A new concept of the anatomy of the anal sphincter mechanism and the physiology of defecation. X. Anorectal sinus and band: anatomic nature and surgical significance.

A study, comprising dissection and microscopic examination of the pectinate area with special consideration to anal glands, was performed in 29 cadavers varying from fully mature neonatal deaths to 52 years of age. At the junction of the anal canal proper with the rectal neck, an "anorectal sinus" (a submucosal anal circumferential depression) was identified in 18 specimens; in 6 specimens, the anorectal sinus was replaced by a fibroepithelial band ("anorectal band"); in 5 specimens, the anorectal sinus was absent, and in 3 of the 5 specimens only scattered epithelial cells ("epithelial debris" of the anorectal sinus) were detected. These findings suggest that the anorectal sinus is an embryonic vestige which results from hindgut "invagination" by the proctodeum. Its persistence or partial obliteration would result in the formation of tubular structures which are considered by investigators as anal glands. The sinus may be completely obliterated or may leave behind a submucosal "anorectal band" or scattered "epithelial debris." Evidence in favor of this new concept is put forward. The role of anorectal sinus, anorectal band, and epithelial debris in the genesis of some idiopathic anal lesions is discussed.