Open fontanel is seen in numerous toy dog breeds, but most often occurs in Chihuahuas. The fontanel is the area at the top of the skull where the bone plates merge. When a Chihuahua is born (like a human baby), those bony plates are usually partly soft and separated. By the time a Chihuahua is a year old, this area closes to about the size of a dime. Sometimes, these plates never fuse and leaves a hole in the top of the skull that feels mushy to the touch. This is an open fontanel. Fear not, the Chihuahua can still live a long, active and full life. You’ll just need to be extra vigilant. A Chihuahua with an open fontanel should never be hit on the head, guard against falling and prevent the Chihuahua from jumping from furniture to furniture. If a Chihuahua has an open fontanel, he should probably not live with a family that has young children.
There is not treatment for an open fontanel. This condition is hereditary and genetic. Good breeders do not continue to breed dogs with the gene.