Hydrocele

Normally, there is a small hole/ defect in the lower part of the abdominal wall in the fetus during development through which the testicle (which forms in the tummy) in boys descends into the scrotum. This hole closes off some time before a baby is born. If this fails to close, fluid or solid contents from within the tummy can descend into the scrotum and can cause a hydrocele
When the hole is small enough to permit the passage of only fluid, the fluid accumulates in a ‘sac’ within the scrotum and causes scrotal enlargement.