Back to temperature regulation by the scrotum: the skin of the scrotum is characterized, like that of the eyelids, by the absence of subcutaneous fat, the presence of many tiny blood vessels, and a layer of muscle directly under the skin. Fat insulates too well, which does not help the ability to react rapidly to cold or heat. The muscular layer beneath the skin is called the tunica dartos. As we grow older the tunica dartos slackens, so that in elderly men the scrotum becomes larger and smoother. Everything starts to hang: it comes to resemble a set of bells. In cold temperatures the scrotum shrinks and when it is hot the muscle layer relaxes and the scrotum expands.
‘Croat traps testicles in sun lounger’, read a recent newspaper headline. Trying to stand up and finding to your annoyance that your testicles are trapped between the slats of your lounger is no joke. But it happened to Mario Visnjic after he had swum naked around the harbour of Valalta (Western Croatia). Mario had no inkling of danger when he sat down in his chair to get his breath back after his cold dip. The cold sea had caused his testicles to shrink, so that they dropped between the wooden slats of the lounger. When a little later the sun did its work and the testicles expanded to their true size again, the damage was done. His rescuer had no alternative but to cut the lounger in half and release the unfortunate victim!
The blood supply to the scrotum is through the large inguinal artery, the deep pelvic artery and the abdominal wall artery. Lymphatic drainage takes place through the superficial lymph glands in the groin.
It is important for the reader with hypochondriac tendencies to know exactly how lymphatic drainage works: this will help doctors to know exactly where to look for metastases.
The skin of the scrotum is fairly sensitive. Delicate nerve-endings are designed to maximize pleasure. Swellings on the skin of the scrotum are almost always sebaceous cysts. Treatment is necessary only if there is an infection. Swellings of the content of the scrotum, the testicles and epididymis are much more common. Various sections will be devoted to these in later chapters.
The blood supply to the testicles is closely related to that to the kidneys because of their common embryological origin. The main artery in the testicle (arteria testicularis) branches off the aorta just below the renal artery. The artery runs behind the abdominal cavity through the inguinal canal to the testicle. There are connections to the seminal duct artery. The latter is a branch of the main inguinal artery. In the seminal cord there is a tangle of arteries (plexus pampiniformis), from where blood flows back to the heart. On a level with the internal ring of the inguinal canal this complex becomes the drainage vein (vena spermatica interna). On the right-hand side this flows directly into the inferior vena cava, and on the left into the renal vein. This division is the reason why varicose veins in the scrotum, varicocele, are much more common on the left than on the right.
Lymphatic drainage from the testicles is in the first instance into lymph glands behind the abdomen and not, as many people think, into glands in the groin. That fact is particularly important in the treatment of testicular cancer. The lymph glands in the groin do, however, form part of the drainage system of lymph from the skin of the scrotum. In the past cancer of the skin of the scrotum was very common among chimney sweeps and coalmen, who had soot and coal dust more or less continually in their crotch. Today cancer of the skin of the scrotum is extremely rare.