3-Dimensional Demonstration of Fetal Anal Canal and Sphincter

Abstract

Purpose: To identify the fetal anal canal and sphincter using 3-dimensional (3 D) ultrasound.

Materials and Methods: 3 D volumes of the fetal pelvis were acquired prospectively in 52 fetuses between 10 and 39 gestational weeks. A standard method for evaluating the fetal anal canal and sphincter was developed. Measurements of mucosal and muscular circumferences and the length of the anal canal were taken.

Results: The anal canal was demonstrated in 46 out of 50 patients (92 %). The sonographic characteristics of the anal canal in the axial plane appear like a “target sign” with an echogenic mucosa in the center, the hypoechoic internal sphincter muscle surrounding it and an outer echogenic circle reflecting the external sphincter. Measurements of mucosal and internal sphincter circumferences and the length of the anal canal demonstrated linear growth during pregnancy (p < 0.01). One case of anal atresia was demonstrated.

Conclusion: The fetal anal canal can be visualized when a systematic analysis is performed using a 3 D volume dataset.

Zusammenfassung

Ziel: Der Nachweis des fetalen Analkanals und des Schließmuskels mittels dreidimensionaler (3-D-) Sonografie.

Material und Methoden: 3-D Volumina des fetalen Beckens wurden prospektiv bei 52 Feten zwischen 10 und 39 Schwangerschaftswochen aufgenommen. Eine Standardmethode für die Beurteilung des fetalen Analkanals und Schließmuskels wurde entwickelt. Die Umfänge von Mukosa und Muskeln wurden bestimmt und die Länge des Analkanals vermessen.

Ergebnisse: Der Analkanal konnte bei 46 von 50 Patienten dargestellt werden (92 %). Das sonografische Charakteristikum des Analkanals erscheint in der axialen Ebene als Zielscheiben-Zeichen mit der echoreichen Mukosa im Zentrum, dem umgebenden echoarmen M. sphincter ani internus und einem äußeren Ring, der dem M.sphinter ani externus entspricht. Messungen der Umfänge von Mukosa und M. sphincter ani internus sowie der Länge des Analkanals zeigten ein lineares Wachstum im Schwangerschaftsverlauf (p < 0,01). Ein Fall einer Analatresie wurde nachgewiesen.

Schlussfolgerung: Der fetale Analkanal kann mittels systematischer Analyse eines 3-D-Volumen-Datensatzes dargestellt werden.

Key words

3 D ultrasound - anus - obstetrics

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