The scrotum is a pouch of skin and fascia derived from the anterior abdominal wall and contains the testes, epididymides and the lower parts of the spermatic cords (Fig. 4.25).
Skin and subcutaneous tissue
The skin of the scrotum is supplied anteriorly by the external pudendal vessels and innervated by the ilioinguinal nerve. The remainder of the scrotal skin is supplied by branches of the internal pudendal vessels and branches of the pudendal nerve and posterior cutaneous nerve of thigh. Lymph drains to the superficial inguinal nodes.
Deep to the skin lies the subcutaneous tissue, continuous superiorly with the subcutaneous tissue of the abdominal wall. The scrotal subcutaneous tissue, which contains smooth muscle called dartos, but little fat, forms a median septum, dividing the pouch into right and left sides.
Deep to the subcutaneous tissue of each side of the scrotum lie three layers of spermatic fascia (Fig. 4.26). Each layer takes the form of a sleeve derived from one of the layers of the abdominal wall.
The outermost sleeve, the external spermatic fascia, begins at the superficial inguinal ring and is continuous with the external oblique aponeurosis (Fig. 4.20).
The intermediate sleeve is the cremasteric fascia and muscle, continuous within the inguinal canal with the internal oblique muscle (Fig. 4.21). The transversalis fascia of the abdominal wall (Fig. 4.22) provides the deepest sleeve, the internal spermatic fascia, which commences at the deep inguinal ring. These three fascial layers surround the components of the spermatic cord and continue downwards to enclose the testis and epididymis.
The spermatic cord runs from the deep inguinal ring into the scrotum, terminating posterior to the testis. The cord comprises the ductus (vas) deferens and the vessels and nerves of the testis and epididymis (Fig. 4.27) surrounded by the layers of spermatic fascia (Fig. 4.26).
The principal artery of the spermatic cord is the testicular artery, a branch of the abdominal aorta (Figs 4.88 & 4.89). Also present is the artery to the ductus deferens (Fig. 4.28), usually arising from the superior vesical artery within the pelvic cavity. The veins draining the testis and epididymis form a network, the pampiniform plexus. Occasionally, these veins become dilated (varicocele; p. 188). From this plexus, one or two veins continue through the deep inguinal ring and ascend the posterior abdominal wall with the testicular artery (Fig. 4.88). The testicular vessels are accompanied by a plexus of autonomic nerves and by lymph vessels which terminate in the aortic lymph nodes.
The tunica vaginalis is a closed serous sac, which covers the medial, anterior and lateral surfaces of the testis and the lateral aspect of the epididymis (Figs 4.25 & 4.27). Like the peritoneum from which it is derived, the tunica vaginalis has parietal and visceral layers separated by a small quantity of serous fluid. An excessive accumulation of fluid in the sac produces a swelling (hydrocele) anterior to the testis.
In the fetus, the processus vaginalis links the tunica vaginalis with the peritoneal cavity. Usually, the processus closes before birth, but occasionally it remains patent and is associated with infantile hernia.
The testis is an ovoid organ approximately 5 cm long in the adult, suspended by the spermatic cord in the lower part of the scrotum with its superior pole tilted slightly forwards (Fig. 4.28). The testis has a thick fibrous capsule, the tunica albuginea, which is covered laterally, anteriorly and medially by the visceral layer of the tunica vaginalis (Fig. 4.25). The posterior surface of the organ, devoid of a covering of tunica vaginalis, is pierced by the efferent ductules, branches of the testicular artery and numerous small veins that form the pampiniform plexus (Figs 4.28 & 4.29).
Although the testis usually completes its descent into the scrotum by the time of birth, it may remain in the abdomen or the inguinal canal. In this case, surgical intervention is usually advised.
The testis may rotate, twisting the spermatic cord (torsion). The arterial supply is threatened and urgent surgical correction is needed to prevent necrosis of the testis. Tumours of the testis are common in young adults and may metastasize to the para-aortic nodes. Treatment involves removal of the organ (orchidectomy).
The epididymis consists of a narrow, highly convoluted duct applied to the posterior surface of the testis (Fig. 4.29). Its broad superior part, the head, overhangs the upper pole of the testis, from which it receives several efferent ductules (Fig. 4.28). The body of the epididymis tapers into the tail, which is continuous with the ductus deferens. The epididymis is supplied by branches of the testicular artery and drained by the pampiniform plexus.
The ductus deferens is approximately 25 cm long and connects the tail of the epididymis with the ejaculatory duct in the prostate gland. The ductus ascends behind the testis on the medial side of the epididymis and continues upwards in the cord. When the upper part of the scrotum is palpated, the ductus can be distinguished from the accompanying testicular vessels by its firmness.
After traversing the inguinal canal, the ductus runs backwards across the pelvic brim and along the lateral wall of the pelvis (Fig. 4.23) before terminating in the ejaculatory duct (Fig. 5.24).