Prenatal ultrasonography has a low sensitivity and specificity for the detection of ARM. A normal anus is visualized as a circular rim of hypoechogenicity in the perineum together with a central linear echogenic stripe. The absence of this circular rim is described as imperforate anus on the prenatal scan. Enterolithia-sis has been described on prenatal scans of rectovesi-cal or rectourethral fistula in patients with ARM . Harris retrospectively viewed prenatal scans of children with ARM and demonstrated dilated colon on prenatal ultrasonograms . Oligohydramnios and a highly distended vagina are signs of imperforate anus on ultrasound. However, due to the frequency of concurrent anomalies associated with ARM it is these other lesions that are usually diagnosed on the prenatal scan. Polyhydramnios associated with an upper gastrointestinal obstruction, sacral anomalies, and vertebral and renal defects are much more read ily seen on ultrasonography than an imperforate anus. At birth, a history of excess oral secretions and central cyanosis implies the potential presence of VACTERL (Vertebral, Anorectal, Cardiac, Tracheo-Esophageal, Renal and Limbs particularly radial) anomalies.
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