Isolated Anorectal Malformation

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2021-01-23

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A wide spectrum of malformations involving the distal anus and rectum as well as the urinary and genital tracts, which can affect boys and girls.

Epidemiology

They occur in approximately 1 in 5000 live births.

Clinical description

Defects range from mild anal anomalies to complex cloacal malformations. They can therefore be classified into the following groups: imperforated anus without fistula, ARM with rectourinary or rectogenital fistula and complex ARM (cloaca). Associated anomalies include genitourinary defects (in approximately 50% of patients) and spinal anomalies. A cloaca is associated with a urological problem (such as obstructive uropathy) in 90% of babies and with hydrocolpos in 50%. Sacral anomalies (hemisacrum and sacral hemivertebrae) have been described; hemivertebrae may also affect the lumbar and thoracic spine, leading to scoliosis. A tethered spinal cord (in 25% of patients) may result in motor and sensory disturbances of the lower extremities. Syringomyelia and myelomeningocele can occur.

Etiology

The etiology remains unclear and is likely multifactorial. Familial cases have been described.

Diagnostic methods

The radiological evaluation of a newborn with imperforate anus should include an abdominal and pelvic ultrasound to evaluate for genitourinary defects as they need to be dealt with in the newborn period to avoid serious complications. Spinal ultrasound in the first three months of life and magnetic resonance imaging thereafter are useful radiological modalities for detecting spinal anomalies.

Differential diagnosis

ARM can occur in association with multisystem syndromes, such as Townes-Brocks syndrome, Currarino syndrome, Pallister-Hall syndrome, and Down syndrome (see these terms).

Genetic counseling

The risk of ARM for a sibling of a patient with ARM can reach 1%.

Management and treatment

Patients can either undergo a primary repair procedure (anoplasty) or a protective colostomy and definitive repair at a later date, depending on the malformation. The surgical approach to repairing these defects changed dramatically in 1980 with the introduction of the posterior sagittal approach, which allowed surgeons to view the anatomy of these defects clearly, to repair them under direct vision, and to learn about the complex anatomic arrangement between the rectum and genitourinary tract.

Prognosis

Early diagnosis, management of associated anomalies and efficient meticulous surgical repair can ensure a good functional outcome in terms of bowel and urinary control, and sexual function. However, fecal and urinary incontinence can occur due mainly to associated problems such as a poorly developed sacrum, deficient nerve supply, and spinal cord anomalies. For these patients, an effective bowel management program, including enema and dietary restrictions improves the quality of life.