What Is an Imperforate Anus?

A Congential Birth Defect

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An imperforate anus, also known as an anorectal malformation (ARM), involves the lack of an anal opening, or the lack of the proper size or abnormal location of the anal opening, which is present at birth (congenital).

Imperforate anus is considered a very rare congenital condition. According to a 2018 study, “anorectal malformations (ARMs) occur in approximately 1 out of every 5,000 births and are slightly more common in males.”

The condition often involves an abnormal fistula (tunnel) that connects the rectum or the colon to the vagina or the bladder. It requires surgical correction to repair the abnormality. Common synonyms (in addition to the term ARM) that you may see that are interchangeable with the term imperforate anus include:

  • Anal atresia
  • Anal membrane
  • Anal stenosis
  • Ectopic anus
  • High imperforate anus
  • Low imperforate anus
  • Perineal anus
imperforate anus
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Types of Imperforate Anus

Anorectal malformation (ARM) is an umbrella term that describes a group of birth defects involving the anal/rectal area. To get an idea of exactly what and where this defect is, it may help to understand the function of the rectum and the anus as it pertains to digestion.

After food travels through the colon (large intestine), it moves into the rectum, and finally to the anus for elimination of the waste products (also called stool or feces). To reach the anus, the solid waste must move through the rectum (which connects to the very last segment of the colon).

When a baby is born with an anorectal malformation (ARM), the anus does not form properly in utero (before birth).

There are two primary categories and several types of imperforate anus, categorized by the location of the defect. The two primary types of defects include:

  • High imperforate anus: The rectum ends above the puborectalis sling (a band of muscle fibers that is part of the pubococcygeus, one such muscle, the pubococcygeus (PC), supports the bladder and rectum and helps control urine flow.
  • Low imperforate anus: The rectum traverses (extends across) the puborectalis sling.

There are several different types of defects that involve the anus or rectum that are considered a type of anorectal malformation (ARM). Because the genital anatomy differs between males and females, the type of imperforate anus defect may differ by sex as well.

A fistula is an abnormal connection between two hollow spaces. Common fistulas which are considered types of imperforate anus defects (AMRS) include the following.

ARM With Perineal Fistula

This type of defect causes the rectum to end in the perineum (the area between the anus and the scrotum in a male and the anus and vulva in a female). The rectum is narrowed, and the abnormal anal opening is located outside of the sphincter muscles (the muscles responsible for controlling bowel movements).

When this abnormal opening is located outside the sphincter muscle complex, there are usually very few voluntary sphincter muscles surrounding it. This type of imperforate anus can occur in males or females.

ARM With Recto-Bulbar Fistula

This defect involves the malformation of the rectum so that in males the rectum abnormally connects to the urethra (the tubular structure that carries urine from the bladder through the penis and outside of the body). A recto-bulbar fistula results in urine mixing with feces and emptying into the urethra in males.

Females with a recto-bulbar fistula have a defect in the anus, which does not form correctly, and the rectum ends in a structure called the vestibule. The vestibule is a small area between the labia (exterior genitals) and the vaginal opening.

ARM With Recto-Prostatic Fistula

In males, this is a type of defect that results in an abnormal connection between the rectum and the urethra at the level of the prostate. This type of ARM results in feces and urine mixing and emptying into the urethra.

ARM With Recto-Bladder Neck Fistula

In this condition, an abnormal connection between the rectum and the bladder which results in feces emptying into the urethra. This is one of the least common types of ARMS seen in males.

ARM Without a Fistula

This type of defect results in a blind pouch which is an abnormal ending of the rectum (without connecting to the anus). In an ARM without a fistula, the rectum forms a pouch that does not connect to any other structure. This type of defect can occur in males or females. 

ARM With Recto-Vaginal Fistula

In females, this type of defect involves an abnormal passageway between the rectum and vagina; this results in feces leaking into the vagina. It is a very uncommon type of ARM.


This is another type of ARM that occurs in females. It’s a very complicated type of birth defect that involves the anus, vagina, and urethra joining into one passageway, all exiting the body through one opening instead of having three openings comprised of an opening each for the urethra, vagina and rectum

Because each type of defect is different anatomically, each one may result in a different level of severity of symptoms and each has a different prognosis. 

Imperforate Anus Symptoms

The symptoms of imperforate anus differ depending on the type of defect the baby is born with. Common symptoms in general include:

  • No stool passed during the first day or two after birth
  • Stool that is passed through the wrong opening (such as the urethra or vagina)
  • Distention (swelling of the abdomen)
  • A missing anal opening (or an anal opening that is in the wrong place)
  • A missing or misplaced anus
  • Incontinence (unable to hold urine or feces)
  • Infections in areas where the misplaced opening allows feces to travel where it should not go, such as in the urethra

Imperforate anus may be linked to a malformation syndrome, characterized by a spectrum of birth defects. According to a 2018 study, nearly 64% of infants diagnosed with an ARM were found to have one or more additional anal anomalies (malformations) and only 36% had just one type of ARM and no other birth defects.

One example of this is called VACTERL association, which is a very rare disorder with several defects, including:

  • An anal defect
  • A skeletal defect
  • A kidney defect
  • A heart defect
  • Other congenital malformations


Imperforate anus is a congenital defect that may be inherited. It is thought that an imperforate anus may be linked with an autosomal dominant (only one copy of a mutated gene is necessary), autosomal recessive (both copies of a mutated gene—one from each parent—are present) or X-linked recessive inheritance.

An X-linked recessive inheritance occurs most often in males and is caused by mutations in genes on the X chromosome. According to a 2018 study, the condition may occur in response to mutations in one or more genes which could possibly be linked with specific environmental factors (such as maternal drug use during pregnancy).


Many anorectal malformations are diagnosed at birth during the newborn’s initial examination. The anus may not be in the correct place or it may not be present at all. Other times, a prenatal ultrasound may detect the malformation in a fetus before birth.

When congenital malformations (birth defects) are diagnosed before birth, the healthcare provider may refer the mother and unborn baby to a maternal-fetal medicine center, specially equipped to care for babies who need intensive care at birth.

Common diagnostic tests which can assist in providing an overview of the type and location of the ARM include:

  • Abdominal X-rays
  • Renal ultrasound to detect associated abnormalities of the urinary tract
  • Pelvic ultrasound
  • Spinal ultrasound to rule out any problems in the spinal cord that may be associated with similar symptoms of ARM, such as urinary or fecal incontinence
  • Magnetic resonance imaging (MRI) to view specific anatomical areas involved
  • Echocardiogram to check for associated heart defects that could be present such as when the infant has a syndrome, like VACTERL association


The treatment of anorectal malformation/imperforate anus is different depending on which type of malformation the child has. In most instances, surgical intervention to correct the defect is required. The surgical procedure is called a posterior sagittal anorectoplasty (PSARP). The surgery may occur shortly after birth

 Other treatment modalities may be required if there are any associated conditions. The care team will create a unique treatment plan, depending on the exact type of ARM your child has and based on any other malformations that may be present.

Posterior Sagittal Anorectoplasty (PSARP)

The procedure to repair an imperforate anus involves moving the anal opening to the correct location (within the anal sphincter, or muscles that control the anus).

A laparoscopic (a procedure involving small incisions and a thin scope with a camera) or robotic-assisted surgical technique (the use of very small surgical tools attached to robotic arms) is used whenever possible to reduce the amount of blood loss, lessen the pain and promote faster healing than a tradition or open method (involving a large incision) of surgery.

Colostomy Surgery

It’s possible that before a PSARP can be performed, a child may need a colostomy A colostomy is a procedure to create an opening in the abdominal wall for a means of allowing feces and gas to leave the body until corrective surgery can be performed.

After the PSARP is performed, the colostomy opening will be closed (usually within a few months of the corrective surgery), giving the new surgical site a chance to heal, before the colostomy is closed up.

With a simple ARM (or those which are less complex) most children can maintain normal bowel control after the surgical repair is complete without undergoing a bowel control program.

Bowel Control Program

When a child has a complex type of ARM, part of the overall treatment plan will be to initiate a bowel program to help the child overcome any problems with constipation or incontinence.

A bowel control program is comprised of a multidisciplinary team of healthcare providers such as:

  • A urologist
  • A gastroenterologist
  • A physical medicine and rehabilitation specialist (sometimes called a physiatrist)
  • A colorectal surgeon
  • A nutritionist
  • A psychologist or other mental health professional

 Treatment modalities that may be part of a bowel control program include:

  • Diagnostic testing
  • Nutrition consultation and counseling
  • Behavioral (mental health) counseling
  • Coordination of medical care as well as surgical management
  • Pelvic floor rehabilitation (to help build up the pelvic floor muscles necessary for normal elimination).

What to Expect After Surgery

 One of the biggest concerns for a parent who is anticipating any type of surgery for their child is the worry about how much pain the child will have to endure. A child recovering from a PSARP is said to experience only very minimal pain.

As a parent, you will be allowed to hold your child after surgery, offering comfort and emotional support. The care team will provide close observation to observe for signs or symptoms of infection. 

Often, the child will have frequent loose bowel movements which can result in skin breakdown in the diaper area. Within a few weeks after surgery, the frequency of bowel movements will slow down, and the stool will gradually become firmer.

Some children will continue to have constipation after surgery. The healthcare provider may order a high fiber diet and laxatives. A postoperative visit will be scheduled for a few weeks after the surgery so the surgeon can check on your child’s progress.


It’s important to note that toilet training for a child who has undergone treatment (surgery) for an imperforate anus should be started at the same time as those who have not had any defects.

In many instances, children who are born with an ARM may take longer to gain bowel control than other children. This depends somewhat on the type of malformation the child was born with.

It’s important to discuss toilet training with your child’s care team and get input from the experts as far as the type of specific potty training methods to employ and what to expect.

If your child is not potty trained by the time most children are (around the age of 3 to 4), you may want to consult with a local bowel management program, such as the one at Cincinnati Children’s Hospital (called the Colorectal Center at Cincinnati Children’s).

The program utilizes many different tools (such as the use of laxatives, a special diet and more) to help kids with corrective surgery from an ARM get bowel control.

A Word From Verywell

Some types of imperforate anus are considered minor and relatively easy to treat, with very good long-term prognosis. Other types are complex, involving multiple structures and bodily functions (such as impacting the urinary system and having an impact on bowel and bladder control as well as sexual function.

Take an active role in advocating for your child with the healthcare team so you learn more about your child's specific needs and treatment options.

6 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. National Organization for Rare Disorders. (NORD). Imperforate anus.

  3. Cinncinnati Children's. Anorectal malformations/imperforate anus.

  4. Cedars Sinai. Perineal fistula.

  5. Zwink N, Jenetzky E. Maternal drug use and the risk of anorectal malformations: systematic review and meta-analysis. Orphanet J Rare Dis. 2018;13,75. doi:10.1186/s13023-018-0789-3

  6. Michigan Medicine. Michigan Bowel Control Program.

By Sherry Christiansen
Sherry Christiansen is a medical writer with a healthcare background. She has worked in the hospital setting and collaborated on Alzheimer's research.