Testicular torsion refers to the torsion of the spermatic cord structures and subsequent loss of the blood supply to the ipsilateral testicle. This is a urological emergency; early diagnosis and treatment are vital to saving the testicle and preserving future fertility. The rate of testicular viability decreases significantly after 6 hours from onset of symptoms. 

Testicular torsion is primarily a disease of adolescents and neonates. It is the most common cause of testicular loss in these age groups. However, torsion may occasionally occur in men 40-50 years old.

Surgical treatment may prevent further ischemic damage to the testis. Rarely, observation is appropriate, depending on the pathology. Diagnosis of testicular torsion is clinical, and diagnostic testing should not delay treatment.

Testicular torsion is caused by twisting of the spermatic cord and the blood supply to the testicle (see the image below). With mature attachments, the tunica vaginalis is attached securely to the posterior lateral aspect of the testicle, and, within it, the spermatic cord is not very mobile. If the attachment of the tunica vaginalis to the testicle is inappropriately high, the spermatic cord can rotate within it, which can lead to intravaginal torsion. This defect is referred to as the bell clapper deformity. This occurs in about 17% of males and is bilateral in 40%.

Intravaginal torsion most commonly occurs in adolescents. It is thought that the increased weight of the testicle after puberty, as well as sudden contraction of the cremasteric muscles (which inserts in a spiral fashion into the spermatic cord), is the impetus for acute torsion.

By contrast, neonates more often have extravaginal torsion. This occurs because the tunica vaginalis is not yet secured to the gubernaculum and, therefore, the spermatic cord, as well as the tunica vaginalis, undergo torsion as a unit. Extravaginal torsion is not associated with bell clapper deformity. This can occur up to months prior to birth and, therefore, is managed differently depending on presentation. Of course, neonates can have intravaginal torsion and this should be managed in the same manner as adolescents.

Testicular torsion is associated with testicular malignancy, especially in adults; one study found a 64% association of testicular torsion with testicular malignancy. This is thought to be secondary to a relative increase in the broadness of the affected testicle compared with its blood supply.  However, in a review of 32 patients who had been diagnosed with testicular torsion, testicular cancer was found in 2 of the 20 patients who had undergone orchiectomy, a rate of 6.4%.