Testicular torsion can be distinguished into extravaginal and intravaginal based on the relationship of the axis of rotation of the funicle to the tunica vaginalis.

The tunica vaginalis is the serous membrane that surrounds the testicle and epididymis except posterolaterally, where it attaches to the testis at each side of the epididymis.

Fig 1: Normal tunica albuginea rappresentation

Inferiorly, tunica vaginalis is also fixed at the scrotal wall through the gubernaculum testis (scrotal ligament).

Generally, the gubernaculum testis completes its development by the third month of life.

Extravaginal torsion happens when the tunica vaginalis and its content rotate together on the axis of the spermatic cord.

Fig 2: Extravaginal testicular torsion: tunica vaginalis and its content rotate together on the axis of the spermatic cord

This is generally due to the incomplete development of anchoring systems (gubernaculum testis), which is very rare after the third month of life.

Intravaginal torsion occurs when the testis, epididymis, and spermatic cord rotate within the tunica vaginalis.

Fig 3: Intravaginal testicular torsion: the testis, epididymis, and spermatic cord rotate within the tunica vaginalis

This event generally happens in the presence of a Bell Clapper deformity where the tunica vaginalis has an abnormally high attachment to the spermatic cord and lacks attachments to the scrotal wall.

Fig 4: Bell-Clapper deformity: the tunica vaginalis has an abnormally high attachment to the spermatic cord

Furthermore, testicular torsion can be divided into two age-dependent groups: perinatal torsion (occurring prenatally or within one month of birth) and childhood torsion (older than one month).

Table 1: Scheme of testicular torsion age-dependent groups

Perinatal torsion is most of the time an extravaginal torsion, while childhood torsion is usually an intravaginal torsion.