Use of ultrasonography in determining the type of imperforate anus: a case series

Abstract

Preoperative differentiation between low type and high type imperforate anus (anorectal malformation, ARM) is very important to prevent the performing of inappropriate surgical procedures. Traditional invertogram is time dependent, difficult and may be harmful in neonates whose presentation is delayed and with abdominal distention. The present study assesses the diagnostic value of transperineal ultrasonography (T-PUS) in comparison with the invertogram, with the surgical diagnosis as the "gold standard", in a late-referred cohort. A prospective, interventional case series of consecutive neonates with imperforate anus seen at a tertiary referral center in the south of Iraq was performed. The typical referral was delayed (mean age >48 hours). A standard invertogram was performed (where clinically possible) and a T-PUS in the physiological supine position with a 7.5-12 MHz linear transducer for each patient. The P-P distance was recorded and the ARMs were categorized as low-type (<2.0 cm) or high-type (≥2.0 cm) ARMs. Diagnostic accuracy with respect to the intraoperative findings was the primary outcome. Secondary outcomes were feasibility and safety of each modality. Ten neonates (6 males, 4 females) were recruited. Mean age at presentation was 2.4±0.7 days (range: 1-3). In 40% (4/10) of patients, positioning the patient on the invertogram was impossible due to abdominal distension. Of the 6 patients who had both modalities, T-PUS correctly classified 10/10 (accuracy 100% (95% CI: 69.2%-100%)), while the invertogram did so in 4/6 cases (accuracy 66.7% (95% CI: 22.3%-95.7%)). In total, T-PUS was able to correctly identify 7 low-type (mean P-P distance 1.24±0.19 cm) and 3 high-type (mean P-P distance 2.63±0.15 cm) ARMs, with a 100% concordance with surgery. This difference between low and high groups was extremely significant (p<0.001, independent samples t-test). In 2 cases, the gas shadow was obscured by fluid-filled bowel loops making the invertogram unsuccessful. Transperineal ultrasonography is a safe, feasible and highly accurate tool for the diagnosis of imperforate anus, especially in cases presenting to the neonate late. This is better than the invertogram and allows for a correct and definitive surgical decision making. In all neonates with ARM we recommend that T-PUS is the primary, standalone imaging test and that the invertogram would be of no value in this setting.