Spatial distribution of smooth muscle tissue in the male pelvic floor with special reference to the lateral extent of the rectourethralis muscle: Application to prostatectomy and proctectomy

Abstract

The anatomy of the rectourethralis muscle is essential for performing radical prostatectomy and proctectomy. The rectourethralis muscle is known to continue to the rectal wall posteriorly and to the membranous urethra anteriorly. However, the lateral extent of the rectourethralis muscle remains unclear. This study aimed to verify the hypothesis that the rectourethralis muscle laterally extends and directly adheres to the levator ani. Eight male cadavers were used for macroscopic dissection, and three male cadavers were used for immunohistological analysis using anti-smooth muscle and anti-skeletal muscle antibodies. The rectourethralis muscle laterally extended smooth muscle fibers both superoposteriorly and inferoanteriorly toward the levator ani. The smooth muscle fibers sandwiched the levator ani superoanteriorly and inferoanteriorly. A few smooth muscle fibers of the rectourethralis muscle inserted into the levator ani. This study clarified the spatial distribution of the rectourethralis muscle and its detailed positional relationship with the levator ani. The findings are valuable especially to urologists and anorectal surgeons for dissecting an optimal layer around the urethra and the rectum, and for avoiding rectal or urethral injuries during surgery. Clin. Anat., 2018. © 2018 Wiley Periodicals, Inc.

Anatomy of the smooth muscle structure in the female anorectal anterior wall: convergence and anterior extension of the internal anal sphincter and longitudinal muscle

“…The anterior extension of the smooth muscle of the anorectal canal has been confirmed in males. The smooth muscle structure anteriorly, extending to the posterior urethra, is termed the rectourethralis muscle, whereas the smooth muscle structure extending antero‐inferiorly to cover the anterior surface of the external anal sphincter was reported as the anterior bundle of the longitudinal muscle . The anterior extension structure of the internal anal sphincter and rectal longitudinal muscle described in our study (indicated by the star in Figs b, c and d, h) is considered to be the structure homologous to the rectourethralis muscle of males, on the basis of the location, morphology and tissue composition.…”

“…Additionally, researchers who clarified the anatomical planes for an extralevator abdominoperineal excision have for a long time realized that the interface between the anterior anorectal wall and the structures of the posterior genitourinary complex have many similarities in males and females, including a fibromuscular point (perineal body) that serves as a connecting point in the middle of the non‐bony pelvis . The perineal body refers to the fibromuscular tissue in the region between the rectum and urogenital structures . Larson et al .…”

“…The muscle layer of the anorectal anterior wall in males is particularly complex. One of the complicating factors is the anterior extension of the smooth muscle layer, and it is known that several fibres of the longitudinal muscle extend anteriorly to form the rectourethralis muscle in males .…”

Interactive three‐dimensional teaching models of the female and male pelvic floor

“…Only smooth muscles allow that degree of stretching without injury (Seow and Solway, ). Accordingly, several studies have confirmed its status as a smooth muscle (Nakajima et al, ; Muro et al, , ). The developmental anatomy of the rectourethral muscle and perineal body can account for much of the controversies that surround the deep perineal muscle (Table ).…”

“…Although the perineal body is an acknowledged item in “Anatomical Terminology” (A09.5.00.0005 (Terminol, )), it is not universally accepted as a specific structure. Thus, Akita and colleagues argue that description of the perineal body as a node is a too delimited description and should, instead, be considered a region (Muro et al, ). However, our description of the perineal body as a fibromuscular structure in the wedge‐shaped space between the lower portion of the rectum and the vagina or urethra (“region”) that penetrates with many antenna‐like extensions between the fibers of the rectourethral muscle (“shape”) (Wu et al, ; Wu et al, ; Wu et al, ) is not very different from the impression that emanates from their trichrome‐stained illustrations of the rectourethral muscle (Muro et al, ).…”