An epididymal cyst, or spermatocele, is a fluid-filled cyst in the coiled tube above and behind each testicle, the epididymis, explains WebMD. They are usually painless, may contain dead sperm and feel like a smooth, firm lump outside the testicle. They have no effect on a man's ability to conceive a child. One possible cause is obstruction of the epididymal ducts, the tubes that carry sperm from the testicles.
Epididymal cysts often cause no symptoms, but when they do, they can include a general swelling of the scrotum, WebMD says. Occasionally, an epididymal cyst causes redness, pain or a feeling of pressure at the base of the penis. Rarely, an epididymal cyst can restrict blood supply to the penis and require a spermatocelectomy, an operation to remove the cyst. A spermatocelectomy may also be used in cases where the epididymal cyst causes pain or if it grows in size over time. Most of the time, however, an epididymal cyst requires no treatment, and many go away naturally.
Diagnosis of an epididymal cyst requires a transillumination test, where a doctor shines a light through the scrotum to examine any unusual lumps, explains WebMD. Epididymal cysts are filled with fluid, and light shines through them, whereas solid masses, such as cancerous tumors, are opaque to light.