Hydrocele is an abnormal accumulation of excess fluid in the membranes surrounding the testicles, resulting in swelling of the scrotum. Normally, there is 0.5 -1 ml of fluid between the testis and these membranes to ensure the lubrication of the testis, while in hydrocele, this amount of fluid can reach volumes of 100-200 ml and sometimes even more.

Hydrocele occurs in about 1 percent of adult men and usually over the age of 40. In adult men and older people, hydrocele may occur due to trauma to the scrotum, inflammatory diseases of the testis and its appendages, testicular tumors, varicocele surgeries and after radiotherapy. Unilateral hydrocele occurs in more than 70 percent of kidney transplant patients. Testicular torsion (sudden rotation of the testis) may cause reactive hydrocele in 20 percent of patients and may mask testicular torsion that requires immediate intervention