Anatomical reevaluation of the anococcygeal ligament and its surgical relevance

BACKGROUND: With the development and spread of surgical procedures for total mesorectal excision and intersphincteric resection, rectal surgeons have gained frequent opportunities to observe connective tissues around the anal canal. However, uncertainty remains as to the exact identity and location of these structures. OBJECTIVE: The aim of this study was therefore to identify and describe the morphology of connective tissue structures extending between the coccyx and anal canal. DESIGN AND SETTING: This was a descriptive study carried out at university facilities for anatomic research. The study comprised histologic evaluation of paraffinembedded tissue specimens from preserved cadavers of 20 elderly adults and examination of frozen pelves from 6 fresh cadavers. MAIN OUTCOME MEASURES: From each cadaver, we obtained a tissue mass containing the dorsal wall of the distal rectum and anal canal, the coccyx, and the covering skin. Most sections were stained with Masson-Trichrome solution for collagen and smooth muscle fibers. RESULTS: Dissection of fresh cadaver demonstrated the anococcygeal ligament extending from the coccyx to the anal canal between bilateral slings of the levator ani. Histologic examination showed that the anococcygeal ligament was divided into a ventral and a dorsal layer and contained abundant smooth muscles, elastic fibers, and small vessels. The ventral layer extended from the presacral fascia to the conjoint longitudinal layer of the anal canal. The dorsal layer was recognized as a bundle extending between the coccyx and external anal sphincter. The dorsal layer was much thicker along and near the midsagittal plane than the lateral areas. The levator ani was located independently of and dorsal to the anococcygeal ligament. LIMITATIONS: This study used cadavers from elderly donors; thus, the specimens might have had age-related degeneration. CONCLUSIONS: The anococcygeal ligament is divided into 2 layers: a thick ventral layer, rich in thin vessels and extending from the presacral fascia to the conjoint longitudinal layer of the anal canal, and a thin dorsal layer extending between the coccyx and external anal sphincter. The anococcygeal ligament is one of the critical structures for decision-making regarding rectal and upper anal canal mobilization.