Professor of Radiology, Paediatric Radiologist. Department of Radiology, Maastricht University Medical Center, Maastricht, The Netherlands
Anorectal malformations (ARM) include a wide spectrum of diseases that involve the distal rectum and anus lying in an abnormal position. At one end of the spectrum there is the anterior anus and at the other end there is sirenomelia and cloacal extrophy. The most used classification system was the Wingspread classification that distinguished between high, intermediate and low anomalies. High anomalies were anorectal agenesis with rectovaginal and rectoprostatic-urethral fistula and rectal atresia; intermediate malformations were rectovestibular, rectovaginal and rectobulbar-urethral fistula(figure); low-type malformations were classified as anovestibular and anocutaneous fistula as well as anal stenosis. The latest modification of these classifications systems is the Krickenbeck classification. This system comprises a classification system for anatomy, a classification system for operative procedures and a classification system for follow up. The incidence of imperforate anus in newborns is 1:4000-5000, most frequently with a rectourethral fistula in boys and a rectovestibular fistula in girls. The incidence of imperforate anus without fistula is reported at 5%. Rectoperineal fistula represents the simplest of all defects. The rectum opens in a small and stenotic orifice, located anterior to the centre of the sphincter. Rectovestibular fistula is the most common female defect, clinically evident as a normal external urethral opening and vagina, with a third hole in the vestibule represented by the rectum. Rectovaginal fistula is quite rare, occurring in <1% of cases, often misdiagnosed as vestibular fistula or cloaca.Rectal atresia or stenosis occurs in approximately 1% of all cases, and is the only entity in this spectrum with normal anal canal and sphincter mechanisms. ARM is frequently associated with sacral deformity, genitourinary malformations (also affecting the kidneys) and spinal cord abnormalities. High-type malformations generally show more severe associated abnormalities than low-type malformations. Persistent cloaca is the most severe type of ARM and seen exclusively in girls. It is a rare malformation with an incidence of 1:50000 and accounts for 10% of all ARM’s. The rectum, urethra and vagina fail to separate and drain via a single common channel onto the perineum. Other rare types of anorectal malformation syndromes are the Currarino triad, sirenomyelia and the spectrum of cloacal extrophy/OEIS complex.