An epididymal cyst is a harmless, fluid- filled sac that forms in the epididymis (the coiled tube that runs along the back of the testis and stores sperm from the testis).
Epididymal cysts often occur in both testes and are most common in middle-aged and older men. The cysts are usually painless and need no treatment.
Occasionally, an epididymal cyst may become large and cause discomfort, or, very rarely, may become twisted and painful (a condition called torsion of an epididymal cyst), which is a medical emergency and requires surgery.