Internal anal sphincter nerves - a macroanatomical and microscopic description of the extrinsic autonomic nerve supply of the internal anal sphincter.

Background: The internal anal sphincter (IAS) contributes substantially to anorectal functions. While its autonomic nerve supply has been studied at the microscopic level, little information is available concerning the macroscopic topography of extrinsic nerve fibres. This study was designed to identify neural connections between the pelvic plexus and the IAS, provide a detailed topographical description, and give histological proof of autonomic nerve tissue. Methods: Macroscopic dissection of pelvic autonomic nerves was performed under magnification in seven (5 males, 2 females) hemipelvises obtained from body donors (67-92 years). Candidate structures were investigated by histological and…