Anatomy, Abdomen and Pelvis: Testes

Structure and Function

The testis is the male reproductive gland responsible primarily for producing sperm and androgens. Testosterone levels are controlled by the release of Luteinizing Hormone (LH) from the anterior pituitary gland, whereas follicle-stimulating hormone levels control sperm production.

Embryology

The testes start as an undifferentiated gonad in the retroperitoneum. The testis-determining factor (SRY gene) present on the Y chromosome causes the gonad to differentiate into testes. In females, the SRY gene is absent; hence, the gonad develops into an ovary. As the fetus starts to mature, the testes begin to produce the male sex hormone, testosterone. This sex hormone permits the development of the male genitalia.[3] The tunica albuginea forms a connective tissue layer between the seminiferous tubules and the rest of the testis through invagination. The Sertoli cells begin producing Müllerian-inhibiting Substance (MIS), which causes regression of the Müllerian ducts at 8 to 10 weeks. The only remaining remnants of the Müllerian ducts in an adult male are the appendix testis and the prostatic utricle.

During the third trimester of pregnancy, the testes, which are located in the abdomen, start their descent into the inguinal canal and then to their final destination in the scrotum. During this journey, they pass through the peritoneum, the abdominal wall, and the inguinal canal. During development, the inguinal canal contains the processus vaginalis, which is a structure that develops from the peritoneum. It allows the testes to descend, then eventually undergoes apoptosis, becoming the tunica vaginalis, which surrounds part of the testis. Failure of the closure of the processus vaginalis may lead to complications such as a communicating hydrocele and an inguinal hernia.[4] 

Blood Supply and Lymphatics

The testicular arteries supply blood to the testes. They arise from the anterolateral segment of the abdominal aorta just below the origin of the renal arteries. The vessels travel in the retroperitoneum and cross over the ureter, pass through the deep inguinal ring, and join the spermatic cord. Additional blood supply to the testes comes from the artery of the vas deferens and the cremasteric artery. Venous drainage from the testes is via the pampiniform plexus, which lies anterior to the vas deferens. The veins converge superiorly to form the testicular vein. The right testicular vein joins the vena cava, and the left testicular vein drains into the left renal vein. Drainage of the lymphatics from the testes follows the same path as the testicular arteries and drains to the preaortic lymph nodes.[5]

Nerves

The testes have innervations from both sympathetic and parasympathetic fibers.[6]

Muscles

As the testes move from the abdomen into the scrotum, it is gradually enveloped by several layers of muscle tissue, the internal spermatic fascia, the cremasteric muscle and fascia, and the external spermatic fascia. The daily degree of testicular descent varies primarily according to temperature. This is controlled by the cremaster muscles.[7]

Physiologic Variants

Two vestigial embryonic structures with no known physiologic function include the following:

• At the cranial end of the paramesonephric duct (Müllerian duct), sometimes one finds the appendix testis. This pear-shaped vestigial structure is found in about 2% of testes, and it is typically located at the superior pole in the groove between the head of the epididymis and the testis.
• Also, at the cranial end of the mesonephric duct, one sometimes finds the appendix of the epididymis, which is present in about 25% of testes. Their location is variable but is often located at the head of the epididymis.
• In about 7% of males, the epididymis may be located on the anterior surface of the testis.

Surgical Considerations

Cryptorchidism is an important disorder to recognize early in life, not only to preserve sterility but also to reduce the risk of testicular cancer. Unless the surgeon can surgically bring the testes back into the scrotum, where they can be under surveillance, the undescended testes should be removed. It is also important to know that there is an increased risk of cancer in the contralateral testes, and hence regular self-examinations are highly recommended.[8][9] Sometimes serous fluid can accumulate in between the layers of the tunica vaginalis, leading to a hydrocele. This could be triggered by inflammation, trauma, or a congenital cause due to persistent communication with the abdominal cavity.

In young men, testicular torsion is a surgical emergency. The blood supply must be restored within 6 hours of symptom onset; the testes must be fixed in the scrotum to prevent recurrence. Most urologists also fix the contralateral testes at the same time. The descent of the testes may be delayed or arrested along the course in the inguinal canal and may be complicated by an inguinal hernia. All true undescended testes have associated inguinal hernias. This is not true for retractile testicles. 

Clinical Significance

Cryptorchidism (non-descent of the testis) not only leads to infertility but also carries a risk of testicular cancer. If the abnormal testis is not removed, close surveillance is necessary. The primary treatment for cryptorchidism is repositioning the cryptorchid testes, known as orchidopexy. It should be performed before 1 year of birth in those with congenital cryptorchidism in order to best prevent cancer.[10] Sometimes, a hydrocele (serous fluid) can result when fluid collects between the layers of the tunica vaginalis. A hydrocele may be due to an infection, trauma, or congenital factors. One common congenital factor is the incomplete closure of the processus vaginalis.[4]

Other Issues

In premature infants, the descent of the testes is often not complete. Thus, after birth, attention should be paid to the undescended testes. In some cases, the testes may exit the superficial inguinal ring but may then pass between the thigh and scrotum to rest in the perineum, resulting in an ectopic testis.