Pre-operative MRI of anorectal anomalies in the newborn period.

Nine infants (six boys, three girls) with anorectal anomalies were examined in the immediate newborn period, prior to corrective surgery, with MRI. Three high, one intermediate and five low anomalies were found at MRI - one patient with a low lesion was subsequently found at surgery 2 months later to have a high anorectal anomaly. This infant had passed meconium per urethram soon after the MRI study, prompting the need for a protective colostomy and stressing the importance of a thorough clinical examination of babies with anorectal malformations. The MRI results and findings at surgery were in agreement in all other patients (n = 8). Hydronephrosis was evident in two and renal agenesis in one patient. Sacrococcygeal hypoplasia was found in two and two hemivertebrae in one infant. No spinal cord lesion was identified. One fistula was evident on MRI but four were later found at surgery. Uniformly hyperintense T 1 signal meconium was seen in all nine newborns, allowing for easy differentiation of rectal contents from rectal wall and the adjacent musculature. MRI can provide useful information regarding the development of the puborectal and external anal sphincter muscles, can help guide the pull-through procedure and help predict future continence pre-operatively in the newborn period.