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KEY POINTS
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Key Points

  • Incidence is 1 in 5,000 livebirths. Has been linked to maternal diabetes, thalidomide, ethanol, and assisted reproductive technology.

  • Imperforate anus is difficult to diagnose by prenatal sonographic studies.

  • Sonographic findings that may be due to imperforate anus include transient bowel dilation in first trimester, intraluminal calcifications in the colon, and persistent distal bowel dilation later in gestation.

  • Fetal MRI may be an important adjunct to ultrasound examination if anorectal malformation is suspected.

  • 50% of anorectal malformations have associated anomalies of the spine, limbs, genitourinary system, trachea, esophagus and the heart. Echocardiogram is indicated.

  • Associated with many syndromes and chromosome abnormalities. Amniocentesis is indicated for fetal karyotype.

  • Delivery should occur in a tertiary care center with pediatric surgical, radiologic, and genetic expertise available.

  • Bowel continence is usually achieved in 90% of patients.

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CONDITION
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Imperforate anus has been recognized since antiquity, but has only been treatable in all of its forms in the latter half of the past century. The first surgical anoplasty for a low-type of imperforate anus was performed by Amussat in Paris in 1835. The next significant advance did not occur until the work of Stephens, who described a combined sacral and abdominal perineal approach based on cadaveric dissections. This highlighted the importance of the puborectolia sling (Stephens, 1953). The modern approach to reconstruction of imperforate anus was pioneered by deVries and Pena in 1982, with the posterior sagittal approach to the whole spectrum of anorectal malformations using the posterior sagittal anorectoplasty (PSARP) (deVries and Pena, 1982; Pena and deVries, 1982).

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Anomalies of the anus and rectum have usually been explained on the basis of an arrest of the caudal descent of the urorectal septum toward the cloacal membrane between 4 and 8 weeks of gestation (Fitzgerald and Fitzgerald, 1994). At 4 to 6 weeks the cloacal membrane becomes partitioned into the anterior urogenital sinus and the posterior anorectum by the cranial to caudal growth of mesoderm-derived urorectal septum. The urorectal septum fuses with the cloacal membrane at what then becomes the perineal body (Paidas and Pena, 1996). The mesoderm-derived urorectal septum is composed of the midline Tournex fold and two lateral Rathke folds. The lower third of the anal canal is derived from the ectoderm of the anal pit. Fusion of the hindgut mesoderm with the ectoderm occurs at the dentate line. Failure of Rathke folds to develop results in arrest of the inferior urorectal septum, resulting in a rectourethral fistula in the male and a persistent cloaca in the female. This arrest in Rathke folds usually occurs just below the paramesonephric duct, but a more caudal arrest in Rathke folds could result in a high rectovaginal fistula in a female. Failure of both Rathke and Tourneaux folds in males results in rectovesicular fistulas at the bladder neck. In the female it is more likely to result ...

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