Anatomical observation and clinical significance of rectosacral fascia in total mesorectal resection

Objective: To observe the anatomical architecture of rectosacral fascia and discuss the best plan for accurate peri-rectal dissection in laparoscopic/robotic total mesorectal resection (TME). Methods: A descriptive cohort study was carried out. A total of 127 patients with rectal cancer who underwent TME in the Department of Colorectal Surgery at the affiliated Union hospital of Fujian Medical University were included, patients' demographics with their pathological details and operation videos were collected for analysis. Another 20 high-definition images of post-TME surgical specimens were collected from our digital database. A total of 28 cadaveric models were examined at the Laboratory of Clinical Applied Anatomy, Fujian Medical University, to observe the anatomical details of rectosacral fascia. Results: (1) Anatomical observation showed that the pre-hypogastric fascia attaches to the proper fascia of the mesorectum in a horizontal arc posteriorly, forming the rectosacral fascia. If this fusion couldn't be identified and appropriately transected during posterior space dissection, it would be easy to destroy the proper fascia and dissect through the mesorectum resulting in residual mesorectum tissue. After the fascia transaction, the proper fascia of the mesorectum is still intact distally. The upper part of rectosacral fascia bilaterally re-separated again into the proper fascia and pre-hypogastric fascia. The pre-hypogastric fascia acts as a "fascia barrier" when dissecting the lateral space constantly from posterior to anterior. The right attachment of the rectosacral fascia was gradually transected. The pelvic plexus from the right S2-S4 was covered by the pre-hypogastric fascia which is considered the outer side layer of rectosacral fascia laterally. It was observed that the fascia continued with the anterior layer of the Denonvilliers' fascia, which has been transected during anterior space dissection. The proper fascia, which is the inner side layer of rectosacral fascia laterally, was still intact. The edge of the right rectosacral fascia attachment ran obliquely from the back and upward into the front direction. The left extension was similar to the right. (2) Cadaveric specimens: at the level of the lower edge of S4 vertebral body, the pre-hypogastric fascia fused with the proper fascia to form the rectosacral fascia. The right attachment margin of the rectosacral fascia was cut off step by step. The attachment margin of the rectosacral fascia went from the back and upward to the front downward direction. The right edge of rectosacral fascia attachment continued with the anterior layer of the Denonvilliers' fascia at the pre-rectal space and attached to the pre-hypogastric fascia laterally. The pelvic plexus sends out many tiny rectal branches on the anterolateral side, which pass through the transitional area between pre-hypogastric fascia and the anterior layer of the Denonvilliers' fascia to innervate the rectum. (3) TME specimens observation: the posterior attachment of rectosacral fascia was curved around the mesorectum with bilateral oblique attachments. The mesorectum was covered by fusion fascia below the posterior and bilateral attachment margin while it was covered only by the proper fascia above it. Conclusion: according to the morphological characteristics of rectosacral fascia, the rectosacral fascia should be dissected at the level of S4 vertebral body posterior to the rectum in an arc, shape and then enter the superior-levator space. Before dissecting the bilateral spaces, the anterior space of the rectum should be dissected first. The anterior layer of the Denonvilliers' fascia should be cut off into an inverted "U" shape, and then the lateral space should be dissected from anterior to posterior. Finally, the lateral attachment of rectosacral fascia was transected to ensure the integrity of the mesorectum without damaging the pelvic plexus branches and NVB.