ABSTRACT
<p><b>OBJECTIVE</b>To explore the regional anatomy of the rectum including the perirectal fasciae and spaces.</p><p><b>METHODS</b>Twenty-one cadavers (15 males and 6 females) were embalmed and their vessels were visualized by injection with color dye. From the cadavers, 30 hemipelvis and 6 three-quarter pelvis were harvested. The perirectal fasciae and spaces and the pelvic autonomic nerves were dissected and examined.</p><p><b>RESULTS</b>Three tissue layers were dissected from the inside to the periphery including the proper rectal fascia enveloping the mesorectum, the presacral fascia, and the piriformis fascia fused with the sacral periosteum. The mesorectum comprised 2 parts with the classical posterolateral fat covered by the proper rectal fascia posteriorly and the anterior fat covered by the posterior layer of Denonvilliers fascia anteriorly. 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 retrocolic space, anterior to the space between the 2 layers of Denonvilliers fascia(prerectal space).</p><p><b>CONCLUSIONS</b>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 total mesorectal excision.</p>