[Distribution pattern of the rectal circumferential fascia and its clinical significance: An anatomical study].

Objective: To investigate the pattern of distribution of the circumferential fascia of the rectum and elucidate its clinical implications. Methods: In this descriptive study, we examined the gross anatomy of four male hemipelvic cadaveric specimens from the Department of Anatomy at Fujian Medical University and the histological features of 16 fresh postoperative specimens from patients who had undergone total mesorectal excision for rectal cancer at the Department of Colorectal Surgery, Union Hospital, Fujian Medical University, between January and December 2022. The resultant combination of gross anatomical and histological features was employed to assess the following areas: (1)the morphology of the anterior mesorectum and fascia at the peritoneal reflection; (2)the caudal attachment point of Denonvilliers' fascia; (3) the fusion area of the pelvic plexus and the pre-hypogastric fascia; (4)the lateral and posterior attachment edges of the rectosacral fascia; and (5) selected histological features. Results: Our findings were as follows. (1) At the peritoneal reflection, the anterior mesorectum forms a triangular fat pad with a dense fascial structure. The base of this pad extends anteriorly across the most caudal point of the peritoneal reflection, with Denonvilliers' fascia originating from the anterior side of the triangle, near the bladder side of the peritoneum craniad to the peritoneal reflection. (2) The caudal attachment of Denonvilliers' fascia is at the angle between the seminal vesicles, the ampulla of the vas deferens, and the prostate. It adheres tightly to the prostatic capsule and vascular bundles pass through its cephalic side. (3) The pre-hypogastric fascia transitions laterally to merge with Denonvilliers' fascia; its middle part being inseparable from the main body of the pelvic plexus, which gives rise to the nerves that innervate the rectum. (4) The rectosacral fascia is formed by fusion of the fascia propria with the pre-hypogastric fascia. The resultant fused fascia bifurcates into two leaves on the right side; the outer leaf being the pre-hypogastric fascia and the inner leaf the fascia propria. (5) Histologically, the peritoneal reflection zone shows cuboidal epithelium of the peritoneum at its lowest point with no detectable origin of Denonvilliers' fascia. The anterior side of the peritoneal reflection, from which Denonvilliers' fascia originates, has a dense double-layered fascial structure comprising thick collagen fiber (16/16). The fascia propria exhibits a thinner and looser collagen fiber structure and its origin varies between individuals, 13/16 originating together with Denonvilliers' fascia from the craniad side of the peritoneal reflection, and 3/16 originating separately from the most caudal point of the peritoneal reflection. The caudal edge of Denonvilliers' fascia has a double-layered fascial structure with multiple S100-stained areas. The posterior edge of the rectosacral fascia has a fused fascial structure, thick nerve fibers being clearly observable between collagen fibers originating from the pre-hypogastric fascia under high magnification. The lateral edge of the rectosacral fascia extends interiorly, maintains the integrity of the fascia propria. Conclusions: In this study, we investigated the pattern of distribution of the circumferential fascia of the rectum by cadaveric dissection and histological examination of postoperative specimens. We found that the anterior mesorectum forms a triangular fat pad that can serve as a reference for dissection anterior to Denonvilliers' fascia, by making incisions 1 cm above the peritoneal reflection. The region of fusion of Denonvilliers' fascia with the prostatic capsule on the caudal side is rich in neurovascular bundles, contradicting the traditional view of a retroprostatic plane. This finding supports the practice of cutting Denonvilliers' fascia 0.5 cm above the base of the seminal vesicles. The fusion of the fascia propria with the pre-hypogastric fascia posteriorly forms the rectosacral fascia, which bifurcates into two leaves on both sides of the rectum, the inner leaf being the fascia propria and the outer leaf the pre-hypogastric fascia. These transition anteriorly to become Denonvilliers' fascia and fuse densely with the main body of the pelvic plexus on both sides. These findings provide a theoretical foundation for protecting the pelvic plexus and hypogastric nerve by transecting Denonvilliers' fascia and then dissecting in a top-to-bottom direction (i.e., from anterior to caudal), ultimately leading to the transection of the pre-hypogastric fascia.