Varicoceles are enlarged veins within the scrotum, similar to varicose veins in the leg. They affect about 15% of all men, but that number jumps to 35% among men with primary infertility and as high as 80% among men with secondary infertility (those who previously fathered a child but can no longer conceive). Several widely tested statements about varicoceles are grounded in well-established clinical evidence, and understanding which facts hold up helps separate reliable knowledge from common misconceptions.
Left-Sided Predominance Is Real
One of the most consistently true statements about varicoceles is that they occur on the left side 80% to 90% of the time. This isn’t random. The left testicular vein drains into the left renal vein at a steep angle, creating more hydraulic resistance than the right side, where the vein empties directly into the larger vena cava. The junction between the left testicular vein and renal vein also lacks effective one-way valves, so blood flows backward more easily. On top of that, the left renal vein can get compressed between two major blood vessels in the abdomen (the aorta and the superior mesenteric artery), further raising pressure. These three anatomical factors combine to make left-sided varicoceles far more common than right-sided or bilateral ones.
Most Varicoceles Cause No Symptoms
The majority of men with a varicocele never know they have one. When symptoms do occur, the hallmark is a dull, aching discomfort that worsens with standing or physical activity and improves when lying down. Some men describe a dragging or heavy sensation in the scrotum. The classic physical finding is a cluster of dilated veins that feels like a “bag of worms” above the testicle. Pain tends to build over the course of the day rather than striking suddenly.
Varicoceles Are Graded on a Three-Point Scale
Clinicians use a grading system introduced in 1970 that remains the standard today:
- Grade I: Only detectable by touch when the patient bears down (Valsalva maneuver) while standing.
- Grade II: Detectable by touch at rest while standing, without needing the Valsalva maneuver.
- Grade III: Visible through the scrotal skin without any special maneuvers.
Subclinical varicoceles, those only found on ultrasound, fall below Grade I and are generally not considered clinically significant.
They Are a Leading Cause of Reversible Male Infertility
This is one of the most important true statements about varicoceles: they represent the most common correctable cause of male infertility. The damage comes from two main mechanisms. First, pooled venous blood raises scrotal temperature above the narrow range sperm production requires. Second, the stagnant blood flow triggers a cascade of oxidative stress, generating reactive molecules that directly damage sperm cell membranes and DNA.
These effects show up across every major semen parameter. Men with varicoceles tend to have lower sperm counts, reduced motility, abnormal sperm shape, and higher rates of DNA fragmentation in sperm cells. The DNA damage is particularly significant because it reduces the ability of sperm to fertilize an egg even during assisted reproduction procedures. Notably, about 15% of men with varicoceles have completely normal semen analyses yet still experience infertility, suggesting the damage can be subtle.
Testicular Shrinkage Signals Ongoing Damage
Varicoceles can cause the affected testicle to lose volume over time. In one large study of over 600 men with left-sided varicoceles, 50% had measurable shrinkage of the left testicle (a volume decrease of 3 ml or more). This shrinkage is considered a sign of persistent testicular damage and is one of the key reasons treatment is recommended, particularly in adolescents. For younger patients, a volume difference of 2 to 3 ml, or roughly a 10% to 20% size discrepancy compared to the unaffected side, is the threshold most specialists use when deciding whether to intervene.
Surgical Repair Improves Sperm Quality
Varicocele repair, most commonly performed as a microsurgical procedure through a small incision near the groin, produces measurable improvements in semen quality. A meta-analysis found that after repair, sperm concentration rose by nearly 10 million per milliliter on average, progressive motility improved by about 9 percentage points, and DNA fragmentation dropped significantly. These improvements appear quickly: sperm counts increase by roughly 53% within three months of surgery, and no further gains are seen beyond that point. Men considering repair should plan for a semen analysis around the three-month mark to assess results.
The microsurgical technique has the lowest recurrence rate at just over 1%, compared to about 13% for catheter-based embolization (a procedure where a radiologist blocks the vein from the inside). For men with varicoceles on both sides, surgery is the clear winner because embolization failure rates climb to 19% for bilateral procedures. For a left-sided varicocele alone, the two approaches have comparable success rates of roughly 3%.
Not Every Varicocele Needs Treatment
Because varicoceles are so common in the general population, the presence of one alone does not automatically call for intervention. Treatment is typically considered when a varicocele is associated with abnormal semen parameters, testicular pain that affects daily life, or progressive shrinkage of the affected testicle. In adolescents, the decision is more nuanced because fertility cannot yet be tested directly. Most specialists monitor younger patients with periodic ultrasound measurements and semen analysis when age-appropriate, reserving surgery for those who show clear testicular volume loss or declining sperm parameters over time.
Bilateral varicoceles exist in a meaningful subset of men and are associated with worse fertility outcomes than unilateral ones. When bilateral repair is needed, microsurgical correction is preferred because it maintains low failure rates on both sides simultaneously.