BLOOD SUPPLY OF THE TESTIS
The arterial supply to the testis is derived from three sources: the
internal spermatic artery, the deferential (vasal) artery, and the external
spermatic or cremasteric artery. The internal spermatic artery originates from
the abdominal aorta just below the renal artery. Embryologically, the testicles
lie opposite the second lumbar vertebra and keep the blood supply acquired
during fetal life. The internal spermatic artery joins the spermatic cord above
the internal inguinal ring and pursues a course adjacent to the pampiniform
venous plexus to the mediastinum of the testicle. The vascular arrangement
within the pampiniform plexus, with the counter-flowing artery and veins,
facilitates the exchange of heat and small molecules. For example, testosterone
passively diffuses from the veins to the artery in a concentration-limited
manner, and a loss of the temperature differential created by this system is
associated with testicular dysfunction in men with varicocele and
cryptorchidism.
Near the mediastinal testis,
the internal spermatic artery is highly coiled and branches before entering the
testis. Extensive interconnections between the internal spermatic and
deferential arteries allow maintenance of testis viability even after division
of the internal spermatic artery. The testicular arteries penetrate the tunica
albuginea and travel inferiorly along the posterior surface of the testis
within the parenchyma. Branching arteries pass anteriorly over the testicular
parenchyma. Individual arteries to the seminiferous tubules, termed centrifugal
arteries, travel within the septa that contain tubules. Centrifugal artery
branches give rise to arterioles that supply individual intertubular and
peritubular capillaries.
The deferential artery
(artery of the vas) may originate from either the inferior or superior vesical
artery (see Plate 2-6) and supplies the vas deferens and the cauda epididymis.
A third artery, the external spermatic or cremasteric artery, arises from the
inferior epigastric artery inside the internal inguinal ring, where it enters
the spermatic cord. This artery forms a network over the tunica vaginalis and
usually anastomoses with other arteries at the testicular mediastinum.
Veins within the testis are
unusual in that they do not run with the corresponding intratesticular
arteries. Small parenchymal veins empty into either the veins on the testis
surface or into a group of veins near the mediastinum testis. These two sets of
veins join with deferential veins to form the pampiniform plexus. The pampiniform
plexus consists of branches of freely anastomosing veins from (1) the anterior
(or internal) spermatic veins that emerge from the testicle and accompany the
spermatic artery to enter the vena cava; (2) the middle
deferential group that accompanies the vas deferens to pelvic veins; and (3)
the posterior or external spermatic group that follows a course along the posterior spermatic cord. The latter group empties into branches of the
superficial and deep inferior epigastric veins and the superficial and deep pudendal
veins. The middle and posterior veins provide collateral venous return of blood
from the testicles after internal spermatic vein ligation with varicocelectomy.
The right internal spermatic
vein enters the inferior vena cava obliquely below the right renal vein forming
a natural “valve” to reduce retrograde blood flow, whereas the left vein
terminates in the left renal vein at right angles, without a natural valve.
This anatomic relationship is thought to explain the fact that 90% of
varicoceles are on the left side.
With varicocele formation,
the blood flow in the internal spermatic vein is reversed, thus disturbing
venous drainage from the testis and potentially elevating scrotal temperature.
As a consequence, orchalgia and infertility can occur. In high-ligation
varicocelectomy procedures (Palomo), the internal spermatic artery and vein are
both ligated above where the deferential vessels and the external spermatic
veins exit the spermatic cord, thus affording sufficient collateral circulation
to maintain testis viability. During inguinal or subinguinal procedures, care
is needed to spare the internal spermatic artery, as collateralization may be less extensive at this anatomic level.
