Urogenital disorders

III./1.1.: Testis (orchis)

III./1.1.1.: General anatomy

The testis (orchis), weighing 15-25 g, is a paired, flattened plum-shaped organ. The testes are located in the scrotum where the temperature is optimal (lower than the body temperature) for the reproductive (spermatogenetic) function. Therefore, in the fetal life the testes descend from the abdominal cavity into the scrotum (descensus testiculorum). Besides its reproductive function, the testis also has an endocrine (androgen hormone secreting) function.

Flexible to palpation, the testis is slightly flattened medio-laterally; therefore medial and lateral surfaces can be distinguished on it. It measures in approximately 4-5 cm length; the left testis in most of the cases is slightly larger and hangs lower. The testis sits obliquely with its long axis (connecting the upper and lower poles) slightly tilting laterally and anteriorly, so the superior pole points anterolaterally. The lower pole is anchored by a short band, the remnant of the gubernaculum testis to the coverings of the testis (to the tunica dartos). The anterior margin of the testis is rounded and free, the posterior edge is straighter and fused with the epididymis. The head of the epididymis (caput epididymidis) contacts the upper pole of the testis, below that the body (corpus epididymidis) and tail of the epididymis (cauda epididymidis) can be seen. The latter is continuous with the vas deferens (ductus deferens) through that the sperm is propelled into the prostatic part of urethra.

At the upper pole of the testis, two embryological remnants are located: the appendix epididymidis (the remnant of the mesonephros) and the pear-shaped appendix testis (the remnant of the cranial end of the Müller /paramesonephric/ duct).

The outer surface of the testis is enveloped by a tight, fibrous capsule, the bluish-white tunica albuginea. The outer side of tunica albuginea is covered by the peritoneum (therefore it has a smooth, glossy appearance) since the peritoneum forms a small, separate sac (tunica vaginalis testis) surrounding the testis. This small peritoneal cavity is formed by the parietal (periorchium) and visceral (epiorchium) layers; between these layers a small serous cavity is placed surrounding the testis and epididymis; between these organs a peritoneal pouch (sinus epididymidis) is formed. The parietal layer of the tunica vaginalis faces towards the inner layers of the coverings of testis (so it is fused with the /internal/ spermatic fascia - which is the continuation of the transversalis fascia of the abdominal wall). The visceral layer of tunica vaginalis is tightly fused with the tunica albuginea of the testis. The reflexion of the parietal and visceral peritoneal layers (mesorchium) is situated on the posterior side of the testis. The cavity of the tunica vaginalis houses a small amount of serous fluid; the pathological accumulation of this fluid causes the hydrocele of the testis.

The tunica vaginalis testis developmentally corresponds to the lower end of processus vaginalis testis: this is a peritoneal protrusion which extends downwards - before the testicular descent – into the scrotum. After the testes have finished their descent along this, the processus vaginalis shrinks, its lumen is obliterated, and the remnant (vestigium processus vaginalis) can be seen as a dense, connective tissue bundle.

The connective tissue of the tunica albuginea sends fine processes (septula testis) into the testis, dividing it into approx. 200-250 wedge-shaped lobules (lobuli testis). These lobules contain irregularly twisted ducts, the convoluted seminiferous tubules, usually 1-4 tubules per lobule. When cutting the tunica albuginea, these ducts can be drawn from the testis as fine ‘fibers’.

In these tubuli the formation of sperm cells (spermatogenesis) takes place; in the connective tissue between the ducts the androgen secreting interstitial cells of Leydig can be observed. The convoluted seminiferous ducts finally converge to the mediastinum testis (found at the posterior-superior part of the organ), and are continuous with the short, straight seminiferous tubules. In the wall of these tubuli seminiferi recti occurs already no spermatogenesis. From there, the developing sperm cells move on to the labyrinthic spaces of rete testis of Haller, then to the ductuli efferentes testis (the latter is found in the epididymis).

The tunica albuginea becomes thicker at the posterior side of the testis and continues into the organ at the mediastinum testis. At that area can the blood vessels, nerves enter the testis and the ductuli efferentes leave the organ, heading to the epididymis.

Under the firm connective tissue of tunica albuginea the tunica vasculosa with looser connective tissue rich in blood vessels is discernable.

III./1.1.2. The blood supply of the testis

The gonadal arteries, in males the testicular arteries are one of the paired visceral branches of the abdominal aorta. The testicular arteries start from the aorta at the level of the original fetal development site of the testis, at L2 vertebral level, below the renal arteries. This embryological fact explains the long course of the vessel, having no important side branches. The gonadal arteries run on the posterior abdominal wall, on the anterior surface of psoas major muscle, retroperitoneally. It crosses the ureter anteriorly then -as a member of the spermatic cord- enters the inguinal canal. Exiting at the superficial (external) opening of the inguinal canal courses further downwards into the scrotum and enters the testis (at the posterior-superior part of the organ) and gives its branches to supply the testis.

The gonadal arteries, in males the testicular arteries are one of the paired visceral branches of the abdominal aorta. The testicular arteries start from the aorta at the level of the original fetal development site of the testis, at L2 vertebral level, below the renal arteries. This embryological fact explains the long course of the vessel, having no important side branches. The gonadal arteries run on the posterior abdominal wall, on the anterior surface of psoas major muscle, retroperitoneally. It crosses the ureter anteriorly then -as a member of the spermatic cord- enters the inguinal canal. Exiting at the superficial (external) opening of the inguinal canal courses further downwards into the scrotum and enters the testis (at the posterior-superior part of the organ) and gives its branches to supply the testis.

The arteries running in the scrotum and in the spermatic cord (testicular a., deferential a. and the cremasteric branch of inferior epigastric a.) have several anastomoses, therefore the testis, epididymis and ductus deferens can receive their blood supply from multiple sources. It has practical significance: in case the testicular artery is not able to provide adequate blood supply due to any problem (vascular block) during its long course (e.g. due to an abdominal compression), the other arteries can still give an appropriate nutrition to the testis. However, if the compression or vascular block occurs distal from the inguinal canal, there is no possibility to ensure adequate circulation.

The branches of the testicular artery form a rich vascular network under the capsule of the testis in the tunica vasculosa. The vessels run around the seminiferous ducts; there an immunologically important blood-testis barrier is made between the capillaries and the wall of the seminiferous tubules in order to protect the developing sperm cell precursors.

III./1.1.3.: The venous drainage of the testis

The venous drainage of the testis is served by the rich venous network of the pampiniform plexus. These veins are of muscular type; surrounding the testicular artery, making a tortuous venous mesh around it. It has a practical significance: the blood of the testicular artery would be too warm (due to the body heat) but here the venous blood - as a counter-current heat exchanger – cools the blood heading to the testes efficiently. The several veins of the pampiniform plexus form 3-4 veins when coursing upwards in the inguinal canal and finally, reaching the abdominal cavity they usually converge into two veins (testicular veins), accompanying the testicular artery.

The right testicular vein empties –forming an acute angle – into the inferior vena cava, while the left testicular vein enters perpendicularly into the left renal vein (which drains also into the inferior vena cava). This difference of the venous drainage has developmental explanation (the gonadal veins develop from the caudal parts of subcardinal veins; the right subcardinal vein also gives rise to the subcardinal part of the inferior vena cava; the inter-subcardinal anastomosis will form the left renal vein). This fact results a hydrodynamic vulnerability and therefore explains the difference seen in the venous diseases of the testes (varicokele): the left testis can develop more often (and earlier) venous problems. If only the right testis is involved in varicokele, either situs inversus or other problems (e.g. tumor along the course of the right testicular vein) should be considered.

III./1.1.4.: The lymphatic drainage of the testis

The lymphatic drainage of the testis occurs through the spermatic cord along the pampiniform plexus; the lymphatics reaching the abdominal cavity end in the paraaortic lymph nodes (at the approximate level of the original position of the testes in the abdominal cavity). When testicular cancer is suspected, the ways of lymphogen metastases usually lead here. The lymphatics from the scrotum, however, drain into the superficial inguinal lymph nodes.

III./1.1.5.: The nerves of the testis

The sympathetic nerves reach the gonad via the testicular plexus. The postganglionic sympathetic nerve fibers run –as branches of the abdominal aortic plexus- along the testicular artery and regulate the blood flow reaching the testis. The preganglionic parasympathetic nerves, coming from the inferior hypogastric plexus course in the wall of the vas deferens, and –via the ganglion cells located there- primarily regulate its peristaltic contractions

III./1.1.6.: Descensus testiculorum (descensus of the testes)

The anlages of the gonads (so of the primordial testes also) start to develop on the posterior abdominal wall. The testes develop on both sides of the primordial spine (at the L1-3 segment level), always staying retroperitoneally. The gubernaculum testis, a mesenchymal band rich in extracellular matrix connects the lower pole of the testis to the inguinal area, later to the labioscrotal swellings (the primordia of the scrotum). The factors controlling the testicular descent are not fully understood, but the role of androgens is quite probable. The blood supply of the developing testes is given by the testicular arteries which get always longer as the testes descend.

The wall of the celoma cavity, the developing peritoneum has a projection extending downwards, the processus vaginalis testis which moves down via the inguinal canal into the scrotum earlier, before the testis gets there. In the 2. gestational month begins the descent of testes guided by the gubernaculum, behind the processus vaginalis testis, so that the testes descend always in retroperitoneal position. The process of descent stops at the 3. fetal month at the deep inguinal ring and the testis stays there until the 7. intrauterine month. From that time (i.e. before birth in a healthy, mature fetus) the testes start again moving downwards into the scrotum, so (at the medical examination a healthy newborn baby boy normally has his testes already inside the scrotum).

Shortly after birth (until about the 18. months of extrauterine life) the lumen of the processus vaginalis testis is obliterated, its cavity is no longer connected to the peritoneal cavity and only a connective tissue bundle can be observed in front of the spermatic cord, as the remnant of processus vaginalis (vestigium processus vaginalis). The lower end of processus vaginalis, however, remains in the scrotum, containing a small serous peritoneal cavity around the testis as the tunica vaginalis testis.

When the descent of the testes fails, cryptorchidism (hidden testis) is the descriptive diagnosis. The retention of the testis can be caused by ‘mechanical’, ‘anatomical’ problems (e.g. lack of gubernaculum, adhesions) or endocrine dysfunctions (e.g. insufficient gonadotropins). The endocrine causes usually lead to bilateral retention of testes. If the testes remain in the abdominal cavity or in the inguinal canal, the problem is not only the resulting infertility, but malignant tumors (e.g. seminoma) can also frequently develop in the retained testes. For this reason, it is important to examine carefully the testes in the scrotum after birth (repeatedly, if necessary, in case of non palpable testes in warmer environment as well since cold causes reversible retraction of the testes).

In case of examination of inguinal hernia it is also important to check whether the testes have arrived already in the scrotum or not -to avoid to misdiagnose the inguinally retained testis as inguinal "hernia".

If the lumen of processus vaginalis fails to obliterate after birth and its cavity remains still connected with the peritoneal cavity, there is a an increased risk for inguinal hernia (indirect hernia). If the connection is lost, but the cavity remains cyst or series of cysts may develop along the course of processus vaginalis. The wall of these cysts can produce fluid (hydrocele testis, hydrocele of spermatic cord).