High-type anal atresia presenting as a pseudo "target sign" on prenatal ultrasound

We present prenatal ultrasound images of two high anal atresia cases. The main screening tool used in our clinic is the "target sign" in the tangential view of the fetal perineum. In the current report, we discuss some challenges in the existing screening practices.

CASE 1: A 28-year-old woman (gravida 1, para 0) with a twin pregnancy underwent ultrasound screening at 21 weeks of gestation when an absent "target sign" in twin A was discovered. At the same time, we were able to present evidence that if the wrong plane was visualized, other structures could be mistaken as the "target sign". Eventually, high-type anal atresia was confirmed postnatally in Twin A. CASE 2: A 29-year-old woman (gravida 1, para 0) came to our clinic for routine screening at 23 weeks of gestation. In the standard tangential view at the level of the perineum, a low-high concentric circle structure resembling a "target sign" was visualized during a prenatal scan. However, anal atresia was discovered postnatally. A retrospective review of prenatal images revealed discrepancies from the typical "target sign".

High-type anal atresia may present as a pseudo "target sign" on prenatal ultrasound. Visualization of a "target sign" on fetal ultrasound does not always exclude the diagnosis of anal atresia. It is crucial to evaluate the size, shape, level, and position of the "target sign". The appearance of the bilateral hyperechoic perianal tissue is a hint for the screening of anal atresia.