Some puppies are born with what is called an "open fontanel.” The fontanel is the location on the top of the skull where all of the skull plates join. It is equivalent to the soft spot at the top center of a human baby's head. When puppies are born, the bony plates of the skull are somewhat soft and separated. As he grows, these bones will become more rigid and will gradually fuse together. It can take two to six months for the skull plates to fuse and the soft spot (fontanel) to close. In some pups the fontanel never closes.
In some breeds, such as the Chihuahua, this open fontanel or molera is actually desired. This means the owner has to be particularly aware as to the sensitivity of this area.
It should be noted that even if the fontanel never closes, the affected pup can still live a full, energetic and active life. The major difficulty with owning a dog with an open fontanel is the constant concern that the spot will be damaged. The dog is unaware that there is a problem and will be as rambunctious as any "normal" dog.
It is mistakenly assumed that because a Maltese has an open fontanel, he will also have hydrocephalus (water on the brain).While puppies with hydrocephalus will commonly have an open fontanel due to the swelling of the brain, this is not necessarily an indication the puppy will have hydrocephalus.