An epididymal cyst is a fluid-filled sac that forms in the epididymis, the coiled tube sitting behind each testicle that stores and transports sperm. These cysts are benign, surprisingly common, and in most cases cause no symptoms at all. About 14% of males who undergo scrotal ultrasound have one, and the rate climbs with age: more than 35% of boys older than 15 show cysts on imaging. Most people discover them by accident during an unrelated exam.
Where It Forms and What’s Inside
The epididymis is a long, tightly coiled tube attached to the back of the testicle. Sperm mature here before traveling onward. An epididymal cyst develops when a small pocket within this structure fills with clear, straw-colored fluid that contains no sperm. The cyst is lined with a true layer of cells and may originate from the lymphatic ducts near the epididymis or from tubules that have dilated due to inflammation or a congenital blockage.
Most cysts stay small, just a few millimeters across, though they can occasionally grow to about 5 cm in diameter. They can appear on one side or both. In a study of 861 men undergoing fertility evaluations, 19% had a cyst on the right side, 22% on the left, and 13% had cysts on both sides, with a median size of 4 mm.
Epididymal Cyst vs. Spermatocele
The two terms are sometimes used interchangeably, but they aren’t identical. A simple epididymal cyst contains clear fluid with no sperm cells. A spermatocele holds a dilute, milky suspension of mostly immotile sperm. Chemically, the sperm-free fluid from either type is similar: lower in protein, sugar, and cholesterol than blood, but higher in testosterone and chloride. From the outside, both feel the same on examination, and distinguishing them usually requires ultrasound or, occasionally, analysis of the fluid itself. The practical difference for patients is minimal, since both are benign and managed the same way.
What It Feels Like
Most epididymal cysts produce no symptoms whatsoever. When there are signs, the most common is a small, smooth, painless lump felt separate from the testicle itself. The lump typically moves freely under the skin, isn’t stuck to surrounding tissue, and isn’t tender to touch. If a doctor shines a light through the scrotum (a transillumination test), the cyst lights up because it’s filled with clear fluid, which can sometimes cause confusion with a hydrocele, a different type of fluid collection.
Scrotal pain is minimal or absent in the vast majority of cases. Occasionally a larger cyst can create a feeling of heaviness or mild discomfort, particularly during physical activity. A cyst that suddenly becomes painful, red, or swollen may signal a separate issue like torsion or infection, not a complication of the cyst itself.
How It’s Diagnosed
Physical examination can raise suspicion, but scrotal ultrasound is the standard tool for confirming the diagnosis. On ultrasound, a simple epididymal cyst appears as a well-defined, round, fluid-filled structure with thin walls and no internal debris. This appearance is distinct enough to rule out more concerning possibilities like a solid mass. Many cysts are found incidentally when ultrasound is ordered for an unrelated reason, such as pain, swelling, or a fertility workup.
Effect on Fertility
One of the most common concerns men have when told they have an epididymal cyst is whether it could affect their ability to have children. The evidence is reassuring. A 2024 study of 861 men presenting for fertility evaluation found no statistically significant difference in sperm volume, concentration, motility, morphology, or total motile sperm count between men with and without cysts. Cyst size and whether it appeared on one or both sides made no difference either. Separate research confirmed that epididymal cysts were not associated with infertility after adjusting for other known risk factors like age, testicular volume, and varicocele.
If you’re found to have a cyst during a fertility workup, it’s very unlikely to be the cause of any difficulty conceiving.
When Treatment Is Needed
The default approach for an epididymal cyst is simply to leave it alone. Since these cysts are benign and don’t affect fertility or testicular function, observation is appropriate for the vast majority of cases, especially when the cyst is small and painless.
Treatment becomes a consideration when a cyst causes persistent pain, grows large enough to be physically bothersome, or creates significant anxiety despite reassurance. The main surgical option is excision, sometimes called spermatocelectomy or epididymectomy depending on how much tissue is removed. In one series, 92% of men who had surgery specifically for an epididymal cyst reported high satisfaction with the outcome, a notably better result than for men who had surgery for chronic epididymal pain from other causes (43% satisfaction).
What Surgery and Recovery Look Like
Surgical removal is typically an outpatient procedure, meaning you go home the same day. Expect some discomfort for the first few days afterward, managed with standard painkillers. Most guidance recommends taking 10 to 14 days off work and avoiding strenuous exercise or heavy lifting during that window to allow the wound to heal. Sexual activity is best postponed for about 10 days or until soreness resolves.
Complications are possible but generally not severe. A population-based study of 161 patients undergoing scrotal surgery for cysts and hydroceles found an overall complication rate of about 19%. The most common issues were infection or abscess formation (9.3%) and persistent swelling suggesting the problem wasn’t fully resolved (9.3%). Chronic pain after surgery was rare, occurring in less than 1% of patients. These numbers apply to scrotal surgery broadly, not just cyst removal, so individual outcomes may vary.
Known Risk Factors
The exact cause of most epididymal cysts remains unclear. They can arise from congenital blockages in the tiny tubules of the epididymis, or from inflammation that causes a section of the duct to dilate and fill with fluid. Age is the most consistent factor: cysts become more common as boys move through puberty and into adulthood. There is some evidence linking fetal exposure to diethylstilbestrol (DES), a synthetic estrogen once prescribed during pregnancy, to a higher prevalence of epididymal cysts in adult men, though DES exposure is now rare since the drug was discontinued decades ago. No strong genetic predisposition has been established for the common, isolated cyst.