Monday, October 1, 2012

Internal Arterial Distribution of the testis


As the testicular artery leaves the inguinal canal and approaches the upper end of the testis, if it has not done so at a higher level, it divides into two tortuous main branches, an outer branch, the internal testicular artery and an inner branch, the inferior testicular artery.

Surrounded by the pampiniform plexus, the tortuosity of the testicular arteries increases as they approach the testis. This arrangement may be considered a heat-exchange system to cool the arterial blood.

The inner, larger branches from the inferior testicular artery run between the testis and the epididymal body. They enter the posterior border of the testis, medial to the epididymis, at several points. The outer branches, arising from the internal testicular artery, pass obliquely through the tunica albuginea to enter the tunica vasculosa.

These vessels form an aggregation, appearing as a vascular hilum, that requires ligation during intracapsular orchiectomy after the testicular substance has been separated from the interior of the tunica albuginea. The distribution of these vessels under the tunica albuginea is not uniform; the superior medial and superior lateral portion of the tunic have the fewest major branches, whereas the superior anterior and all inferior aspects have the most.

Considerable variation is found in the branching and distribution of the vessels, but typically, the outer and inner arterial branches ramify in the tunica vasculosa over the lateral and the medial curvatures of the testis as the coiled centripetal arteries. These run toward the rete and, in turn, put out branches that reverse the course and return as centrifugal arteries. Both sets of arteries divide further in the testicular parenchyma and end as intertubular arterioles. The capillaries that arise from the arterioles enter the interstitial tissue and are separated from the germinal and supporting cells by a basement membrane that constitutes the “blood-testis barrier.”

An understanding of the centripetal distribution of the arteries is important during testicular biopsy, when they will be most liable to section by an incision on the anterolateral aspect of the testis; a major superficial artery will most likely be encountered on the anterior, lateral, and medial aspect of the lower pole and is least likely on the medial and lateral aspect of the upper pole. An anchoring suture in the lower
pole may similarly jeopardize the blood supply.

The rete testis is meagerly supplied by small vessels from the mediastinum of the testis and from small centripetal branches of the testicular artery.

The tunica albuginea has its own system of capillary networks at several levels that are not related to the vasculature of the testis proper but arise independently from branches of the testicular artery, from vessels supplying the rete and from branches of the epididymal artery.

The epididymal artery, a single branch of the testicular artery, arises at variable distances proximal to the epididymis. It supplies the head and body of the epididymis through one or more capital arteries. The tail is vascularized by a complex arrangement of vessels involving the
epididymal, vasal, and testicular arteries, with supplementation
from the cremasteric artery. This system provides an extensive anastomotic loop among these vessels that is important when the testicular artery must be divided to achieve scrotal placement of the testis. It has been determined that the sum of the diameters of the cremasteric and vasal arteries is equal to the diameter of the testicular artery in a third of cases, but in another third the cremasteric artery is not anastomotic.

The vasal artery along its course on the vas provides small branches, some of which may join the testicular artery in the cord just above the epididymis. The artery branches to join the posterior epididymal arteries to form an epididymaldeferential loop. After ligation of the testicular artery during orchiopexy, the testis becomes dependent on the anastomosis of this loop with the terminal part or distal branches of the testicular artery, a connection that may or may not be adequate to support the testis. Anastomoses between the testicular and vasal arteries do not follow a regular pattern, which may account for the variable results of long-loop orchiopexy.

The cremasteric artery runs outside of the internal spermatic fascia and so supplies an extremely limited amount of blood to the structures within. However, some terminal branches may reach the lower pole of the testis and anastomose with the epididymal-deferential loop, with a terminal branch of the testicular artery or with branches of the epididymal artery. In cryptorchidism, the artery is usually too short to be mobilized and must be sacrificed.

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