Causes of Testicular Torsion
Testicular torsion is caused by twisting of the spermatic cord, which results in compromised testicular blood flow, and the primary anatomic risk factor is the "bell-clapper" deformity, an abnormal fixation of the testis within the tunica vaginalis. 1
Primary Anatomic Cause
The bell-clapper deformity is the key anatomic defect that predisposes to testicular torsion. 1 This abnormality allows the testis to rotate freely within the tunica vaginalis, like a bell clapper inside a bell. MRI can identify this deformity with 83% sensitivity by demonstrating hyperintense T2 signal between the posterior aspect of the epididymis and the scrotal wall, described as a "split sign." 2
Mechanism of Torsion
The rotation of the vascular pedicle of the testis impedes blood flow to the testis and scrotal contents. 3 This can occur either:
- Intravaginal torsion (most common in adolescents and adults): The testis twists within the tunica vaginalis, typically associated with bell-clapper deformity 1
- Extravaginal torsion (occurs in neonates): The entire testis and tunica vaginalis twist together on the spermatic cord, often occurring prenatally or perinatally 4
Age-Related Patterns
Testicular torsion has a bimodal age distribution with distinct peaks: 5
- Neonatal period: Extravaginal torsion accounts for approximately 10% of pediatric testicular torsion cases 4
- Postpubertal boys (12-18 years): Peak incidence with an estimated yearly rate of 2.9 to 3.8 per 100,000 boys under 18 years 5
- Adults over 35 years: Testicular torsion is rare in this population 5
Degree of Torsion and Vascular Compromise
The severity of ischemic injury depends on: 1
- Degree of arterial compression: Complete torsion >450 degrees results in absent arterial and venous flow 2
- Partial torsion: Venous obstruction precedes arterial occlusion due to thinner vessel walls and lower pressure, which can present with diminished arterial velocity and decreased diastolic flow 2
- Time to intervention: A critical 6-8 hour window exists before permanent ischemic damage occurs 5
Clinical Pitfall
The cause of testicular torsion in adolescents is fundamentally unknown beyond the anatomic predisposition of bell-clapper deformity. 6 While the anatomic defect is usually present, the specific trigger for torsion at any given moment remains unclear. Up to one-half of patients report previous similar episodes, suggesting intermittent partial torsion may occur before complete torsion. 1