SUPERFICIAL FASCIAL LAYERS
The subcutaneous scrotal and perineal fasciae originate from the superﬁcial fascia of the abdominal wall known as Scarpa fascia. This fascial layer is found deep to Camper fascia that backs the skin as a loose layer of fatty tissue. The abdominal Scarpa fascia is a true fascial layer that consists mainly of yellowy, elastic ﬁbers that form a continuous membrane across the lower abdomen. In the upper abdomen, this fascia cannot be identiﬁed as a distinct membranous structure because it blends with the general superﬁcial fascia of the upper abdomen. In the lower lateral abdominal region, Scarpa fascia is attached to the Poupart ligament, or to the fascia lata of the upper thigh just below this ligament. It passes over the external inguinal ring to continue inferiorly over the penis and scrotum into the perineum, where it fuses with the posterior inferior margin of the urogenital diaphragm. In the perineum, this fascia attaches laterally to the inferior rami of the pubis and the superior rami of the ischium and is called Colles fascia. As the fascia envelops the base of the penis, it is joined by additional ﬁbers that extend from the dorsal penis to the symphysis, thus forming the fundiform ligament. Within the scrotum, this fascia is termed dartos fascia (dartos ﬂayed), as it is reinforced by smooth muscle ﬁbers.
Thus, deep to the skin exists a continuous superﬁcial fascial plane that begins in the lower abdomen and extends inferiorly to encompass the penis, scrotum, and anterior half of the perineum. Beneath it a potential space is formed in which ﬂuids or exudates can accumulate and spread along well-deﬁned planes. The points of fascial ﬁxation, as described, lead to exudative, infectious, or extravasative processes taking on a characteristic “butterﬂy” shape of discoloration in this region. Although they can freely extend up the anterior abdominal wall to the clavicles, such processes do not normally extend beyond the inferior landmarks without penetrating this fascia.
In the scrotal midline, an inversion of the dartos fascia forms the scrotal septum, dividing the scrotal cavity into two halves. Anatomists differ as to whether a further inward extension of Colles fascia, termed the major leaf of Colles fascia, exists. It crosses the top of the scrotal cavity, thus forming a roof and separating it from the superﬁcial urogenital pouch superiorly. Urine extravasation from the bulbar urethra would not normally gain access to the scrotal cavity without rupture or penetration of this major leaf of fascia. However, this fascia may contain rows of transverse slitlike openings in some individuals, which would allow urine access to the scrotal cavity.
As the major leaf of Colles fascia nears the upper scrotal cavity, it divides near the anterior margin of the scrotum, with a portion extending inward (see Plate 2-3). This so-called deep layer passes posteriorly, deep to the bulbospongiosus muscles, whereas the major leaf of Colles fascia in the perineal region is entirely superﬁcial to the bulbospongiosus and ischiocavernosus muscles. The deep leaf of Colles fascia lying beneath the bulbospongiosus muscle, together with the superﬁcial or major layer of fascia, forms a compartment for the bulbospongiosus muscle.