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.
