Prenatal Ultrasound Evaluation for Detection of Imperforate Anus with Fistula

Abstract Objective This study aims to observe the prenatal ultrasound image characteristics of imperforate anus with fistula and explore the application of prenatal ultrasound in diagnosing this condition.Methods A retrospective review was conducted on six cases diagnosed with imperforate anus with fistula using prenatal ultrasound. Fetal pelvis examination, through sagittal or coronal views, was performed to identify the location of the fistulas. The results were compared with induction of labor autopsy or physical examination of the newborn.Results Prenatal ultrasound successfully diagnosed six cases of imperforate anus with fistula, including four cases of low-type (two rectovestibular fistula and two rectoperineal fistula) and two cases of high-type (rectovaginal fistula). In the four cases of low-type, a distinctive "target ring sign" was observed in the transverse view of the perineum. The fistulas were superficially located, and their distal openings, or even the entire fistula, could be identified in either the sagittal or coronal plane. In the two cases of high-type, no "target ring sign" was observed, and the fistulas were deeper within the skin. However, a portion of the middle segment of the fistula was detectable in the sagittal or coronal plane.Conclusions Prenatal ultrasound imaging, under normal fetal position and amniotic fluid conditions, can visualize fistulas in fetuses with imperforate anus. The sagittal and coronal views obtained through the sacrococcygeal region provide optimal visualization of the fistulas. The diagnosis of low-type imperforate anus may be challenging due to the presence of the "target ring sign." Further scanning of the fistula in the sagittal or coronal plane can help reduce missed diagnoses of low-type imperforate anus. The identification of fistulas also offers new insights and directions for the prenatal diagnosis of low-type imperforate anus.