Anorectal malformation

Anorectal malformation, classically known as atresia ani or imperforate anus, is a congenital malformation (present from birth) affecting the digestive tract in its final section, the rectum and the anus. These patients are typically born without an anal orifice or with a malformed anus which ends in the form of a small fistula in the perineum.

Between 50-60% of children with anorectal malformation (ARM) will also present other anomalies affecting the urological system (the most frequent), gynecological, heart, spinal cord and sometimes the esophagus and upper and lower limbs.

There are several types of anorectal malformation, among which the following stand out:

• In boys and girls: perineal fistula, MAR without fistula, anal stenosis, rectal atresia, cloacal exstrophy (MAR, bladder exstrophy and omphalocele).
• Only in children: recto urethral fistula (bulbar and prostatic) and rectovesical fistula.
• Only in girls: rectovestibular fistula, rectovaginal fistula, cloacal malformation.

Symptoms of anorectal malformation

The main symptom in newborns with MAR is the absence of meconium expulsion at birth. Meconium is the first stool passed by a newborn shortly after birth. In patients with a small fistula there may be partial expulsion of meconium.

In both cases, this results in intestinal obstruction requiring surgical treatment in the first hours of life in most cases. Newborns may present vomiting, refusal to feed or abdominal distention due to the accumulation of feces and gas in the intestine.

The incidence of MAR is 1 in 5000 live newborns and its cause is multifactorial. It is believed that for the development of an anorectal malformation there must be a combination of genetic and environmental factors.

Chromosomal abnormalities have been identified in 5-10% of patients with anorectal malformation on up to 17 different chromosomes. This suggests that multiple genes are involved in the development of the anorectal region. There are a number of congenital syndromes that have MAR as one of their clinical components. These include Down syndrome (trisomy 21), Currarino syndrome (MAR, sacral defect and presacral mass), Townes-Brocks syndrome (MAR and auditory and renal anomalies) and VACTERL association, among others.

Diagnosis of anorectal malformation

Only 15% of anorectal formations (ARF) are diagnosed prenatally during pregnancy and the vast majority of them are complex: rectovesical fistula in the male and cloaca in the female. This is because these malformations have the most associated anomalies and these anomalies (usually renal and cardiac anomalies) are identifiable in utero.) Only 3% of isolated MAR (without associated malformations) are diagnosed prenatally.

The vast majority of children are diagnosed in the first hours of life. The diagnosis of MAR is mainly clinical, after a detailed physical examination that varies greatly from patient to patient depending on sex and type of malformation.

In all patients with MAR, several complementary examinations should be performed in the first 24 hours of life, before making a surgical decision. The purpose of these tests is to determine whether there are other associated diseases that may affect medical management and surgical treatment. It is important that the diagnosis is made by pediatric surgeons with experience in this type of malformation to avoid diagnostic errors that can lead to erroneous treatment with consequences for future continence.

Diagnostic tests for anorectal malformation (ARM) include:

1. Chest X-ray: to rule out rib and vertebral anomalies and esophageal atresia.
2. Abdominal X-ray: to rule out the diagnosis of duodenal atresia and as in the previous case is useful to identify anomalies of the thoracic and lumbar spine.
3. AP and lateral sacral radiography: to rule out sacral anomalies and to be able to calculate the Sacral Index, which helps us to establish a future prognosis of continence.
4. Spinal ultrasound: to rule out abnormalities of the spinal cord.
5. Abdominal ultrasound: to rule out renal and excretory tract abnormalities.
6. Echocardiogram: To rule out cardiac abnormalities.

Treatment of anorectal malformation

Regardless of the type of malformation, 100% of patients require an evaluation by a pediatric surgeon who will establish the indicated surgical treatment according to the physical examination and general condition of the patient.

The most frequently performed treatments are:

1. Colostomy: A stoma (artificial opening) is made to temporarily bypass the colon to the abdominal wall so that the patient can evacuate until the time of definitive reconstruction.
2. Anoplasty: Definitive repair in these patients is scheduled between 4-6 months of age. The most commonly used surgical technique is the posterior sagittal anorectoplasty. In this procedure, a midline approach (incision) is made between both buttocks to identify the muscular complex (the sphincter) and place the "new anus" in the center of the anus to maximize the possibility of continence.

Once the patient has recovered from the operation and the anoplasty has healed adequately, the colostomy will be closed about 2-3 months after the anorectomy.

Occasionally (not in all cases) it may be necessary to dilate the anoplasty performed by the parents at home until the colostomy is closed. This is done to prevent narrowing of the newly reconstructed anus due to the physiologic healing process.

3. Primary anoplasty: this type of intervention is reserved for minor or low malformations that allow a definitive repair in the neonatal period without the need for colostomy.

Follow-up and prognosis

All patients with anorectal malformation need long-term follow-up as they may develop constipation or fecal incontinence from an early age:

Constipation in these patients may manifest, paradoxically, with multiple small bowel movements, known as encopresis or overflow incontinence.

It requires an "aggressive" treatment with laxativesto avoid future complications due to the dilation and accumulation of stool in the rectal ampulla causing what we know as "megarectum". The most commonly used laxatives are usually stimulants to promote colon motility along with fibers that increase stool volume and consistency.

Fecal incontinence in MAR is present in patients with "high" malformations, such as rectovesical fistula or long channel cloacae, or in patients with medullary malformations, such as an anchored medulla. This incontinence can be treated either with bowel transit slowing agents or with retrograde (rectal) or antegrade (appendicostomy) enemas.

There are several developmental milestones that are very important in the follow-up of patients with MAR. These are the age close to sphincter control, which is later in children with MAR between 2 and 5 years of age, and adolescence.

Due to the wide variety of MAR types and associated anomalies, these patients should be evaluated by pediatric surgeons and urologists who specialize in this type of disease so that treatment is appropriate and the impact on quality of life is minimized.