Prenatal Ultrasound Diagnosis of Fetal Imperforate Anus: Fallacies in Diagnosis

ABSTRACT Background To summarize prenatal sonographic characteristics of imperforate anus, investigate contributing factors for diagnostic errors, and explore strategies to improve diagnostic precision for imperforate anus. Methods A retrospective analysis was conducted on 19 pregnant women with missed or misdiagnosed imperforate anus (involving 20 fetuses). Summarize the prenatal ultrasound characteristics of these missed and misdiagnosed cases, compare the results of prenatal ultrasound and postpartum diagnosis, analyze the main reasons and technical bottlenecks for missed and misdiagnosed cases, and explore strategies to improve the diagnostic accuracy of fetal imperforate anus. Results Among the 13 missed cases of imperforate anus, all (100%, 13/13) exhibited a pseudo “target sign” on the perineal transverse view during the missed diagnosis. None of these cases underwent detailed perineal sagittal and coronal scanning during the initial ultrasound. Among the seven misdiagnosed cases, three cases (42.86%, 3/7) showed an unclear “target sign” without sagittal and coronal planes evaluation. Two cases (28.57%, 2/7) displayed a pseudo “target sign,” while the remaining two cases (28.57%, 2/7) showed a clear “target sign.” In these seven cases, sagittal views in four cases revealed interrupted mucosal hyperechoic lines, later attributed to compression by fetal buttock fat (three cases) or a perianal mass (one case). Among the 13 fetuses with imperforate anus, there were a total of 10 cases of low type, two cases of high type, and one case of intermediate type. Conclusion Although prenatal diagnosis of imperforate anus is challenging, it is feasible. Standardized scanning and distinguishing between true and pseudo “target sign” are crucial. Additionally, multi‐section continuous scanning of the anus is helpful to display the overall appearance of the anal canal and improve diagnostic accuracy.