In anal atresia (also known as imperforate anus), the tissue closing the anus may be several centimeters thick or just a thin membrane of skin. Association with other anomalies is common. Diagnosis is by physical examination. Treatment is with primary surgical repair or with temporary colostomy followed by deferred repair.
(See also Overview of Congenital Gastrointestinal Anomalies.)
The incidence of anal atresia is approximately 1 in 3000 to 5000 live births (1–3). This anomaly is frequently associated with other congenital anomalies (half or more of cases) such as VACTERL (vertebral anomalies, anal atresia, cardiac malformations, tracheoesophageal fistula, esophageal atresia, renal anomalies and radial aplasia, and limb anomalies) (2, 3).
In simple cases of anal atresia, the anal canal ends blindly at the anal membrane, which forms a diaphragm between the endodermal and ectodermal portions of the anal canal. In more severe cases, a thick layer of connective tissue may be found between the terminal end of the rectum and the surface because of either a failure of the anal pit to develop or atresia of the ampullar part of the rectum (rectal atresia) (2).
In high (supralevator) lesions (in which the atresia ends above the levator ani muscles of the pelvic floor), a fistula often extends from the anal pouch to the perineum or the urethra in males and to the vagina, the fourchette, or, rarely, the bladder in females. Cutaneous fistulas are usually present in low (infralevator) lesions.
Anal atresia is part of a spectrum of anorectal malformations that also includes anal or rectal stenosis, anteriorly placed anus, fistulae, and a cloaca.
General references
1. Ford K, Peppa M, Zylbersztejn A, Curry JI, Gilbert R. Birth prevalence of anorectal malformations in England and 5-year survival: a national birth cohort study. Arch Dis Child. 2022;107(8):758-766. doi:10.1136/archdischild-2021-323474
2. de Blaauw I, Stenström P, Yamataka A, et al. Anorectal malformations. Nat Rev Dis Primers. 2024;10(1):88. Published 2024 Nov 21. doi:10.1038/s41572-024-00574-2
3. Ambartsumyan L. Medical management of anorectal malformations. Aliment Pharmacol Ther. 2024;60 Suppl 1:S77-S84. doi:10.1111/apt.17897
Diagnosis of Anal Atresia
Physical examination
Prenatal ultrasound diagnosis of anorectal malformations, including anal atresia, is possible but not common (1).
Anal atresia should be obvious on comprehensive physical examination of the neonate because the anus is not patent. If the diagnosis of anal atresia is missed and the neonate is fed, signs of distal bowel obstruction soon develop.
The urine should be examined for meconium, indicating the presence of a fistula to the urinary tract. Plain radiographs and fistulograms with the neonate in a lateral prone position can define the level of the lesion. Ultrasound is also helpful for classifying the type of lesion and for assessing any other associated anomalies. A cutaneous fistula generally indicates low atresia. If no perineal fistula exists, a high lesion is likely.
Diagnosis reference
1. de Blaauw I, Stenström P, Yamataka A, et al. Anorectal malformations. Nat Rev Dis Primers. 2024;10(1):88. Published 2024 Nov 21. doi:10.1038/s41572-024-00574-2
Treatment of Anal Atresia
Primary perineal repair or temporary colostomy followed by deferred repair
Before surgery, neonates with anal atresia should be evaluated for other congenital anomalies.
The decision to perform a primary perineal repair or to perform a temporary colostomy followed by deferred repair depends on the gender of the infant, the presence and location of a fistula, the location of the rectal pouch (high versus low lesion), the development of perineal structures, and the experience of the surgeon. Neonates with a cutaneous fistula and a low lesion can undergo primary perineal repair. Several malformations may be repaired as a single-step procedure (1).
Long-term postoperative care is focused on managing both constipation and incontinence. Care can include attention to toilet training, medications (eg, stool softeners, laxatives, fiber supplementation), and enema techniques (2).
Treatment references
1. Hartford L, Brisighelli G, Gabler T, et al. Single-stage procedures for anorectal malformations: A systematic review and meta-analysis. J Pediatr Surg. 2022;57(9):75-84. doi:10.1016/j.jpedsurg.2021.12.024
2. Ambartsumyan L. Medical management of anorectal malformations. Aliment Pharmacol Ther. 2024;60 Suppl 1:S77-S84. doi:10.1111/apt.17897
