Congenital open fontanel is seen in several toy dog breeds, but most often it's seen in Chihuahuas. The fontanel is the area at the top of the skull where the bone plates merge. When babies (human and dog) are born the bony plates of the skull are usually partly soft and separated. Usually this area closes to about the size of a dime by the time the puppy is about one year old, but sometimes the bony plates never completely fuse, leaving a hole in the top of the skull that has a soft mushy feel when you touch it. The affected pup can still live a long, full and active life.
The major difficulty with owning a Chihuahua with an open fontanel is the stress for the owner - the constant concern that the spot will be damaged. The Chihuahua with an open fontanel will be as active as any Chihuahua with a closed fontanel. As long as the owner takes a few precautions most Chihuahuas do just fine. Precautions the owner should take include protecting the Chihuahua from being hit on the head, preventing situations where the Chihuahua might fall and not allowing the Chihuahua to jump from furniture, beds, etc. It is not recommended that a Chihuahua with an open fontanel be added to a family with very young children.
There is no treatment for an open fontanel. Since open fontanels are either hereditary or genetic, once a good breeder determines which parent dog carries the gene the parent dog should be retired from the breeding program and spayed or neutered. Chihuahuas with open fontanels should not be bred.
The Chihuahua's Molera