A hydrocele is a fluid-filled sac that forms around the testicle, leading to swelling in the scrotum. It is often painless and can occur in newborns or adults. In infants, hydroceles usually resolve on their own, while in adults, they may result from injury, infection, or inflammation. Diagnosis typically involves a physical examination and may include an ultrasound to confirm the presence of fluid. Treatment is usually not necessary unless the hydrocele causes discomfort or complications, in which case a surgical procedure may be performed to remove the fluid and repair the sac.