The nerve branches to the external anal sphincter: the macroscopic supply and microscopic structure
SummaryThe study was performed using 45 pelvic half section specimens (41 fetal ones and four adults) The macroscopic dissection followed the nerve branches from their spinal roots up to the external anal sphincter. Three nerve branches were found: the anterior ramus arising from the external perineal nerve, the inferior rectal nerve and an independent posterior branch. The anterior and the inferior rectal nerve branches always emerged from the pudendal plexus. The posterior branch arising either from S4 or from the inferior rectal nerve was only found in (31% of our cases. Five anatomical distributions are described, percentages of every type notified. The fibre content of these nerve bundle branches was evaluated through histological sections using Heidenhain's azan stain and Luxol fast blue. The branches consisted of 2,896 to 2,137 fibres, 20% of them being unmyelinated and 80% containing various myelinated fibres. The nomenclature of these nerve branches has to be debated. The terms of anterior, middle and posterior anal nerves seem more suitable.ResumeL'etude porte sur 45 hemi bassins (41 de foetus et 4 d'adultes) dont les branches nerveuses sont dissequees depuis les racines spinales jusqu'au sphincter externe de l'anus. Elles sont disposees en 3 contingents: un contingent anterieur provenant du nerf perineal externe, un moyen le nerf rectal inferieur, un posterieur independant. Les contingents anterieur et moyen toujours constants proviennent du plexus honteux. Le posterieur, present dans 31% des cas provient de S4 ou du nerf rectal inferieur. Cinq dispositions anatomiques et leur frequence relative sont decrites. Le contenu fibrillaire des nerfs est analyse sur coupes histologiques colorees selon les techniques du bleu Azan de Heidenhain et du Luxol fast blue. Le nombre total de fibres varie de 2896 a 2137 fibres, avec 20% de fibres amyeliniques et 80% de fibres myelinisees de calibre variable. La nomenclature des branches sphincteriennes est discutee. Les termes de nerfs anaux anterieur moyen et posterieur semblent preferables.
Surgical and Radiologic Anatomy