Background: Diagnosis of imperforate anus using transperineal ultrasonography, pouch-perineum distance less than 10 mm has been defined as the cut-off for low type imperforate anus which can be safely treated with immediate anoplasty. While the distance greater than 15 mm has been defined for intermediate and high type imperforate anus, diverted colostomy is still required.

Objective: To compare the accuracy of transperineal ultrasonography to prone lateral cross-table radiography in order to define the type of imperforate anus.

Materials and Methods: Subjects are five neonates with imperforate anus admitted from April 2016 to January 2018. The distance between distal rectal pouch and perineum (P-P distance) was measured with both transperineal ultrasonography and prone lateral cross-table radiography. The transperineal ultrasonographic findings were compared with prone lateral cross-table radiographic and surgical findings.

Results: The mean distance between distal rectal pouch and perineum (P-P distance) in the 5 imperforate anus neonates measured with transperineal ultrasonography, prone lateral cross-table and operative findings were 1.12+0.6 (SD) mm, 1.95+0.85 mm (SD) and 1.20+0.27 (SD) mm, respectively. The P-P distances in transperineal ultrasonography were observed to be more closed to those of precise operative measurement. All patients were classified as low type imperforate anus and underwent immediate anoplasty.

Conclusion: Transperineal ultrasonography is a non-invasive imaging technique that can accurately define the type of imperforate anus. Ultimately, all 5 patients underwent immediate anoplasty with accurate diagnosis.

Keywords: Transperineal ultrasonography (US), Imperforate anus (IA), Pouch-perineum (P-P) distance, Prone lateral cross-table radiography