Prenatal Ultrasound in the Diagnosis of Anorectal Malformations: Correlating Prenatal Signs With Postnatal Outcomes

Abstract

Objective: This study explored prenatal ultrasound markers in patients with anorectal malformations (ARMs).

Methods: All patients treated for ARM in our institution from January 2014 to December 2021 with an available expert fetal anomaly scan (eFAS) were reviewed. The eFAS images were assessed to evaluate the fetal anus, specifically by identifying hyperechoic anal mucosa surrounded by hypoechoic anal sphincter, referred to as "target sign" (TS). Furthermore, indirect signs of ARM were assessed and correlated with postnatal clinical symptoms.

Results: Of the 115 patients treated for ARM, 32 mothers underwent eFAS. TS was assessed in 22 fetuses, of which 17 (77.3%) had an absent or abnormal TS. Of the patients with a postnatally confirmed complex type of ARM, 90% had an absent or abnormal TS. One or more indirect signs of ARM were found in 16 out of 32 fetuses (50.0%), comprising echogenic bowel (n = 3), echogenic meconium (n = 2), dilated intestines (n = 7), echo-lucent cavity behind the urinary bladder (n = 4), abnormal external genitalia (n = 6), and polyhydramnios (n = 5).

Conclusion: This retrospective cohort study provides valuable insights into the potential role of TS assessment and indirect signs in the prenatal diagnosis of ARM. Future studies should further validate our findings and elicit whether TS assessment should be incorporated into prenatal screening protocols.

FIGURE 1

Normal, abnormal and absent target sign with corresponding postnatal image. Subscript: (A) Image of normal target sign. (B) Image of an abnormally shaped and anteriorly displaced target sign, along with the corresponding postnatal image of the missing anus in the expected position, but with a fistula that terminates in the vestibulum (rectovestibular fistula, blue arrow). (C) Image of absent target sign, along with the corresponding postnatal image of a cloacal malformation, where the urinary tract, vagina and rectum share one common tract (blue arrow).

FIGURE 2

Cohort selection flowchart. Subscript: ARM, anorectal malformation; eFAS, expert fetal anomaly scan; FAS, fetal anomaly scan.

FIGURE 3

Evaluation of the target sign on expert fetal anomaly scan and corresponding postnatal anorectal malformation type. Subscript: ARM, anorectal malformation; eFAS, expert fetal anomaly scan. ^† In these patients, there was no external fistula ending on clinical examination; therefore, it could be determined that it concerns a complex type of anorectal malformation. However, the specific type was not identified due to neonatal death.