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).