1 in 5 men affected by 'bag of worms' testicle condition, doctor warns

Most men who discover they have a varicocele find out by accident. A routine physical exam, an ultrasound for something else, or a fertility workup triggers the diagnosis – and in many cases, the man had no idea anything was wrong. The condition often causes no pain. There’s no lump anyone could feel from the outside. Yet its effects on the internal environment of the testicle can be considerable.

A varicocele is an enlargement of the veins inside the scrotum, specifically a network of small blood vessels called the pampiniform plexus. According to Johns Hopkins Medicine, these vessels become abnormally dilated when the valves within the testicular veins stop working properly, allowing blood to pool rather than flow efficiently back toward the heart. The result is a cluster of widened, twisted veins wrapped around the testicle – which is where the “bag of worms” description comes from. Patient.info notes that a large varicocele is sometimes described as looking and feeling exactly like that in the scrotum.

The condition is more common than most people realize. A 2026 study in the World Journal of Men’s Health found that varicocele occurs in approximately 15% of males and is associated with 35 – 44% of primary male infertility cases. That prevalence figure – roughly 1 in 5 men – places varicocele among the most widespread urological conditions in existence. Professor Suks Minhas, a consultant urologist and head of specialty in urology at Imperial College Healthcare NHS Trust and centre director of the European Academy of Andrology at Imperial College London, has flagged varicocele as a key area of concern in male reproductive health – one where earlier identification can meaningfully change outcomes.

Why the Left Side Is Almost Always Affected First

Varicocele has long been recognized as a condition that can affect male fertility, and while it’s the most common surgically correctable cause of male infertility, not all varicoceles require treatment. One of the condition’s defining features is its strong left-side bias. Current European and American guidelines recommend diagnosing and grading varicocele based on comprehensive medical history, physical examination, and ultrasound in special circumstances. Grading runs from subclinical – not visible or palpable but detectable by ultrasound – through to Grade III, where the varicocele is visibly apparent.

The anatomical reason for its left-side dominance comes down to basic plumbing. A 2025 study published in the World Journal of Men’s Health found that the left gonadal vein inserts into the left renal vein at a nearly perpendicular angle, generating increased hydrostatic pressure – the physical force of blood pressing against vein walls. That geometry makes it harder for blood to drain efficiently on the left side, so the veins dilate over time. The right testicular vein, by contrast, drains more directly into the inferior vena cava at a less obstructed angle. As a result, roughly 80% to 90% of varicocele cases occur on the left side.

Varicoceles most commonly form during puberty – specifically, according to UCLA Health, during the period when the testicles are experiencing rapid growth and require significantly increased blood flow, putting the venous drainage system under new demand it wasn’t previously handling.

What Varicocele Actually Does to Sperm

The central problem with varicocele isn’t the vein itself – it’s the temperature. The testis functions optimally at around 2 to 3 degrees below body temperature. Pooling blood raises the local temperature inside the scrotum, disrupting the carefully maintained cool environment that sperm production depends on. According to Cleveland Clinic, this warmer blood can affect the testicle’s ability to make sperm and testosterone.

The damage doesn’t stop at temperature. Varicocele can reduce male fertility potential through oxidative stress mechanisms: excessive reactive oxygen species overwhelm the sperm’s defenses, damaging sperm chromatin. Sperm DNA fragmentation, in the form of DNA strand breaks, is commonly found in the ejaculates of men with varicocele and fertility issues. In practical terms, this means a man’s sperm count can look normal on paper while the genetic material inside the sperm is significantly compromised – a factor that standard semen analysis doesn’t routinely test for.

The 2026 World Journal of Men’s Health study also found that the effects of varicocele on fertility can include decreased sperm production and quality, low testosterone levels, decreased testicular size, and elevated sperm DNA fragmentation. Testicular atrophy – gradual shrinking of the affected testicle – can also occur in more established cases, and is one of the signs clinicians look for during physical examination.

The prevalence data among men seeking fertility help is striking. Varicocele is present in up to 44% of the subfertile male population and in up to 80% of men with secondary infertility – meaning men who have fathered a child before but are now struggling to conceive again. Male infertility accounts for nearly half of all couple infertility cases worldwide, and among the potentially correctable causes, varicocele remains the most common.

The Symptoms You Might – or Might Not – Notice

A 2025 retrospective study published in CVIR Endovascular found that only 2% to 10% of men with varicocele report experiencing pain, which means the vast majority carry the condition silently. When symptoms do appear, they tend to be subtle and easy to attribute to something else. Cleveland Clinic describes them as including dull testicular pain or aching in the scrotum, swelling, and shrinking in the testicles. Some men report a sensation of heaviness in the affected testicle, especially after standing or physical exertion for extended periods.

Clinical presentations of varicocele can overlap with other conditions – including swollen veins in the scrotum, testicular atrophy, and low testosterone – and that overlap means varicocele is often diagnosed only once a man presents with fertility concerns rather than pain. That diagnostic lag matters, because longer-duration varicoceles may cause more cumulative damage to sperm-producing tissue.

The physical sign doctors look for during a genital exam is the characteristic texture of dilated veins, which in larger varicoceles can be detected by palpation, particularly when the patient performs a Valsalva maneuver – a forced exhalation against a closed airway that increases abdominal pressure and makes the veins more prominent. A scrotal ultrasound with Doppler imaging confirms the diagnosis and grades its severity.

Varicocele Fertility: Who Actually Needs Treatment

It’s estimated that 80% of men with varicocele are fertile, making the association between varicocele and decreased semen quality controversial in fertile males. The condition does not automatically mean infertility. Many men with varicoceles father children without any intervention.

Treatment is typically considered when varicocele and fertility concerns appear together. Treatment is indicated in clinical varicoceles of grades II – III and in cases of testicular pain where other causes have been excluded. For fertility issues, varicocele therapy is recommended for infertile couples where semen parameters are abnormal, no gynecological factors are present, and the female partner has a preserved ovarian reserve.

The standard surgical approach is microsurgical varicocelectomy – tying off or blocking the affected veins. The microsurgical, subinguinal approach is considered the gold standard because of its effectiveness and low complication rate. A 2025 meta-analysis found that varicocelectomy significantly improves clinical pregnancy and live birth rates in infertile patients, though it doesn’t reduce miscarriage risk. A randomized controlled trial comparing surgery to no surgery in infertile men with varicoceles found a pregnancy rate of 44% at one year in the surgery group versus 10% in the control group. Varicocelectomy results in significant improvement in semen analysis in 60 to 80% of men.

For those who prefer to avoid open surgery, varicocele embolization – a minimally invasive radiological procedure – is becoming more common. A 15-year retrospective study published in CVIR Endovascular found a technical and clinical success rate of 96% and 93.75%, respectively.

Male infertility is often linked to broader health risks, including cardiovascular disease, which makes early diagnosis and intervention even more critical. There are many correctable causes for male infertility, and surgical techniques have allowed men to achieve paternity when previously they were unable to do so.

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What to Do Now

Because the appropriate diagnosis and management of varicoceles remain less clear in many patients, it’s important to identify clinically significant varicoceles that can actually benefit from treatment. If you’re a man who has been trying to conceive for more than 12 months without success, or who has noticed any of the symptoms described – dull scrotal ache, visible veins, a sense of heaviness in one testicle – a visit to a urologist or andrologist is the logical next step. Ask specifically about a scrotal Doppler ultrasound, which is the most accurate way to detect and grade the condition.

Semen analysis remains the first-line test for male fertility evaluation, but research from the World Journal of Men’s Health suggests that sperm DNA fragmentation testing adds important information in cases where standard parameters look normal but conception hasn’t occurred. If a varicocele is confirmed, the decision to treat depends on its grade, your semen parameters, your partner’s fertility status, and how long you’ve been trying. Not every varicocele needs surgery – but the ones that are impacting fertility are among the most treatable causes of male infertility that exist. A structural problem with a known fix deserves a clinical conversation, not a wait-and-see approach that runs on for years.

Disclaimer: This information is not intended to be a substitute for professional medical advice, diagnosis, or treatment and is for information only. Always seek the advice of your physician or another qualified health provider with any questions about your medical condition and/or current medication. Do not disregard professional medical advice or delay seeking advice or treatment because of something you have read here.

AI Disclaimer: This article was created with the assistance of AI tools and reviewed by a human editor.

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