Testicular torsion refers to the twisting of the spermatic cord, which suspends the testis within the scrotum, leading to compromised blood supply. Anatomically, testicular torsion is classified into two primary types: intravaginal and extravaginal. While both types manifest with clinically similar symptoms and often require similar emergency treatments, their underlying mechanisms of torsion differ.

Intravaginal Torsion:
This type occurs when the testis twists *within* the tunica vaginalis, the sac that surrounds the testis. It is typically associated with an anatomical variation known as the "bell-clapper" deformity, where there is inadequate attachment of the tunica vaginalis to the gubernaculum and scrotal wall, allowing the testis to freely rotate and twist its spermatic cord inside the tunica. This is the more common type, especially in adolescents and adults.

Extravaginal Torsion:
This rarer form occurs when the testis, tunica vaginalis, and spermatic cord all twist *together, outside* the tunica vaginalis. It results from a lack of fixation of the tunica vaginalis to the scrotal wall, allowing the entire testis-tunica complex to rotate at a higher level, typically above the point where the tunica vaginalis attaches. This type predominantly affects newborns and occurs prenatally or perinatally.