A spermatocele is a fluid-filled cyst that forms in the epididymis, the small coiled tube that sits on top of each testicle and carries sperm. These cysts are benign, meaning they are not cancerous and do not become cancerous. Most spermatoceles are small, painless, and discovered by accident during a physical exam or an ultrasound done for another reason.
Where Spermatoceles Form
The epididymis wraps along the back and top of each testicle. It has three sections: the head (at the top), the body (along the back), and the tail (at the bottom). Spermatoceles almost always arise from the head of the epididymis, which means they sit above or just behind the upper pole of the testicle. Because of this position, you can usually feel a spermatocele as a separate lump distinct from the testicle itself.
Inside the cyst is a dilute fluid containing mostly immotile (non-swimming) sperm cells. Analysis of spermatocele fluid shows it is chemically different from blood: it contains less protein, less glucose, and less cholesterol than serum, but higher levels of testosterone and chloride. It also lacks the specialized secretion products normally found in a healthy epididymis, which suggests the cyst is somewhat walled off from the active transport system around it.
What Causes Them
The exact cause remains unclear. The leading theory is that a blockage somewhere in the tiny tubules of the epididymis traps fluid and sperm, gradually forming a cyst. In animal studies, researchers have found that clumps of germ cells can plug the ducts downstream, causing upstream dilation. Other hypotheses include small aneurysm-like expansions of the epididymal tube itself. One interesting finding: up to 80% of spermatoceles contain motile sperm, which suggests the tubes above the cyst are still open and functioning normally even when a blockage exists below.
Prior injury, infection, or inflammation of the epididymis may play a role in some cases, but many spermatoceles appear in men with no history of scrotal problems at all.
How They Feel
Most spermatoceles cause no symptoms. Small ones, under a centimeter, are often undetectable by touch. Larger spermatoceles can feel like a smooth, round, movable lump just above or behind the testicle. They typically feel distinct from the testicle and may shift slightly when pressed.
When a spermatocele does cause discomfort, it is usually a sense of heaviness or dull aching in the affected side of the scrotum. Sharp pain is uncommon. Some men notice the lump only because of a feeling of fullness, especially when sitting for long periods. Very large spermatoceles can become noticeable enough to cause self-consciousness or physical inconvenience, which is often what prompts someone to seek evaluation.
How Doctors Identify a Spermatocele
A physical exam is the starting point. During palpation, the doctor checks whether the lump is attached to the testicle or separate from it, and whether it feels solid or fluid-filled. Spermatoceles feel smooth, round, and distinct from the testicle.
Transillumination is a quick bedside test where a light is held against the scrotum. Because a spermatocele is filled with clear or slightly cloudy fluid, the light passes through it, making the mass glow. Solid masses like tumors block the light. This simple step can often confirm a cyst without any imaging.
If the findings are ambiguous, an ultrasound provides a definitive picture. On ultrasound, a spermatocele appears as a well-defined, fluid-filled structure in the head of the epididymis. The main reason for ordering an ultrasound is to rule out a testicular tumor or other cause of scrotal swelling, not because the spermatocele itself is dangerous.
Spermatoceles and Fertility
A spermatocele on its own does not typically affect fertility. The cyst traps a small pool of sperm, but the testicle continues producing sperm normally, and the remaining epididymal tubes continue transporting it. Men with spermatoceles generally have normal semen analyses.
Surgery to remove a spermatocele, however, carries a small risk of damaging the epididymal tubules near the surgical site. If the epididymis is injured during the procedure, it could impair sperm transport on that side. For this reason, doctors are generally cautious about recommending surgery in younger men who plan to have children, and observation is preferred unless symptoms are significant.
When Treatment Is Needed
The default approach for a spermatocele is no treatment at all. If the cyst is small and painless, there is nothing medically necessary to do. Many men live with spermatoceles for years without any change in size or symptoms.
Treatment is considered when the spermatocele causes persistent pain, grows large enough to be bothersome, or creates significant anxiety. The options fall into two categories: aspiration with sclerotherapy and surgical removal.
Aspiration and Sclerotherapy
This is a less invasive option where a needle is used to drain the fluid from the cyst, followed by injection of a sclerosing agent (a substance that irritates the cyst lining and encourages it to seal shut). In a study of 34 patients with spermatoceles treated this way, about 74% had complete resolution after a single procedure. Those who still had fluid remaining were offered a second round, and after at most two procedures, the overall success rate reached 85% at a median follow-up of 31 months. The appeal of this approach is that it avoids a surgical incision, but the trade-off is a meaningful chance the cyst returns.
Surgical Removal
Spermatocelectomy is the definitive treatment. The surgeon makes a small incision in the scrotum and carefully dissects the cyst away from the epididymis. It is typically done as an outpatient procedure under local or general anesthesia.
Recovery generally involves a few days of soreness and swelling, with most men returning to desk work within a week and avoiding heavy lifting or vigorous activity for two to four weeks. Scrotal support (snug underwear or a jock strap) and ice packs help manage swelling in the first few days.
Complications are not rare. In one study tracking outcomes after scrotal surgeries, roughly one in three patients contacted their surgical department afterward due to unexpected swelling or pain, and about 7 to 9% required a reoperation. Patients who had their preoperative consultation with an experienced urologist had significantly fewer complications than those seen by trainees, which underscores the value of choosing a surgeon with specific experience in scrotal procedures.
Spermatocele vs. Other Scrotal Lumps
- Hydrocele: A hydrocele is a fluid collection that surrounds the testicle rather than sitting above it. It transilluminates like a spermatocele but feels different on exam because the fluid envelops the entire testicle rather than forming a distinct lump.
- Varicocele: A varicocele is a cluster of enlarged veins, usually on the left side. It often feels like a “bag of worms” and changes size when you stand versus lie down. It does not transilluminate.
- Epididymal cyst: These are nearly identical to spermatoceles in feel and location. The difference is that epididymal cysts contain clear fluid without sperm, while spermatoceles contain sperm. In practice, the distinction rarely matters because both are benign and managed the same way.
- Testicular tumor: A hard, painless lump that feels attached to the testicle itself, not separate from it. It does not transilluminate. Any firm, fixed mass within the testicle warrants urgent evaluation.