Why is varicocele (varicose vein of the testicle) more common on the left side?

Anatomical Reasons for Left-Sided Predominance of Varicoceles

Varicoceles occur predominantly on the left side due to the anatomical differences in venous drainage, with the left testicular vein emptying into the left renal vein at a 90-degree angle while the right testicular vein drains directly into the inferior vena cava. This fundamental anatomical difference creates hemodynamic conditions that favor left-sided varicocele development 1.

Anatomical Factors Contributing to Left-Sided Predominance

• Left testicular vein anatomy:

  • Empties into the left renal vein at a perpendicular angle
  • Longer course compared to the right side
  • Creates higher hydrostatic pressure in the upright position

• Right testicular vein anatomy:

  • Drains directly into the inferior vena cava
  • Shorter course
  • More direct drainage pattern

• Nutcracker phenomenon:

  • Compression of the left renal vein between the superior mesenteric artery and aorta
  • Creates increased pressure in the left renal vein
  • Contributes to retrograde flow into the left testicular vein 2, 3

Hemodynamic Considerations

The hemodynamic differences between left and right sides are significant and contribute to the predominance of left-sided varicoceles:

• Pressure gradients:

  • Left renocaval pressure gradient increases from 3.8 mmHg (supine) to 7.8 mmHg (upright position) 2
  • This gradient drives retrograde blood flow in the left testicular vein
  • Standing position significantly worsens the pressure differential

• Valve incompetence:

  • Congenital incompetence of valves in the left testicular vein is common 3
  • Combined with increased hydrostatic pressure, this leads to varicocele formation

Clinical Implications

Understanding the anatomical basis for left-sided predominance has important clinical implications:

• Diagnostic considerations:

  • Isolated right varicoceles are uncommon and may warrant additional investigation
  • According to AUA/ASRM guidelines, clinicians should not routinely perform abdominal imaging for isolated small or moderate right varicoceles (Expert Opinion) 4
  • However, clinical judgment suggests abdominal imaging should be considered for men with new onset or non-reducible right varicoceles, especially if large 4

• Bilateral nature of the disease:

  • Despite left-sided predominance, varicocele is often bilateral (84% of cases) 1
  • The disease typically manifests earlier and more severely on the left side due to the longer blood column

Venous Anomalies and Right-Sided Varicoceles

When right-sided varicoceles do occur, they may be associated with venous anomalies:

• Inferior vena cava anomalies:

  • Right-sided IVC with retro-aortic left renal vein
  • Azygos continuation of IVC
  • These anomalies can lead to isolated right-sided varicoceles 5

• Clinical vigilance:

  • Practitioners should be aware that isolated right-sided varicoceles may indicate underlying venous anomalies
  • These anomalies may have other clinical implications beyond varicocele formation

Understanding the anatomical basis for the left-sided predominance of varicoceles helps clinicians make appropriate diagnostic and treatment decisions, particularly when encountering the less common right-sided or bilateral presentations.