Comparison of Diagnostic Accuracy for the Low-Type Imperforate Anus Between Prone Cross-Table Radiography and Sonography.

OBJECTIVES: To compare the diagnostic accuracy for the low-type imperforate anus between prone cross-table radiography and sonography.

METHODS: We included 20 neonates with imperforate anus: 13 with a surgically proven low type and 7 with an intermediate or high type. The distance between the distal rectal pouch and the perineum (pouch-perineum distance) was measured by both sonography and prone cross-table radiography. A previously established pouch-perineum distance of 10 mm was used as the cutoff for diagnosis of a low-type imperforate anus. The fistula location was also determined with sonography. We then compared the diagnostic accuracy of the imaging methods for a low-type imperforate anus using the cutoff value of the pouch-perineum distance alone and both the cutoff value of the pouch-perineum distance and fistula location. The McNemar test was used for statistical analysis.

RESULTS: With the use of only the pouch-perineum distance, the diagnostic accuracy for the low-type imperforate anus based on sonographic measurements was comparable with the accuracy achieved by prone cross-table radiographic measurements (60.0% [12 of 20] versus 45.0% [9 of 20]; P = .625). With the use of the pouch-perineum distance and fistula location, the diagnostic accuracy of sonography was significantly better than the accuracy of prone cross-table radiography (90.0% [18 of 20] versus 45% [9 of 20]; P = .012).

CONCLUSIONS: The diagnostic accuracy of sonography for the low-type imperforate anus based on both the pouch-perineum distance and fistula location is better than that of prone cross-table radiography. If the pouch-perineum distance on prone cross-table radiography is greater than 10 mm, a sonographic examination to determine the fistula location could be recommended.