The tunnel should close after the testicles move through it. In some boys, the tunnel doesn't completely close. This can cause swelling because the fluid which cushions the intestines can drain into the scrotum. Sometimes the swelling can increase and decrease as a child strains or cries. If the tunnel is large enough to allow the intestines to move down toward the scrotum, the boy has a hernia.
Hydroceles are more common in boys who are born prematurely.
If the hydrocele is small it is usually safe to watch it. Many of them will go away as the boy grows. If the hydrocele is large or if it is still present as a boy gets older it needs to be fixed. The best treatment for a hydrocele is a surgery to close the tunnel draining into the scrotum. For that reason we recommend checking both sides at the same time.