Unilateral vs. Bilateral Varicocele: What’s the Difference?

A varicocele can affect one side of the scrotum or both. A unilateral varicocele occurs on a single side, while a bilateral varicocele affects both. While having enlarged veins on both sides sounds concerning, the physical location alone does not tell the whole story about your reproductive health or daily comfort.

Below, we explain how unilateral and bilateral varicoceles differ, how each relates to fertility, how doctors evaluate them, and when treatment is actually necessary.

A varicocele is an enlargement of the veins inside the scrotum — the pampiniform plexus — that help drain blood from the testicles. These veins typically form gradually and are most frequently discovered during or after puberty.

Because of the natural pathway of male blood vessels, varicoceles occur far more often on the left side. Many men never experience symptoms, learning they have one only during a routine exam, while others notice a dull scrotal ache, a feeling of heaviness, or visible, twisted veins.

A unilateral varicocele affects only one side of the scrotum — most commonly the left. The left testicular vein joins the renal vein at a direct angle, creating higher resting pressure that makes the left side more susceptible to blood pooling.

Depending on vein size and blood accumulation, a single-sided varicocele can present with: a persistent, dull ache or feeling of dragging that worsens late in the day; a visible or feelable mass («bag of worms»); testicular size discrepancy on the affected side; decreased sperm production or quality.

A bilateral varicocele means enlarged veins are present on both the left and right sides of the scrotum. Anatomically, this simply indicates that the venous drainage pathways on both sides have developed dilated vessels. This condition is usually identified during a physical exam, a routine fertility workup, or a scrotal ultrasound.

The physical distribution of the veins is only one aspect of the diagnosis. For both unilateral and bilateral varicoceles, clinical care decisions rely on physical examination findings, semen analysis results, testicular volume, and individual patient goals — not simply how many sides are involved.

When evaluating male fertility, urologists prioritize functional measurements — specifically semen analysis results and testicular volume — rather than how many sides are involved. Key parameters include sperm count, motility, morphology, testicular health, and how long a couple has been attempting to conceive. Because sperm production naturally fluctuates, urologists typically review multiple tests over time.

Can a unilateral varicocele also cause infertility? Yes. Even when present on only one side, blood pooling can raise overall scrotal temperature and increase oxidative stress, impairing sperm production in both testicles. However, many men with a single-sided varicocele have normal semen parameters and father children without medical intervention.

Evaluating a suspected unilateral or bilateral varicocele follows a simple process: physical examination — the primary step, with the patient standing and sometimes performing a Valsalva maneuver to make enlarged veins easier to feel; semen analysis — recommended when family planning is a goal, measuring sperm count, movement, and shape; scrotal ultrasound — used if the exam is inconclusive or other structures need checking (routine ultrasound solely to find tiny, non-palpable varicoceles is generally not advised); testicular assessment — measuring volume to verify both testicles are developing normally.

Treatment is personalized, and not every varicocele requires a procedure. Per urological guidelines, repair is generally considered when the varicocele is physically palpable, the couple has documented difficulty conceiving, and the male partner has abnormal semen parameters. Treatment may also be considered for adolescents showing testicular shrinkage or adults with persistent, unmanageable pain. Small varicoceles seen only on ultrasound and not felt by hand are generally not treated.

A varicocele diagnosed on one side can sometimes be found on the other side later — usually not a brand-new issue, but a previously subtle varicocele becoming more noticeable. However, a unilateral varicocele does not inevitably spread to both sides; new swelling, changes in appearance, or worsening pain warrant evaluation. What actually determines clinical severity isn’t location, but specific indicators: vein grade (visible, palpable at rest, or only felt on Valsalva), semen parameters, testicular size, and comfort level.

Consider scheduling an evaluation if: you have been diagnosed with a varicocele and want to discuss family planning; you and your partner have been trying to conceive for 12 months without success; you have an abnormal semen analysis result; you experience persistent scrotal aching, heaviness, or discomfort; you notice a distinct size difference between your testicles; you notice new or enlarging swollen veins in your scrotum.

Is a bilateral varicocele worse than a unilateral one? Not necessarily. Clinical grade, sperm health, testicular size, and symptoms determine overall severity — not simply whether one or both sides are involved.

Do I automatically need surgery if I have a varicocele? No. The decision depends on clinical findings, symptoms, testicular development, semen parameters, and the patient’s fertility goals.

Can a varicocele affect both testicles? Yes — when enlarged veins develop on both sides, it is classified as bilateral.

Can a varicocele cause infertility without causing pain? Yes. Pain and fertility operate through different mechanisms; a completely painless varicocele can still affect sperm production, which is why a semen analysis is crucial for evaluation.