Perirectal fascia and spaces: annular distribution pattern around the mesorectum

In view of debate on the optimal surgical planes for total mesorectal excision, this study was designed to explore the regional anatomy of the perirectal fascia and spaces.

Twenty-one cadavers (15 male and 6 female) were embalmed and their vessels visualized by injection with color dye. From the cadavers, 30 hemipelves and 6 three-quarter pelves were harvested. The perirectal fascia and spaces and the pelvic autonomic nerves were dissected and examined.

Three tissue layers were dissected from the inside to the periphery: the proper rectal fascia enveloping the mesorectum, the presacral fascia, and the piriformis fascia fused with the sacral periosteum. The mesorectum comprised 2 parts: posterior, with the classical posterolateral fat covered by the proper rectal fascia; and anterior, with the anterior fat covered by the posterior layer of Denonvilliers fascia. Extending anteriorly to the anterior layer of Denonvilliers fascia, the presacral fascia bisected the space between the mesorectum and the piriformis fascia into the retrorectal space and the presacral space. The retrorectal space extended cranially to the left Toldt's space, anterior to the space between the 2 layers of Denonvilliers fascia.

From the inside to the periphery, the proper rectal fascia, the presacral fascia, and the muscular fascia are distributed in an annular pattern around the mesorectum. The presacral fascia divides the perirectal space into 2 annular parts: the central retrorectal space and the peripheral presacral space. The retrorectal space is the ideal surgical plane for the total mesorectal excision.