Anorectal malformation is a spectrum of congenital defects of the distal bowel, mostly diagnosed at birth.
To describe the prenatal imaging findings of anorectal malformations, explore the causes of the low rates of prenatal diagnosis, compare the accuracy of prenatal ultrasound (US) and magnetic resonnance imaging [MRI] and evaluate the relevance of information obtained at MRI.
Children treated for anorectal malformation at our hospital and with available prenatal studies were retrospectively identified and included in the study. We reviewed prenatal imaging exams, listed findings suggestive of the diagnosis, and compared results with the final classification.
Fourteen fetuses and neonates - eight with intermediate-high type anorectal malformation and six with cloacae - fulfilled the inclusion criteria. All had associated congenital anomalies. Prenatal exams included 13 US and 8 MRI exams, with 7 children having both exams. Suggestive findings for anorectal malformation were detected in 50% of the cases prenatally and in 85% upon review. They were prospectively detected in 31% and 50% of the cases at US and MRI and retrospectively in 62% and 100% at US and MRI, respectively. MRI was superior to US because it improved the diagnosis, especially in cloacae, and provided relevant additional information that changed management in two cases.
The most important signs suggesting anorectal malformation are an absent target sign and anomalous distal bowel wall and rectal fluid. Complementary prenatal MRI improves the diagnosis of anorectal malformation.