What is Anorectal Malformations (Imperforate Anus)?
Anorectal malformation, often referred to as imperforate anus, is a term for various conditions where the patient lacks a normal anal opening. Instead, they have a passage that opens onto the skin area around the genitals and anus or into nearby body structures. For males, this passage might be connected to the urinary system, and, for females, to the reproductive organs. The seriousness of the condition often depends on how far this passage opens from the normal location of the anal opening. The further away it is, the more likely there are other related problems like undeveloped muscles around the anus. Identifying the exact type of anorectal malformation is important because it can affect the patient’s long-term potential for controlling their bowel movements, which impacts their prognosis – or the likely course of their condition.
What Causes Anorectal Malformations (Imperforate Anus)?
Doctors aren’t exactly sure what causes anorectal malformations, but they believe that genetics might be involved. If you have a child with an anorectal malformation, there’s about a one percent chance that your next child will also have this condition. There are also certain genetic conditions linked to a higher chance of anorectal malformations. An example is the Currarino triad, a condition passed down through families, and trisomy 21, a condition where a person has an extra chromosome 21. As many as 95% of people with trisomy 21 have anorectal malformations without an abnormal connection, or fistula. This is compared to only 5% of all people with anorectal malformations.
Besides genetics, certain environmental factors may also play a role. These might include exposure to fertility treatments, certain medications, and having diabetes. Research studies using animals have found that exposure to substances like trans-retinoic acid and ethylene thiourea could lead to anorectal malformations.
Risk Factors and Frequency for Anorectal Malformations (Imperforate Anus)
Anorectal malformations, or abnormalities in the region of the anus and rectum, are fairly rare, affecting about 1 in 5000 babies born. They are slightly more common in boys than girls. Usually, about 70% of boys with this condition also have a connection between the rectal and urinary systems, known as a recto-urethral fistula. For girls, the most common anorectal malformation is a recto-vestibular fistula, a connection between the rectum and the vaginal area.
- Anorectal malformations are seen in about 1 in 5000 live births.
- These malformations are slightly more prevalent in males.
- About 70% of male patients with anorectal malformations have a recto-urethral fistula, meaning there’s a connection between the rectum and the urinary system.
- For female patients, the most frequently occurring anorectal malformation is a recto-vestibular fistula, which is a connection between the rectum and the vaginal area.
Signs and Symptoms of Anorectal Malformations (Imperforate Anus)
Newborns with malformations in the rectal and anal areas, known as anorectal malformations, often receive their diagnosis right after being born. Comprehensive newborn check-ups and further medical investigations are vital, as up to 60% of these babies may have other associated abnormalities.
As part of this comprehensive health check:
- The doctor will perform a perineal/anal exam – this is obligatory for all such cases.
- They will listen to the baby’s heart to determine if any murmur can be heard, indicating a possible heart condition.
- They will inspect the limbs for any signs of abnormalities.
- They will carry out a thorough genitourinary exam to check the baby’s reproductive and urinary systems.
A perfectly normal anus should be found in the right place and be the appropriate size for the baby’s age. The measurement for the anus of a full-term infant is typically 10 to 12 millimeters (as measured by a medical tool known as a Hegar dilator), while a 12-month-old baby’s anus should measure about 15 millimeters. Additionally, the anal opening should be centered within the anal muscle complex. However, it isn’t always possible to establish this match during casual clinic visits, and it might require an exam under anesthesia.
Furthermore, the doctor will examine the perineum (the area between the anus and the genitals), paying close attention to the development of the buttocks, the presence of a buttock crease, and whether there are any abnormal openings on the perineum. For female patients, the doctor will also perform a thorough vaginal examination, not only checking for any anomalies but also counting the number of openings on the perineum. These physical examination features can help provide insight into the specific type of anorectal malformation present.
Testing for Anorectal Malformations (Imperforate Anus)
For people diagnosed with an anorectal malformation, a variety of diagnostic tests are required. These malformations can stand alone but often don’t, so additional tests are needed. Around 60% of patients have another anomaly, and there’s a link between anorectal malformations and something called VACTERL defects. These are a group of birth defects that can affect the spine (vertebral), anus and rectum (anorectal), heart (cardiac), the passage that connects the throat to the stomach (tracheoesophageal), kidneys (renal) and limbs.
Because of this VACTERL association, every newborn diagnosed with an anorectal malformation should have specific imaging tests done. First, doctors insert a nasogastric or orogastric tube and take plain abdominal and chest films. These can show whether or not there’s a problem with the esophagus like esophageal atresia or a tracheoesophageal fistula, which are issues with the tube that connects the throat to the stomach. Spine x-rays are also needed to check for any problems with the vertebrae.
For baby boys, if there is no presence of a first stool on the skin around the anus without a clear fistula or abnormal connection after 24 hours of life, a specific x-ray, or invertogram, is necessary. Before this x-ray, the doctors put the baby face down with his bottom elevated for about 15 minutes. This allows any air in the digestive system to move to the very end of the rectum, helping in evaluating the most distant level of the bowel and determining the need for a colostomy, a procedure which allows stool to bypass part of the colon.
For baby girls with a single opening in the perineum, and diagnosed with a cloaca, a condition where the rectum, vagina, and urinary tract meet and fuse into a single common channel, an abdominal ultrasound is required. This screening checks for hydrocolpos, a condition where fluid fills and distends the vagina, and hydronephrosis, a condition that affects the kidneys. There’s also the need for an echocardiogram for all patients, a test that uses sound waves to produce images of the heart, to spot any congenital heart problems. A spinal ultrasound is also recommended to look for a tethered spinal cord. In addition, a sacral ratio derived from anteroposterior and lateral films will provide helpful information to families about possible challenges with bowel control as the child grows.
Treatment Options for Anorectal Malformations (Imperforate Anus)
In the case of patients with perineal fistulas or rectovestibular fistulas, surgery can typically be performed in the newborn period. However, factors such as the surgeon’s comfort level with the procedure and whether the patient has other health issues can affect the timing. For instance, if the patient has a heart defect, surgery may not be feasible. If surgery can’t be performed right away, the condition can also be managed temporarily by stretching the abnormal connection using a special tool called a Hegar dilator. This practise helps keep stool moving and avoids the baby’s abdomen becoming bloated.
For this temporary management, it’s crucial to ensure that stool continues to flow well and doesn’t lead to distention. If the condition is managed this way, surgery should be planned when the baby is around three months old. This approach helps fix the issue before the baby starts eating solid food, which could lead to constipation and distension. This particular type of surgery usually involves making a cut along the line between the buttocks and doesn’t require access to the abdomen.
For male babies with an abnormal connection between the rectum and the urinary tract or those diagnosed with cloaca (a condition where the rectum, vagina, and urinary tract meet and form a single common channel), a different route is usually taken. In these cases, a procedure is done in the newborn period to reroute stool to an opening (stoma) on the abdomen. This allows the baby to grow bigger before the definitive surgery. It also helps remove stool from the bowel section that’s connected to the urinary system. Before the main surgery, a special X-ray test can be performed to understand the exact type of abnormal connection, which helps plan the surgery.
Patients with conditions like cloaca, which require more complex management and life-long care, are usually referred to specialty centers. The timing for correcting these complex malformations can depend on several factors, including the specific type of malformation and associated additional health issues. Regardless of whether it’s a recto-bladder neck fistula or other high malformations, laparoscopy can be an important surgical strategy, especially when the abnormal connection is located high up in the body.
What else can Anorectal Malformations (Imperforate Anus) be?
While most babies with a medical condition known as anorectal malformation—where the anus and rectum don’t develop properly—are diagnosed right after birth, some might be diagnosed later. This is more common in children with conditions like anal stenosis or perineal fistulas, which might not be noticeable in newborns. In cases where an anorectal malformation is suspected but unclear, a specialized doctor called a pediatric surgeon can conduct an examination while the child is under anesthesia. This allows them to check whether the anus is the right size and in the right place.
In some rare instances, the child might have an anus that seems to be positioned further forward than what is typical. However, if its size is normal and it is at the center of the muscle complex, this variation would be considered normal.
What to expect with Anorectal Malformations (Imperforate Anus)
The future health outcomes for patients with an anorectal malformation, a condition affecting the rectum and anus, largely depend on their potential for long-term bowel control. Three key factors can give an idea of bowel control: the type of anorectal malformation, the ratio of the sacrum (a bone in the lower back), and the state of the spinal cord.
If the abnormal opening (fistula) is far from its usual location, the patient may have a lower chance of bowel control as they get older. A low sacral ratio could also suggest lower bowel control. Spinal conditions, such as a tethered cord, can also negatively impact bowel control.
However, even if these factors are present, a child can maintain cleanliness and social bowel control with the right care and a tailored bowel management program.
Possible Complications When Diagnosed with Anorectal Malformations (Imperforate Anus)
Complications during surgery can occur if attention is not given to staying within the correct tissue layers. This could potentially result in incorrect placement of the anus or its positioning outside the central area of the anal muscle complex. Extra caution is needed in male patients to avoid injury to urinary structures like the urethra, seminal vesicles, and vas deferens. In female patients, there’s a risk of damage to the vagina.
After surgery, some people may experience complications that range from skin level infections to deep wound infections. Issues might arise with the healing of the surgical join, a bulging out of the anal opening, or a narrowing of this opening. Recurring tunnels, or fistulas, may form between the urinary system in males or the reproductive system in females if the surgical repair is excessively tight or there is inadequate blood supply to the rectum. They can also occur as a result of surgical injury to anterior structures like the urethra or the vagina. At this point, it’s essential to ensure a healthy rectal wall, not the repaired structure, and a fat pad should be placed to support the repair.
The complications that could occur are:
- Incorrect placement of the anus
- Injury to urinary structures in males
- Damages to the vagina in females
- Skin level to deep wound infections
- Issues with surgical join healing
- Anal opening bulges
- Narrowing of the anal opening
- Recurring tunnels, or fistulas
- Surgical injury to the urethra or vagina
Preventing Anorectal Malformations (Imperforate Anus)
Educating parents about a child’s anorectal malformation primarily involves explaining the potential future issues their child may face related to bowel control. Three key factors can help predict these future bowel control issues: the type of anorectal malformation, the sacral ratio, and the condition of the spinal cord.
For the type of malformation, the farther the abnormality is from the regular position, the lower the chance of normal bowel control. The sacral ratio is another important factor. A normal sacral ratio is 0.9. If the sacral ratio is less than 0.4, this indicates a poor chance of proper bowel control.
Children with these malformations also need to be monitored for urinary tract infections. For girls, it is important to monitor the beginning of their menstrual cycle to make sure there is no blocked passageway in the female reproductive system. Lastly, spinal abnormalities like a tethered (stuck) spinal cord can also point to a lower chance of proper bowel control in the future.
