An embryological study of fetal development of the rectourethralis muscle--does it really exist?

The so-called rectourethralis muscle is widely described in the urological literature. However, its description is subject to variations concerning extent and morphology. Moreover, little is known about its fetal development, which would allow a better understanding of the adult anatomy. The aim of this study was to investigate the morphology, extent and development of the rectourethralis muscle in fetal specimens.

A total of 15 normal human male fetuses were included in the study. Age ranged from 13th week of gestation to term. The histological study used plastination and standard and immunohistochemical techniques to identify the developing muscular structures in serial sections of the rectourethral space. Investigations in all 3 planes (coronal, sagittal and transverse) were performed.

In all sections of the proximal aspect of the rectourethral space no developing muscle fibers could be identified leaving the anterior wall of the rectum to join the rhabdosphincter or the apical prostate. In the distal aspect of the rectourethral space an independent muscular structure located between the external muscular layer of the anorectal canal and the dorsal bundles of the rhabdosphincter could be clearly demonstrated. This structure consisted of connective, smooth and striated muscle tissue, and was deeply anchored to the apical perineal body.

This study suggests that the so-called rectourethralis muscle is a misnomer in the urological literature. In the fetal period a developing muscular structure could be clearly identified as a part of the apical perineal body, which would correspond to the rectoperinealis muscle in the adult.