The scrotum is a fibromuscular cutaneous sac, located between the penis and anus. It is dual-chambered, forming an expansion of the perineum.
Embryologically, the scrotum is derived from the genital swellings. During development, the genital swellings fuse in the midline – in the adult this fusion is marked by the scrotal raphe. The scrotum is biologically homologous to the labia majora.
In this article, we shall look at the anatomy of the scrotum – its contents, blood supply and innervation.
The scrotum contains three major (paired) structures:
- Testis – the site of sperm production.
- Epididymis – situated at the head of each testicle. It functions as a storage reservoir for sperm.
- Spermatic cord – a collection of muscle fibres, vessels, nerves and ducts that run to and from the testes.
There are also muscle fibres located within the scrotum. The dartos muscle is a sheet of smooth muscle, situated immediately underneath the skin. It acts to help regulate the temperature of the scrotum, by wrinkling the skin – this decreases surface area, reducing heat loss.
The scrotum receives neurovascular supply from the nearby vessels and nerves. This is in contrast to the testes – which carry their vessels, nerves and lymph drainage from the abdomen during their development.
The scrotum receives arterial supply from the anterior and posterior scrotal arteries. The anterior scrotal artery arises from the external pudendal artery, while the posterior is derived from the internal pudendal artery.
The scrotal veins follow the major arteries, draining into the external pudendal veins.
Cutaneous innervation to the scrotum is supplied via several nerves:
- Genital branch of genitofemoral nerve – derived from the femoral plexus and supplies the anterolateral aspect of the scrotum.
- Anterior scrotal nerves – derived from the ilioinguinal nerve and supplies the anterior aspect of the scrotum.
- Posterior scrotal nerves – derived from the perineal nerve and supplies the posterior aspect of the scrotum.
- Perineal branches of posterior femoral cutaneous nerve – derived from the sacral plexus and supplies the inferior aspect of the scrotum.
The lymph fluid drains to the nearby superficial inguinal nodes.
Clinical Relevance: Enlargement of the Scrotum
The scrotal sac is very distensible, and will enlarge in response to the size of its contents. There are a number of causes of scrotal swelling – here are the most common:
- Inguinal hernia – where the contents of the abdominal cavity protrude into the scrotum, via the inguinal canal.
- Hydrocoele – a collection of serous fluid within the tunica vaginalis. It is most commonly due to a failure of the processus vaginalis to close.
- Haematocoele – a collection of blood in the tunica vaginalis. It can be distinguished from a hydrocoele by transillumination (where a light is applied to the testicular swelling). Due to the dense nature of blood, light is unable to pass through.
- Varicocoele – gross dilation of the veins draining the testes.The left testicle is more commonly affected, as the left testicular vein drains into a smaller vessel, the left renal vein, at a perpendicular angle. A large varicocoele can look and feel like a bag of worms within the scrotum.
- Epididymitis – inflammation of the epididymis, usually caused by bacterial or viral infection.