired) form, the crypts of Morgagni are deeper (3-10 mm) than normal (1-2 mm). This abnormality facilitates the trapping of bacteria, which cause cryptitis that leads to perianal abscess formation and fistulae. Abnormal anal glands[2] and hormonal imbalances have been described.


The congenital type is an uncommon developmental defect. The acquired type is secondary to a perianal abscess, tuberculosis (in developing countries), Crohn disease, or immunocompromise.

Abnormal anal glands[2]  and hormonal imbalances have also been proposed as causes of fistula-in-ano. Androgen excess may stimulate the sebaceous glands, resulting in secondary infection.


Fistula-in-ano is not common in children as compared with adults; most cases occur in adults. Fistula-in-ano is more common in boys than in girls, and 96% of cases occur in infants younger than 1 year.

At King Edward Memorial (KEM) Hospital in Pune, India, this condition is present in 0.18% of admitted patients.


Outcome is good for both acquired and congenital varieties of fistula-in-ano. Recurrence and scarring are common in patients with tuberculosis or Crohn disease.[3]

In a retrospective study of fistula-in-ano in children, Novotny et al demonstrated that recurrence is more likely in older children and in children who had previous episodes of perianal abscess or if pus was noted at the time of surgery.[4]

A study by Inoue et al reported good long-term success rates with seton placement in infants with fistula-in-ano and suggested that this procedure may be a useful treatment option in this population.[5]

In infants, fistula-in-ano and perianal abscesses tend to be self-limiting; in older children, the natural histories of these conditions are more similar to those seen in adults.[6]



History and Physical Examination

Congenital fistula-in-ano

Newborns with fistula-in-ano may or may not have an anus as part of the spectrum of imperforate anus. Male neonates may pass meconium per the urethra through a fistula located in the perineum, usually anterior to the normally located anus. In female neonates, meconium can be passed through the vagina, vestibule, or perineum. Both boys and girls present with recurrent urinary tract infection if fistula-in-ano is untreated.

Acquired fistula-in-ano

More than 96% of cases occur in infants younger than 1 year. The usual presentation involves a recurrent perianal abscess, which may or may not have been surgically treated.[7, 8]

Two distinct views have been expressed regarding perianal abscess and fistula-in-ano. In the first view, perianal abscess is regarded as a precursor to fistula-in-ano. More than 95% of patients with perianal abscesses that lead to fistula-in-ano are boys younger than 1 year. The second view is that perianal abscess and fistula-in-ano are two distinct entities. Perianal abscesses are seen in 22% of girls with fistula-in-ano, 68% of whom present after age 2 years.

Examination of the perineum may reveal an external opening of the fistula, with an outpouching of granulation tissue or purulent discharge. The fistula may appear as a perianal abscess. An internal opening may be felt as a nodule on the wall of the anal canal. The opening is invariably single. Probing the fistula should be done with the patient under anesthesia to avoid creating false passages.


Fistula-in-ano has commonly been divided into types according to the Parks classification[9]  (see the image below), as follows:

  • Superficial
  • Intersphincteric
  • Transsphincteric
  • Suprasphincteric
  • Extrasphincteric

In 2003, an American Gastroenterological Association technical review on perianal Crohn disease described another approach to classifying fistula-in-ano, whereby these lesions would be broadly categorized as either simple or complex.[10]  In this schema, a simple fistula is characterized as follows:

  • Lesser involvement of anal sphincters (superficial, intersphincteric, or low transsphincteric fistulas)
  • Only one opening
  • No association with an abscess or connection to an adjacent structure (eg, vagina or bladder)

The following are characteristics of a complex fistula:

  • Involvement of more of the anal sphincters (high transsphincteric, extrasphincteric, or suprasphincteric fistulas)
  • Multiple openings
  • Horseshoe configuration (crossing the midline anteriorly or posteriorly)
  • Association with a perianal abscess, connection to an adjacent structure, or both


Laboratory Studies

In cases of acquired fistula-in-ano due to infection, culture and sensitivity testing are indicated to identify the causative organisms.

Imaging Studies

Imageing studies that may be helpful include the following:

  • Endorectal ultrasonography (ERUS) and magnetic resonance imaging (MRI) [11] for mapping of complex fistulae; fistulography
  • Hydrogen peroxide–enhanced ultrasonography
  • Transperineal ultrasonography with a color Doppler study to visualize a perianal fistula or abscess and to evaluate its inflammatory activity in children with Crohn disease [12]


Approach Considerations

Surgery is required if pain is severe, if medical treatment fails, or if the fistula-in-ano recurs. About 95% of patients are completely cured, and 5% have a recurrence. Subsequent application of a kshara sutra is painless in 85% patients.

Associated severe medical conditions may contraindicate surgical procedures or anesthesia.

Medical Therapy

Medical therapy includes antibiotics and analgesics. In addition, treatment of the cause (eg, malignancy, Crohn disease or ulcerative colitis) is necessary. If underlying tuberculosis is detected, antitubercular treatment using rifampin, isoniazid, and ethambutol should be administered for 6 months.

Surgical Therapy

Asymptomatic fistulae require no treatment. Submucosal, intersphincteric, or low transsphincteric fistulae may be adequately treated by means of fistulectomy or fistulotomy.[13] Treatment varies according to the patient's sex and according to the type of fistula.


With the patient under anesthesia, the fistula tract is dissected from all sides by means of sharp dissection with scissors or diathermy from the external opening to the internal opening. The cavity left behind is allowed to heal by secondary intention.


With the patient under anesthesia, the fistula tract is probed. The probe is passed from the external opening and taken out from the internal opening. The whole fistula tract is then laid open over the probe. As with fistulectomy, the wound is allowed to heal by secondary intention.[14]

Radiowave fistulotomy

Radiowave fistulotomy offers benefits such as less postoperative pain, faster wound healing, and an early return to normal activity.[15] However, recurrence rates and continence problems are similar to those following conventional techniques.

Treatment of high anal fistula

A supralevator (pelvirectal) fistula may be secondary to local disease. If a traumatic fistula perforates the rectal ampulla, colostomy is usually needed.

Treatment of transsphincteric fistula

A transsphincteric fistula usually starts as an intersphincteric tract with a secondary tract in the ischiorectal fossa extending up to the levator axis. Treatment is directed toward the lower part of the tract, as healing of the upper tract may occur. If this does not take place, colostomy is required. A study by van Onkelen et al found that low transsphincteric fistulae could be treated successfully by ligation of the intersphincteric fistula tract without affecting fecal continence.[16]

Treatment of intersphincteric high anal fistula

This primarily starts as an abscess of the anal gland and extends upward and downward between the internal and external sphincters. Patients may have an opening into rectum above the anorectal ring. Treatment consists of laying open the tract by dividing only a small segment of the internal sphincter.

Use of seton, including medicated seton (kshara sutra)

A seton is a surgical thread often used to treat this condition. The seton can be silk, cotton, or any other suture material. It may be coated with medications.

A kshara sutra is a medicated thread often used in India to treat fistula-in-ano.[17, 18, 19, 20] To prepare this medicated type of seton, equal amounts of milk from the Euphorbianerifolia plant and powder of dry rhizomes from the Carcuma longa plant are thoroughly mixed. Cotton surgical threads (No. 20) are immersed in the mixture for 1-2 hours and then dried in hot air. This procedure is repeated often, sometimes as many as seven times.

Medicated setons are not commonly used in the rest of the world. Medications used in the kshara sutra are anti-infective and anti-inflammatory.

With the patient under anesthesia, the fistulous tract is probed to determine its extent and direction. A silver malleable probe is passed into fistula tract, and a suitable length of seton (kshara sutra) is cut and threaded over the eye of the probe. The kshara sutra is moderately tightened and is tied outside the anal verge over a piece of gauze.

A new piece of kshara sutra is replaced and tied every 6 days, using the railroad technique, until the last seton cuts through the fistula tract. The thread is shortened during each change, and the tract shortens. The wound heals by secondary intention.

The fistulous tract is cut as a result of the pressure the kshara sutra exerts on the anorectal tissue. The presence of the kshara sutra does not allow the cavity to close and facilitates continuous drainage of pus. Cutting and healing of the tract occurs simultaneously, and no pus pocket is retained. The chemicals applied to the thread are anti-inflammatory agents and have antibacterial properties. In addition, the alkaline pH of the kshara sutra prevents rectal pathogens from invading the cavity.

Video-assisted anal fistula treatment

Video-assisted anal fistula treatment (VAAFT), initially described in 2011 for use in adults with anal fistula, is being studied in children.[21] Pini Prato et al cited preliminary results indicating that VAAFT is feasible and safe in the pediatric population, as well as versatile.[22]  They found that older children and adolescents appeared to benefit most from the video-assisted approach.


Complications of fistula-in-ano include the following:

  • Recurrence
  • Delayed or impaired healing
  • Anal disease
  • Mucosal prolapse (which is not uncommon after fistula surgery)
  • Incontinence [23]

Long-Term Monitoring

Follow-up care involves antibiotic treatment, surgical dressing, and use of laxatives. A high-fiber diet is recommended.