The Anatomy of the Scrotum

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The scrotum is the sac of skin and other tissues that holds the testicles outside of the pelvis. Its primary function is to protect the testicles, or testes, and allow them to stay cooler than core body temperature. The testicles are more functional at lower temperatures.

It is possible to experience injury to the scrotum, or diseases of the scrotum. However, most scrotum symptoms are related to the structures inside of it. Damage, or injury, to either the testes or the epididymis can cause swelling and pain in the scrotum.

Anatomy

The scrotum is part of the male anatomy. It is a sac of skin and muscle that hangs in front of the pelvis, between the legs. The scrotum is divided into two haves by the scrotal septum. In most men, one testicle sits on either side of the scrotal septum. It is common for one side of the scrotum to hang slightly lower than the other side.

Structure

The external layer of the scrotum is made of skin. Usually, this skin is darker in color than the neighboring areas of skin. Underneath the skin is the dartos muscle, or the tunica dartos. The tunica dartos helps to regulate the temperature of the testicles by contracting to reduce the surface area of the scrotum and decrease heat loss, or relaxing to increase the surface area of the scrotum to help with cooling.

Another muscle inside the scrotum is the cremaster muscle. There are two such muscles, one on each side. Each of the muscles covers the testes and the spermatic cord and reaches into the pelvis through the inguinal canal. The function of the cremaster muscles is to raise or lower the testicles. This further helps to maintain the testicles at an appropriate temperature.

The cremasteric reflex is a response to light stroking of the inner thigh. It causes the muscle to contract and the testes to elevate. It is also possible for some men to contract the cremaster muscles voluntarily.

The spermatic cord provides blood supply to the testes, vas deferens, and the cremaster muscle. It also contains nerves and lymph vessels which connect to the internal structures of the scrotum.

The scrotal septum divides the scrotum into two chambers. It is an extension of the perineal raphe, a line of tissue that extends from the anus, through the perineum, and upwards through the midline of the penis. When the testes descend in infancy, usually one testicle ends up on either side of this septum.

Anatomical Variations

There are a number of possible anatomic variations of the scrotum. In general, these variations are quite rare. However, they include:

  • Accessory scrotum: An extra scrotum that develops, usually further down the perineum, towards the anus. The accessory scrotum does not contain testes. It does not generally cause problems with the primary scrotum.
  • Bifid scrotum: This is when there is a cleft in the middle of the scrotum. It occurs when there is not enough testosterone early in development for the scrotum to fuse. Bifid scrotum often occurs alongside hypospadias.
  • Ectopic scrotum: Where the normal scrotum is located in a different location.
  • Penoscrotal transposition: Where the penis and the scrotum are located incorrectly with respect to each other. The penis can be below the scrotum (complete transposition) or in the middle of the scrotum (partial transposition.)

Function

The function of the scrotum is to protect the testes and maintain them at an appropriate temperature. The scrotum performs this function by holding the testes outside of the body and regulating how close they are to the body. A temperature cooler than core body temperature is needed for the testicles to be able to effectively produce sperm. The cremaster muscles can pull the testicles all the way into the pelvis, as needed.

Associated Conditions

A number of health conditions can affect the scrotum, as well as the structures that it protects. Looking specifically at the scrotum, cellulitis is a type of bacterial skin infection. It can occur in the skin of the scrotum, causing pain and swelling.

Hydrocele occurs when fluid builds up around the testes. Non-inflammatory edema refers to a collection of fluid within the scrotum that isn't associated with inflammation of the scrotal wall or hydrocele. This type of fluid can collect in individuals with conditions such as heart failure or liver failure.

Hematocele is a similar concern to hydrocele, except that the fluid building up around the testes is blood. This usually occurs after an injury or surgical procedure. Similarly, varicocele is where the veins in the scrotum swell. For many people, this causes no symptoms, and doesn't require treatment.

Cryptorchidism occurs when one or both of the testicles doesn't descend into the scrotum. It can repair spontaneously. However, if it doesn't, orchiopexy surgery may be needed to allow the testicle to descend. An undescended testicle can affect fertility.

Certain sexually transmitted diseases can also affect either the skin of the scrotum or its internal structures.

Other conditions that cause symptoms in the scrotum are actually associated with the testes or the epididymis. Testicular torsion is one of the few emergency conditions of the scrotum. It occurs when the testicles rotate around the spermatic cord, causing a loss of blood supply. Quick surgical correction may be needed to save the affected testicle.

Spermatocele is when the epididymis develops a fluid-filled sac. Epididymitis refers to an infected or inflamed epididymis, and orchitis to an infected or swollen testicle. Finally, testicular cancer can cause swelling and pain in the scrotum as well.

Tests

Symptoms affecting the scrotum are relatively non-specific. That means that many different conditions can present similarly at first glance. Therefore, testing is often required to diagnose the cause of any scrotal pain or swelling.

Ultrasound is usually the first type of test used to diagnose problems with the scrotum. If regular ultrasound is not effective, ultrasound with contrast can be used. Magnetic resonance imaging (MRI), with or without contrast, can also be used to diagnose conditions affecting the scrotum.

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