The tunica albuginea of the penis lends great flexibility, rigidity and tissue strength to the penis . It consists of an inner circular and an outer longitudinal layer . Intracavernosal pillars arise from the inner layer and radiate into the corpora cavernosa (CC). Together with the septum, theyprovide support to the erectile tissue [3, 4]. The corpus spongiosum lacks the outer layer and the intracorporeal pillars .
The anatomical data regarding the origin, morphology, as well as nerve and blood supply of the bulbocavernosus muscle (BCM) and ischiocavernosus muscle (ICM), are well documented in the literature [5, 6, 7, 8]. However, the exact mode of insertion of these muscles into the TA of the penile shaft needs to be described more clearly. Detailed knowledge of the mode of attachment of the BC and IC muscle fibers into the penile TA seems necessary for a better understanding of the role of these muscles in the mechanism of erection. In the current communication, we studied the penile TA and the mode of insertion of the IC and BC muscles into it.
MATERIAL AND METHODS
The study was comprised of 28 cadaveric specimens: 18 adult (mean age 37.3 ± 8.6 SD years, range 26–48) and 10 fully mature neonatal cadavers. All the cadavers had normal genitourinary organs. The obtained specimens consisted of the perineum and included the penis with its bulb and crura and parts of the ischial tuberosities to allow for collection of the cavernosus muscles from origin to insertion. The specimens were fixed in 10% formalin. The TA and the mode of insertion of the cavernosus muscles into the penis were studied by the naked eye with the help of a magnifying loupe and bright light. Sections for microanatomical studies were then taken from the penile shaft and the root including the bulb and crura. The specimens were stained with hematoxylin, eosin and Verhoeff van Gieson stain. Each section was studied for the TA structure and the relation of the two cavernosus muscles to it.
In all 28 cases, the TA of the CC consisted of collagen fibers impregnated with few elastic fibers. The collagen fibers were arranged in bundles in a wavy pattern. In 20 cadaveric specimens, the TA of the CC was formed of two layers: an inner circular and an outer longitudinal (Figure 1). In six of the 28 specimens, it consisted of three layers: an inner circular, intermediate longitudinal and outer circular (Figure 2). In the remaining two specimens, the TA was formed of a single longitudinal layer (Figure 3). At the junction of the CC with the corpus spongiosum (CS) in all the studied specimens, the TA of the CC consisted only of the circular layer. The TA of the CS consisted of only one layer with circularly orientedfibers; no longitudinal fibers were detected in any of the specimens examined.
Mode of Insertion of the Bulbo-/Ischio-Cavernosus Muscles into the Tunica Albuginea
The BCM lay over the penile bulb and its muscle bundles were arranged in 3 groups: 2 lateral and 1 median (Figure 4). The lateral fibers were inserted into the perineal membrane. The median fibers were grouped together forming a ribbon that extended over the penile bulb and the proximal part of the CS, where it bifurcated into two limbs (Figure 4). Each limb proceeded laterally forward and approached the ICM at the lateral surface of each CC. The two muscles fused, forming one muscular limb, which, in 18 cadavers, ended in tendinous fibers that, together with the contralateral fibers, formed a fibrous belt over the dorsum of the 2 CCs. In 6/28 cadaveric specimens, the conjoint limb continued over the CC dorsum as fleshy fibers; it contained no tendinous fibers (Figure 5). In the remaining 4/28 specimens, the conjoint limb of the BCM and ICM was attached on each side to the lateral surface of the CC (Figure 6); no extension forming a belt over the dorsum of the CC was found.
The current study could shed some light on the structural-functional adaptation of both the TA and cavernosus muscles’ insertion to the erectile mechanism. The TA consisted mainly of collagen fibers that are inextensible. However, the wavy pattern of collagen in the flaccid state of the penis, as well as the impregnation of the TA with few elastic fibers, apparently give the TA a degree of expandability during erection.
Variations in the morphologic structure of the TA of the CC were detected. The two-layered TA was the most common with 71.4%, while the three-layered TA was encountered in 21.4% and the single layer in 7.2%. The exact significance of the structural variations of the TA during erection is not known. It is likely that the degree of tumescence depends on the TA structure. Thus, we assume that the triple-layered TA gives more firmness to penile erection than the single or double-layered TA. Similarly, the TA of 2 layers, which is the most common pattern, would provide a stronger erection than the single layer. This comparison of the role of the different layers of the TA in erection seems applicable, provided the other factors of penile erection are standardized. Alternatively, it might be that the increase of the TA layers impede the erectile process. On the other hand, the CS is covered by a single layer of TA, and this fact might diminish its rigidity on erection compared to the rigidity of the CC. However, the role of the different layers of the TA in erection needs to be investigated.
As regards to the mode of cavernosus muscles’ insertion into the TA, 3 patterns were encountered: fibrous belt, muscular belt and beltless. The fibrous belt insertion of the 2 cavernosus muscles was the most common pattern, representing 75% of the studied specimens. Meanwhile, the muscular belt occurred in 21.5% and the beltless type in 3.5%. The role of the different patterns of insertion of the conjoint cavernosus muscles in the TA is not known. The belt form, fibrous or fleshy, of cavernosus muscles’ insertion appears to be more efficient in compressing the CCs during erection than the beltless type. Furthermore, the fibrous belt apparently effects a firmer CC compression than the muscular belt. The role during erection, however, of the different patterns of cavernosus muscles insertion into the CCs needs to be studied further.
In conclusion, the TA occurred in three histomorphologic patterns: single, double and triple layers, the most common being the double-layered pattern. The different TA patterns are suggested to affect penile rigidity of various degrees during erection. Furthermore, the 3 types of cavernosus muscles’ insertion into the TA (fibrous, muscular belt or beltless) appear to produce variable degrees of CC compression. However, further studies are required to investigate the role of the different types of TA and cavernosus muscles’ insertion in the mechanism of erection.
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