Prostate stroma itself is immediately surrounded by a thin covering of tissue named as "capsule", which was absent at the anterior surface of prostate [2, 13]. Some researchers found that the "prostatic capsule" shifted to or showed a smooth transition to the anterior fibromuscular stroma [14, 15]. Our successive celloidin slices revealed that the bilateral ends of the capsule were attached to AFMS (Fig. 1a and b). 3-D reconstruction demostrated that the capsule and AFMS together formed a pocket like structure to accommodate the prostate and the urethra (Fig. 4c).
Recently, the prevailing view about the anatomy of the inferior part of the striate sphincter is that it is horseshoe-shaped or omega-shaped [16,17]. Most researchers drew this conclusion from the serial slices of fetuses or children, and applied to adults [2, 18]. It was difficult to obtain successive sections of the pelvic organs of the adults. Although few authors tried to explore the striate sphincter on adults’ slice, they could not realize multiaxial and successive slices . The successive horizontal celloidin slices showed that the complete closed striate sphincter encircled the membranous urethra (Fig. 1d). The sagittal and coronary slices revealed that the striate sphincter also existed dorsal to the membranous urethra (Fig. 2a, 3b). So, we conclude that the inferior part of the striate sphincter was ring shaped in male adults (Fig. 4d).
McNeal et al. defined a non-glandular tissue part of prostate as AFMS. It covered the anterior surface of the prostate and extended from the bladder neck to prostatic apex. But they did not confirm the origin of AFMS . Brooks considered that AFMS migrated from the trigone . Yucel and Baskin believed that the AFMS was a developmental component of the external sphincter . Our team have proved that the upper part of AFMS originated from circular muscle of the detrusor . The superior part of the striate sphincter covered the ventral surface of prostate and formed the lower part of the AFMS (Fig. 1b, 1c and 2a). Thus, the AFMS was composed of the circular muscle of the detrusor and the superior part of the striate sphincter (Fig. 4a). Thus, we believe that the AFMS is not a part of prostate.
Myers et al. proposed that the detrusor apron was a structure connecting the bladder to the pubis, and must be considered a major component of McNeal’s AFMS . Our result displayed that the longitudinal muscle of detrusor extended downwards at the bladder neck to form the detrusor apron, and attached to the pubis (Fig. 2b). The upper part of AFMS originated from the circular muscle of detrusor, but the detrusor apron from the longitudinal muscle (Fig. 2). Additionally, there was a space between the detrusor apron and AFMS in which DVC was located. (Fig. 1a, 2b and 4a). We presumed that the function of the detrusor apron was probably to keep the anteversion of bladder body. Preservation or reconstruction of the detrusor apron in radical prostatectomy probably contribute to the stability of bladder neck.
Villers et al. considered AFMS as a thickening of the capsule, and the two structures together circled the prostatic gland . Observations of Elbadawi et al’s confirmed the upper part of the striate sphincter as an integral component of theprostatic capsule. Muscular elements of the capsule probably contribute to the distal sphincteric mechanism of urethra . Our results revealed that the capsule and AFMS formed a pocket like complex to accommodate the prostate and urethra (Fig. 4c). This complex may be a supplement of urinary control device at bladder neck and the membranous urethra. It is likely that the contraction of this complex results in sustained tension within the prostate, and then adds resistance to opening of the urethral conduit during filling to maintain continence.
More recent studies demonstrated variations of neural and vascular distribution lateral to the prostate. Walsh and Donker described a distinct NVB with bundle formation . But some authors confirmed the dispersed neural distribution, such as spray-like or curtain-like [4, 26]. Tewari et al. proposed three zones of the periprostatic nerves: proximal neurovascular plate, the predominant NVB and accessory neural pathways . Kiyoshimaet al. found that the nerves and vessels existed with bundle or dispersion formations depending on the adhesion or separation of the lateral pelvic fascia and the prostatic capsule . We found that vascular bundles lateral to prostate accompanying with nerve plexus and adipose tissue were located between the levator fascia and the capsule (Fig. 1, 3). But on the most convex region of the lateral prostate, the fascia and the capsule fused each other where we thought a safety area existed, because there was almost no adipose tissue and neurovascular bundles between them at this region (Fig. 1b, 3b). A careful capsule-levator fascia separation here may be more accordant with anatomical dissection in radical prostatectomy.
Al-Rifaei et al. reported the NVBs were divided in two parts near the prostate apex . The anterior part crossed the forepart of the membranous urethra and entered the corpus cavernosum while the posterior part crossed the membranous urethra more posteriorly to enter the bulb of the penis. Alsaid et al. demonstrated that the anterior part was cavernous nerves, and the posterior part was corpus spongiosum nerves. They both originated from the spray-like nerve fibers on lateral prostate . Our results revealed that the anterior part should be the distal part of DVC and the posterior part should be the distal part of CS (Fig. 4a, b). The distal part of DVC and the distal part of CS were separated by the posterolateral portion of striated sphincter (Fig. 4a, b). The distal part of CS was the communication between the pudendal neurovascular bundle and CS (Fig. 4a, b). Visceral nerve fibers in cavernous supply may join pudendal plexus via the distal part of CS to the corpus cavernosum. Somatic nerve fibers in pudendal nerve probably innervate the striated sphincter via the distal part of CS approach. When dealing with the apex of the prostate in nerve-sparing radical prostatectomy, we suggested to preserve the distal part of DVC and CS, which probably improved the postoperative continence and potency rates.