Smooth muscle of the male pelvic floor: An anatomic study

Abstract

Introduction: Knowledge of the anatomy of the male pelvic floor is important to avoid damaging the pelvic floor muscles during surgery. We set out to explore the structure and innervation of the smooth muscle of the whole pelvic floor using male fetuses. Material and Methods: We removed en-bloc the entire pelvis of three male fetuses. The specimens were serially sectioned before being stained with Masson's trichrome and hematoxylin and eosin, and immunostained for smooth muscles, and somatic, adrenergic, sensory and nitrergic nerve fibers. Slides were digitized for 3D reconstruction. Accepted Article Results: We individualized a middle compartment that contains smooth muscle (SM) cells. This compartment is in close relation with the levator ani muscle (LAM), rectum, and urethra. We describe a posterior part of the middle compartment posterior to the rectal wall and an anterior part anterior to the rectal wall. The anterior part is split into 1) a centro-levator area of SM cells localized between the right and left LAM, 2) an endo-levator area that upholsters the internal aspect of the LAM, and 3) an infra-levator area below the LAM. All these areas are innervated by autonomic nerves coming from the inferior hypogastric plexus. The core and the infra-levator area receive the cavernous nerve and nerves supplying the urethra. Conclusion: We thus demonstrate that these muscular structures are smooth and under autonomic influence. These findings are relevant for the pelvic surgeon, and especially the urologist, during radical prostatectomy, abdominoperineal resection and intersphincteric resection.

The series of smooth muscle structures in the pelvic floors of men: Dynamic coordination of smooth and skeletal muscles

“…In the region anterior to the rectum and anal canal, the anterior bundle of longitudinal muscle (in addition to the rectourethral muscle) has been reported as a smooth muscle structure that descends in front of the external anal sphincter; however, it is not well known (Aigner et al, 2004; Muro et al, 2018; Nakajima et al, 2017; Zhai et al, 2011). In addition, it was classically common to call the skeletal muscle present in the deep perineal pouch the “deep transverse perineal muscle.” However, in recent reports, the smooth muscle plate‐like structures in the deep perineal pouch have often been described as the deep transverse perineal muscle (Muro et al, 2018; NyangohTimoh et al, 2019; Wu et al, 2017; Wu et al, 2018; Zhai et al, 2011). Thus, the smooth muscle structures around the rectum have been described separately in most previous studies, causing some confusion.…”

“…The levator ani is continuous with the external anal sphincter in the anterior and posterior regions of the anal canal, as illustrated in Figure 8. In addition, this series of smooth muscle structures appears to serve as a nerve pathway to the pelvic organs (NyangohTimoh et al, 2019). Analyzing nerves in relation to smooth muscles could clarify nerve distribution to the urethra and secretory glands.…”

“…Traditionally, the region anterior to the rectum and anal canal has been labeled “perineal body.” According to conventional understanding, this is a fibromuscular mass to which the perineal muscles are attached (Oh & Kark, 1973; Shafik, Sibai, Shafik, & Shafik, 2007; Standring, 2016; Stoker, 2009; Wu et al, 2015). However, recent studies have revealed that smooth muscle tissue extends into the region anterior to the rectum and anal canal (Kraima et al, 2016; Muro et al, 2018; Muro et al, 2019; Nakajima et al, 2017; NyangohTimoh et al, 2019; Okada et al, 2019; Uchimoto et al, 2007; Zhai, Liu, Li, Ma, & Yin, 2011). For example, the well‐known “rectourethral muscle” is composed of smooth muscles extending anteriorly from the longitudinal muscle of the rectum and connects the rectum and urethra.…”

“…For example, the well‐known “rectourethral muscle” is composed of smooth muscles extending anteriorly from the longitudinal muscle of the rectum and connects the rectum and urethra. In addition, several studies have reported on the “anterior bundle of the longitudinal muscle,” which consists of smooth muscle extending anteroinferiorly from the longitudinal muscle of the rectum and covers the anterosuperior surface of the external anal sphincter (Aigner et al, 2004; Muro et al, 2018; Nakajima et al, 2017; NyangohTimoh et al, 2019; Zhai et al, 2011). However, the spatial extent (three‐dimensional configuration) of the entire smooth muscle structure in this region and its detailed histological properties remain unclear.…”

The Five Diaphragms in Osteopathic Manipulative Medicine: Myofascial Relationships, Part 1

“…The gluteus maximus muscle is connected via a connective tissue strip at the level of the ischioanalis fossa to the muscle complex of the levator ani; a contraction of the latter is equivalent to a contraction of the gluteus maximus, as demonstrated by electromyographic and magnetic resonance assessments [13]. The innervation of the pelvic musculature is complex, as smooth muscle fibers (not just skeletal muscle fibers) can be found in the levator ani muscle group; these smooth fibers are found mainly in the central and medial area [14]. This area rich in smooth muscle fibers is innervated by the sympathetic nerves of the inferior hypogastric plexus; the remaining muscular area of the pelvic floor is innervated by the levator ani nerve and the pudendal nerve [15].…”