Very simply, the scrotum is a cutaneous sac that contains the testes, or testicles, and the lower parts of the spermatic cord. Importantly, the scrotum allows the testes to be positioned outside of the body.
|Layers||Skin, dartos fascia (dartos muscle)|
|Contents||Testes, epididymis, vas deferens (spermatic cord)|
|Function||Maintenance of proper temperature for spermatogenesis|
|Blood supply||Posterior scrotal branches of the perineal artery, anterior scrotal branches of the superficial external pudendal artery, cremasteric artery|
|Innervation||Genital branch of the genitofemoral nerve, anterior scrotal nerves, posterior scrotal nerves, perineal branches of the posterior cutaneous nerve of the thigh|
To understand the significance of this anatomical structure and its location, this article will discuss the development and anatomy of the scrotum, its contents and function, its blood and nerve supply, and the clinical significance of the scrotum, especially in infant males.
Development and Anatomy
In the embryo, the scrotum develops from a pair of ridges or elevations, that form on either side of the embryonic genital tubercle. The tubercle will later develop into the penis in the male, or the clitoris in the female. The elevations on either side of the tubercle are known as labioscrotal swellings, as they will later develop into either the scrotum in males, or into the labia majora in females. As the embryo continues to develop and become a fetus, the separated pair of labioscrotal swellings will fuse at the midline, creating one continuous sac, the scrotum. Towards the end of pregnancy, approximately 32 weeks, both testes have completed their descent from the posterior abdominal wall, through the inguinal canal, to finally reach the scrotum.
Because of the pathway of descent through the anterior abdominal wall, the testes will be covered by the layers of fascia and muscles (external and internal obliques, and transversus abdominis) associated with the abdominal region. The scrotum however, has only two layers, because it develops separately from the testes. Externally is the skin, and below the skin a layer of fascia known as dartos fascia. This fascial layer is devoid of fat but does include smooth muscle fibers collectively known as the dartos muscle. Since the fascial layer, including its muscle fibers, attaches to the overlying skin, when the dartos muscle contracts it gives the scrotum its wrinkled appearance.
Internally, the dartos fascia will divide the scrotum into right and left compartments to house each of the testes. This internal fascial septum, or wall, can be visualized externally as a ridge of skin known as the scrotal raphe. The scrotal raphe indicates the line of fusion of the labioscrotal swellings in the embryo.
As mentioned previously, the scrotum contains the testes and parts of the spermatic cord. The testes are the site of sperm production, and as such, form the essential component of the male reproductive system. Sperm leaves the testes via the epididymis, which then drains into the ductus or vas deferens. The epididymis and lower portions of the ductus deferens are located within the scrotum. The ductus deferens is joined by blood vessels supplying the testes, creating the contents of the spermatic cord.
It is sperm production, or spermatogenesis, in the testes that highlights the essential function of the scrotum. The production of sperm is most efficient within a small range of temperature. The presence of the testes in the scrotum means they are located just outside of the body, allowing them to be slightly cooler than the internal body temperature.
However, if the temperature of the testes drops, the dartos muscle of the scrotum, and the cremaster muscle (one of the layers covering the testes), will contract, pulling the scrotum and the testes closer to the body. This will raise the temperature in the testes. On the other hand, if the temperature in the testes is too high, the dartos and cremaster muscles can relax, lowering the scrotum and testes away from the body, and consequently lowering the temperature of the testes.
- Posterior scrotal branches of the perineal artery: Arise from the internal pudendal artery, which is a branch on the internal iliac artery.
- Anterior scrotal branches of the external pudendal artery: The external pudendal artery branches directly from the femoral artery, a continuation of the external iliac artery.
- Cremasteric artery: A branch of the inferior epigastric artery, which arises from the external iliac artery.
- Genital branch of the genitofemoral nerve: Arising from the lumbar plexus, this branch (L1,2) supplies the anterolateral surface of the scrotum.
- Anterior scrotal nerves: These are branches of the ilioinguinal nerve (L1) from the lumbar plexus. They supply the anterior surface of the scrotum.
- Posterior scrotal nerves: Arise from the perineal branch of the pudendal nerve (S2-4) which forms from the sacral plexus. They supply the posterior surface of the scrotum.
- Perineal branches of the posterior cutaneous nerve of the thigh: These branches arise from a nerve from the sacral plexus, the posterior cutaneous nerve of the thigh (S2,3). They supply the inferior surface of the scrotum.
The presence of the scrotum and testes outside of the body is important for parents of newborn male babies. In about 3% of full-term babies and 30% of premature infants, the testes do not descend into the scrotum but remain inside the body. This irregular positioning of the testes is called cryptorchidism and it is detectable because the scrotum is located outside of the body, and can be palpated to check for the presence of both testes. This is an important check to perform as cryptorchidism affects the fertility and also undescended testes are at a greater risk of becoming malignant or cancerous.