In most boys and men the testis is covered on its front and sides by the visceral layer of the tunica vaginalis, but its posterior surface is not so covered, and the posterior surface of the testis is therefore in direct contact with, and fused to, the layers of the posterior scrotum. Being fused to the scrotum in this way, the testis cannot twist around (Fig. 6.2). However, in some boys and men, the entire surface of the testis, together with a length of the spermatic cord, is covered with the visceral layer of the tunica vaginalis (Fig. 6.3). In these individuals the testis hangs
126 J. REYNARD AND H. HASHIM
Figure 6^ The posterior" surface of the testis is fused to the posterior" scrotum.
6. SCROTAL AND GENITAL EMERGENCIES
tunica vaginalis covering the entire testis and spermatic cord
visceral layer of
Figure 6.3. The entire surface of the testis together with a length of the spermatic cord, is covered with the visceral layer of the tunica vaginalis. This is the bell clapper, and it predisposes to intravaginal torsion of the testis and epididymis.
like the clapper of a bell within the scrotum. It is therefore free to rotate within the scrotum. This is called an intravaginal torsion, i.e., it occurs between the two layers of the tunica vaginalis.
Attached to the testis are so-called testicular appendages. These are vestigial and are derived from embryological structures. The appendix testis (also known as a hydatid of Morgagni) is a remnant of the mullerian duct (in the female fetus this develops into the fallopian tubes and upper part of the vagina). In 80% of individuals it is pedunculated (Rolnick et al. 1968) (i.e., it is on a stalk) and is therefore prone to torsion, which can cause pain (mimicking that of a testicular torsion).
The epididymis, vas deferens, and seminal vesicles are derived from the mesonephric (wolffian) duct. An appendix epididymis, not surprisingly, is a derivative of the wolffian duct (more specifically a remnant of a cranial mesonephric tubule) and it is almost always pedunculated. Like an appendix testis, the appendix epididymis may twist and cause scrotal pain.