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Transperineal Sonography for Determination of Type of Imperforate Anus

June 26, 2009
Written by: , Filed in: Pediatric Radiology
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A recent study which was conducted to assess whether transperineal sonography is valid and accurate in discriminating different types of imperforate anus in neonates has proved useful in introducing a simple value for separating the high and intermediate type of imperforate anus from the low type, and in diagnosing imperforate anus more accurately.

The Study
Over a 10-year period, infants were examined with transperineal ultrasound after clinically being diagnosed with imperforate anus.

Methodology
On ultrasound, the distal rectal pouch was identified and its distance to the perineum was recorded.

Thereafter, the distance and the type of imperforate anus were confirmed on the basis of surgical findings.

The type of imperforate anus is classified as high, intermediate, or low, depending on the relation of the distal rectum to the puborectalis sling of the levator ani muscle.

High type is defined as a rectum that terminates above the level of the puborectalis.

Intermediate type terminates within the puborectalis.

Low type passes through the levator ani muscle group and through the central puborectalis, terminating below the sling.

Pediatric Diagnostic Imaging

The Society for Pediatric Radiology
Pediatric Diagnostic Imaging program features the advances and diversity of pediatric imaging by reviewing state-of-the-art clinical material and advanced cutting-edge research presentations. This program presents a group of international experts who discuss state-of-the art diagnostic imaging and the outlook for the future direction of the specialty.
Read more or order:  Pediatric Diagnostic Imaging

Results
54 patients were included in the study. A final diagnosis of imperforate anus was made for 22 patients.

The mean distance between the distal rectal pouch and the perineum in this group was 10.4 mm. For intermediate imperforate anus, 17 patients were identified. They had a mean pouch-to-perineum distance of 23.6 mm.

For the patients identified as a high imperforate anus, of which there were 17 patients, the mean pouch-to-perineum distance was 25.5 mm.

Conclusions
As can be seen from the results, there was considerable overlap for the pouch-to-perineum distance for those patients diagnosed with intermediate or high imperforate anus. After thorough statistical analysis, the cutoff value for the distance from the distal rectal pouch to the perineum was determined to be 15 mm. This cutoff value yielded a sensitivity estimated to be 100% and a specificity of 86% when diagnosing low imperforate anus. This cutoff value correctly diagnosed 19 of the 22 infants with low imperforate anus, with the remaining 3 infants diagnosed on the findings of anocutaneous fistula. All 34 cases of intermediate or high imperforate anus were correctly classified at sonographic examination using this cutoff value, with no reliable value for separating those diagnosed with high imperforate anus from those with indeterminate type.

Reviewer’s Comments
The study introduces a simple value for separating the high and intermediate type of imperforate anus from the low type.

The authors only briefly touch on the importance of taking into account the presence and type of fistula on clinical grounds, which also aids in diagnosis.

This proved valuable with the 3 infants diagnosed with low imperforate anus based on an anocutaneous fistula–something to keep in mind when putting this data into practice.

Author: Basil Hubbi, MD).

Reference:

Haber, Hans P., Seitz, Guido, et al. Transperineal Sonography for Determination of the Type of Imperforate Anus. AJR 2007; 189:1525-1529

Pediatric Diagnostic Imaging

The Society for Pediatric Radiology
Pediatric Diagnostic Imaging program features the advances and diversity of pediatric imaging by reviewing state-of-the-art clinical material and advanced cutting-edge research presentations. This program presents a group of international experts who discuss state-of-the art diagnostic imaging and the outlook for the future direction of the specialty.
Read more or order:  Pediatric Diagnostic Imaging
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