Most men who notice a small lump on or behind a testicle worry about cancer first, and most of the time the worry is unfounded. A spermatocele, also called an epididymal cyst, is a benign fluid-filled sac on the epididymis that contains old sperm cells and clear or milky fluid. Spermatoceles are common, usually painless, and rarely require treatment, though they can grow large enough to cause discomfort and occasionally need to be removed.
What a Spermatocele Is
The epididymis is a coiled tube along the back of each testicle that stores and matures sperm. A spermatocele forms when a small portion of the epididymal tubule dilates or pinches off, accumulating fluid. Most spermatoceles arise in the head of the epididymis, the upper portion adjacent to the top of the testicle. According to the Urology Care Foundation, spermatoceles are detected in roughly 30 percent of men on careful scrotal ultrasound, though most are too small to feel.
The exact cause is not well understood. Theories include obstruction of an epididymal duct, prior inflammation, and minor trauma. Spermatoceles do not appear to increase the risk of testicular cancer, infertility, or other serious conditions.
Symptoms
Most spermatoceles are asymptomatic and discovered incidentally during a routine exam, a testicular self exam, or scrotal ultrasound performed for other reasons. When symptoms occur, they include a palpable smooth round bump on the back or top of the testicle, a sensation of heaviness or fullness, mild aching with prolonged standing or activity, and rarely tenderness on palpation.
Spermatoceles range from a few millimeters to several centimeters. Larger ones can be felt as a separate lump distinct from the testicle, often described as feeling like a small grape or marble above or behind the testicle. They tend to grow slowly if at all.
How It Differs From Other Scrotal Findings
Several other conditions cause scrotal lumps and need to be distinguished from spermatocele. Hydroceles surround the testicle rather than sitting separately on the epididymis. Varicoceles feel like a “bag of worms” of dilated veins above the testicle. Epididymitis presents with pain, swelling, and often fever. Testicular tumors arise within the testicle itself, not on the epididymis, and feel firm and fixed.
Distinguishing these reliably requires examination and often ultrasound. The medical conditions library covers related scrotal conditions in greater detail.
How a Spermatocele Is Diagnosed
Physical examination identifies most clinically significant spermatoceles. A clinician palpates a smooth, well-defined, fluid-filled mass on the epididymis, separate from the testicle. The mass usually transilluminates with a flashlight, glowing as light passes through the fluid.
Scrotal ultrasound is the imaging study of choice. It confirms the cystic nature, distinguishes spermatocele from solid masses, and assesses the testicle for unrelated abnormalities. According to Mayo Clinic, ultrasound reliably differentiates spermatocele, hydrocele, varicocele, and tumor in nearly all cases.
Treatment
Observation
Most spermatoceles need no treatment. Asymptomatic cases are followed clinically with periodic self-exams and physician visits. Many remain stable or grow only minimally over years.
Spermatocelectomy
Surgical removal is reserved for spermatoceles causing significant pain, discomfort with daily activities, or large size that bothers the patient cosmetically. The procedure is performed as an outpatient under local, spinal, or general anesthesia. The cyst is dissected from the epididymis through a small scrotal incision. Recovery takes 1 to 2 weeks for most activities.
One important consideration is fertility. Spermatocelectomy can damage the epididymis, potentially impairing sperm transport on the affected side. For men who want to preserve fertility, particularly those who have not completed their families, the decision to operate is approached cautiously. Some clinicians defer surgery until childbearing is complete or use minimally invasive approaches when feasible. The male infertility guide covers related considerations.
Aspiration and Sclerotherapy
Needle aspiration of spermatocele fluid is occasionally performed but has high recurrence rates. Sclerotherapy improves durability but is not standard in most US practice and may damage the epididymis.
When to See a Doctor
Any new scrotal lump, change in an existing lump, persistent pain, sudden size change, or signs of infection warrants evaluation. Even when self-examination strongly suggests a spermatocele, a baseline ultrasound is reasonable to confirm the diagnosis and document the testicle’s appearance.
When to seek emergency care: Call 911 or go to the nearest emergency room if you experience sudden severe testicular pain (testicular torsion is a 6-hour surgical emergency), acute scrotal swelling with redness or fever, or severe scrotal trauma. A spermatocele itself is not an emergency.
Frequently Asked Questions
Can a spermatocele turn into cancer?
Spermatoceles are benign and do not become cancerous. They do not increase the risk of testicular cancer. However, any new lump deserves evaluation to confirm the diagnosis.
Will a spermatocele affect my fertility?
Spermatoceles themselves do not typically cause infertility. The greater fertility risk often comes from spermatocelectomy surgery, which can damage the epididymis on the affected side. Men concerned about fertility should discuss timing carefully with their urologist.
Do spermatoceles come back after surgery?
Recurrence rates after spermatocelectomy are low (under 10 percent in most series). Aspiration alone has substantially higher recurrence.
How fast do spermatoceles grow?
Most grow slowly, often over years. Rapid growth is uncommon and warrants ultrasound to confirm the diagnosis and rule out other processes.
The Bottom Line
A spermatocele is among the most common benign scrotal findings and rarely needs treatment. The first step when a new lump is felt is examination and scrotal ultrasound to confirm the diagnosis and rule out conditions that mimic it. When a spermatocele does become bothersome enough to consider surgery, the conversation includes fertility implications, since spermatocelectomy can affect epididymal function on the operated side. Most men with spermatoceles live with them indefinitely without consequence.