Scrotal Wall
A detailed understanding of the scrotal anatomy is critical in the operative planning of scrotal and pelvic surgeries. Knowledge of scrotal wall anatomy enables safer access into the scrotum for common scrotal procedures, facilitates identification of surgical planes during surgical debridement, and allows for multilayer closures.
The scrotal skin is rugated because of its underlying attachment to the dartos muscle, deeply pigmented, and hair-bearing. In contrast with other parts of the body, the scrotum is elastic and highly-temperature regulated to enable spermatogenesis.
Scrotal Contents
Scrotal contents are maintained in their position within the scrotal cavity by the spermatic cord and gubernacular attachments. The testicle is intimately encased by the tunica albuginea, and protected by the layers of tunica vaginalis, internal and external spermatic fascia (separated by a layer of cremasteric muscle), and ultimately covered by the dartos layer and scrotal skin. The dartos fascial layer acts as a barrier to the spread of necrotizing fasciitis to deeper structures in the scrotum (Figs. 83.1 and 83.2).
The epididymis originates from the efferent ducts of the rete testis in mediastinum testis. It is located along the posterolateral aspect of the testis, with its head (caput) located superiorly, the body (corpus)
along the longitudinal axis of the testis, and the tail (cauda) at the inferior testicular pole. The vas deferens begins as continuation of the cauda epididymis, travels along the spermatic cord into the pelvis, where it becomes ampulla of the vas, joins with seminal vesicles (SVs), and forms the proximal ejaculatory duct. Two nonfunctional, vestigial structures may be encountered in the scrotum: the appendix testis over the upper pole of the testis and the appendix epididymis attached to the head of the epididymis.
Vasculature
The scrotum is highly vascularized, with blood supply provided anteriorly from the superficial external pudendal artery and deep external pudendal artery, and posteriorly from the posterior scrotal artery. Venous drainage follows the arterial supply draining into the external pudendal vein and posterior scrotal vein, which empty into the great saphenous vein and to the internal iliac veins, respectively.
In addition to temperature regulation, the thin, highly vascular nature of the scrotal skin allows increased transdermal medication absorption, up to 40 times the absorption of other parts of the body (Nieschlag and Behre, 2010). This absorptive quality of the scrotal skin was utilized in testosterone supplementation; however, the necessity of frequent scrotal hair clipping made continued application of scrotal testosterone patches cumbersome for patients, and this formulation of testosterone is no longer available. Additionally, the scrotal skin is high in 5α-reductase enzyme, and as result, high dihydrotestosterone levels were seen with scrotal transdermal testosterone therapy (Ahmed et al., 1988).
The blood supply to the testis arises from the aorta as the testicular artery, from the internal iliac artery as the artery to the ductus deferens, and from the external iliac artery as the cremasteric artery. The epididymis is nurtured by the superior epididymal artery from the testicular artery and from the inferior epididymal artery, arising as branches off the deferential artery and distal branches of the testicular artery. Although the majority of the blood supply (~84%) to the epididymis comes from the superior epididymal artery, the superior epididymal artery can be sacrificed to gain additional testicular mobilization during vasectomy reversal because of the vascular anastomoses between the superior and inferior epididymal artery (Strittmatter and Konrad, 1989). Understanding the blood supply to the epididymides is important in the surgical treatment of epididymal disease. Important anastomoses are also present cranial and caudal to the testis. Cranially, thin-caliber anastomoses are often present in the spermatic cord between the testicular artery and the deferential artery approximately 10 cm above the testis (Strittmatter and Konrad, 1989). At the level of the cauda of the
epididymis, anastomoses form between the testicular artery, deferential artery, and cremasteric artery. This redundancy of blood supply to the testis allows viability of the testis if one or two of the arteries are injured or ligated.
Innervation
The scrotum is innervated by autonomic and somatic nerve fibers. Three groups of converging autonomic nerve fibers contribute to the autonomic innervation of the testes: (1) superior spermatic nerves, from the renal and mesenteric plexi, which follow the testicular artery, (2) middle spermatic nerves, from the superior hypogastric plexus, which travel adjacent to the vas as it enters the internal spermatic ring, and (3) inferior spermatic nerves, which originate from the inferior hypogastric plexus (Patel, 2017). The inferior spermatic nerve fibers fuse with the middle spermatic nerve fibers at the prostate-vesical junction, run within the spermatic cord along the vas deferens, and ultimately penetrate the epididymis and testis (Sosa et al., 2009; Patel, 2017). In addition to the sensory fibers contained in the autonomic spermatic nerves, afferent fibers of these nerves are also important in the endocrine control of the testis. Sosa et al. demonstrated the endocrine control over testis function by modulating androgen release in adult male rats via exposure of autonomic ganglia to adrenoreceptor agonists and antagonists (Sosa et al., 2009). Exposure of the inferior mesenteric plexus ganglia to noradrenaline resulted in significantly higher serum testosterone levels compared with untreated ganglia in the control male rats; however, noradrenaline exposure to the superior mesenteric ganglia did not influence testosterone concentrations. The scrotum is also innervated by somatic nerves, including ilioinguinal and genitofemoral nerves. The genital branch of the genital femoral nerve is positioned on the inferolateral aspect of the spermatic cord and innervates the anterolateral scrotal skin, the tunica vaginalis, and the cremaster muscles (Ducic and Dellon, 2004; Zorn et al., 1994). In contrast, the ilioinguinal nerve sits on the anterior of the cremasteric muscles and innervates the anterior scrotal skin (Wijsmuller et al., 2007). An understanding of the course of these nerves is important in scrotal denervation procedures, which are discussed later in this chapter.
