SCROTAL WALL
The testicles are maintained in position within the scrotal cavity by the
structures of the spermatic cord. Each testicle and spermatic cord is invested
in six distinct tissue layers that are acquired as a result of the descent of
the gonads from the retroperitoneum into the scrotum during fetal life.
From superficial to deep, the
first layer is the scrotal skin, thin in texture, brownish in appearance and
highly distensible. It generally assumes a rugated pattern and is continuous
with the skin of the mons pubis and penis superiorly, the perineum posteriorly,
and the medial thighs laterally. Unlike these adjacent areas, the scrotal skin
contains abundant sebaceous follicles, sweat glands, sparsely distributed hair,
and a distinct median raphe that corresponds to the scrotal septum within the
scrotum and is continuous with the median raphé of the perineum.
Beneath the scrotal
epithelium is a thin, fibrous, netlike and highly vascular tissue layer that
contains elastic and smooth muscle fibers, and is termed the tunica dartos (dartos = “flayed”). This is the superficial fascia of the scrotum (Colles fascia) that
has been previously described (see Plate 2-2). It is a continuation of Scarpa
fascia of the abdomen and Colles fascia of the urogenital triangle in the perineum
(see Plates 2-2 and 2-3). The connective tissue from this layer extends inward
to form the scrotal septum, which divides the scrotum into a compartment for
each testicle.
Deep to the dartos fascia
and separated from it by loose areolar tissue is the external spermatic fascia,
a continuation of the external oblique fascia of the abdominal wall. Beneath
the external spermatic fascia is the cremasteric fascia, which is composed of a
double layer of areolar and elastic tissue that encloses a thin layer of striated
muscle. The cremasteric fascia is a continuation of the internal oblique fascia
and occasionally contains a few fibers from the transversus abdominus muscle. It
is the cremasteric fascia that is responsible for the retraction of the
testicles, protecting them from trauma and stimuli such as cold through the
cremasteric reflex. This reflex is necessary for thermoregulatory control, as
it maintains the testicles at the optimal temperature for spermatogenesis.
Deep to the cremasteric
fascia is the internal spermatic fascia that closely invests the testicles and
inner cord structures. This layer of loose connective tissue is a continuation
of the transversalis fascia that lines the abdominal and pelvic cavities.
Beneath the internal
spermatic fascia lies the tunica vaginalis. During development, the peritoneum
forms two layers that cover each testis as it descends, one anteriorly and one
posteriorly. The posterior peritoneum forms the visceral tunica vaginalis that
surrounds the testicle where it is closely adherent to the tunica albuginea of
the testicle. The outer, parietal layer of the tunica vaginalis is derived from
the peritoneum of the anterior abdomen and is adherent to the overlying internal spermatic fascia. It is separated from the visceral layer by
endothelial cells that form a small, fluid-filled space between it and the
visceral layer. It is within this potential space that hydroceles form.
Within the spermatic cord,
running along with the vas deferens, is the inferior spermatic nerve, derived
from the pelvic plexus and carrying sympathetic and parasympathetic nerve
fibers. It is believed that this nerve is the main neural regulator of
testosterone secretion in the testis.
Two remnants from fetal
development may be present in the adult scrotum and lie beneath the visceral
layer of the tunica vaginalis: (1) the appendix testis (hydatid of Morgagni) on
the upper pole of the testis and (2) the appendix epididymis (paradidymis),
attached to the head (globus major) of the epididymis. The appendix testis represents
remnants of the fallopian tube and is derived from the cranial end of the
primitive müllerian duct, whereas the appendix epididymis is a vestige of the cranial end of the mesonephric duct (see Plate
1-2).
