Anorectal malformations are birth defects of a child’s anus or rectum that interfere with the normal passage of stool. When the anus is completely blocked, the condition is called imperforate anus.

In children with anorectal malformations, the anus may be missing, blocked by a thin or thick layer of tissue, or more narrow than normal. In rare cases, the anus may be normal while the rectum is blocked or narrowed.

Many children with anorectal malformations have a fistula, or abnormal passage, between the rectum to another part of the body, such as the

• perineum, the skin between the anus and the sex organs
• urethra or bladder
• the vagina

In some children with anorectal malformations, the rectum and the urinary tract have the same opening. This abnormality is called a cloaca.

Imperforate anus is a birth defect where the opening to the anus is missing or blocked. The anus, also known as the rectum, is the opening at the end of the intestines through which stool (bowel movement) leaves the body. Imperforate anus may end in a pouch, be too narrow (stenotic or atresic), or open into part of the urinary system, female or male reproductive system, or other system of body. Symptoms may include absence of the first stool within 24 to 48 hours after birth, no anal opening, anal opening in an abnormal place, stool coming out from the vagina, base of penis, scrotum, or urethra, and/or swollen belly.

Although the exact cause of imperforate anus is not fully understood, it is believed to be due to the abnormal development of the rectum when the embryo is forming inside the womb. Many forms of imperforate anus occur with other birth defects. Imperforate anus may also be part of a syndrome with multiple birth defects.

Treatment may include colostomy and surgery to correct the defect. Prognosis depends on the severity and type of imperforate anus and the severity and type of any other birth defects.

The lower gastrointestinal (GI) tract is the last part of the digestive tract. The lower GI tract consists of the large intestine and the anus.

The large intestine absorbs water and changes the waste products of the digestive process from liquid into formed stool. The large intestine includes

• the appendix, a finger-shaped pouch attached to the cecum
• the cecum, the first part of the large intestine, which is connected to the end of the small intestine
• the colon, which has four sections: the ascending colon, the transverse colon, the descending colon, and the sigmoid colon
• the rectum, the lower end of the large intestine leading to the anus

The anus is a 1-inch opening at the end of your digestive tract through which stool leaves your body. The anus includes the sphincter muscles—muscles that open and close and allow you to control bowel movements.

About 1 in every 5,000 babies is born with anorectal malformations.

When examining a newborn baby, doctors may find signs of anorectal malformations, such as

• no visible anus
• an anal opening that is not in the normal location
• an anus that is tighter or more narrow than normal

In the first 24 hours after birth, babies with anorectal malformations may pass no stool or may pass stool through a fistula and out of the perineum, urethra, or vagina.

Babies with signs of anorectal malformation need medical treatment right away to prevent complications.

Anorectal malformations occur when the anus and rectum don’t develop normally before birth. Experts don’t know what causes problems with the development of the anus and rectum. However, genes or changes in genes—called mutations—may play a role.

Boys are slightly more likely than girls to be born with anorectal malformations.

If parents have one child with an anorectal malformation, the chance that a future child will have the condition is 1 in 100, which is higher than the average risk of 1 in 5,000.

Children with anorectal malformations may have birth defects that affect other parts of the body. These may include defects of the

• urinary tract and sex organs
• heart
• spine
• gastrointestinal (GI) tract
• trachea, also called the windpipe
• kidneys
• arms and legs

In some cases, children with Down syndrome also have anorectal malformations.

If anorectal malformations are not diagnosed and treated shortly after a baby is born, the baby may develop symptoms of intestinal obstruction, such as vomiting, bloating or visible swelling of the abdomen, and not being able to pass stool. Intestinal obstruction can lead to serious complications, such as a hole in the wall of the intestine called a perforation, serious infection, and sepsis.

After anorectal malformations have been treated with surgery, some people may have complications later in life such as

• constipation
• bowel control problems
• bladder control problems
• problems with sexual function

Doctors diagnose anorectal malformations with a physical exam and imaging tests. They may also order tests to check for other health problems that are common in children with anorectal malformations.

Physical exam

Shortly after a baby is born, a doctor will examine the baby from head to toe. Doctors often diagnose anorectal malformations during this exam. Doctors will also examine the baby’s perineum and genitals and check for other birth defects.

Imaging tests

Doctors may use the following tests to examine defects of the anus and rectum

• ultrasound, which uses sound waves to create an image of organs
• x-rays, which use a small amount of radiation to create pictures of the inside of the body
• magnetic resonance imaging (MRI), which takes pictures of the body’s internal organs and soft tissues without using x-rays

Doctors treat anorectal malformations with surgery. The type of surgery depends on the location and type of malformation.

Doctors often perform surgery in the first few days after the baby is born. In some cases, doctors can repair the anorectal malformation with one operation. In other cases, doctors first perform a colostomy to attach the colon to a stoma, an opening in the abdomen that allows stool to exit the body. Then doctors repair the anorectal malformation with one or more operations when the baby is older.

Doctors may recommend regular follow-up care and additional treatments for any complications that develop after surgery or later in life.