As in a human, the dogs skull is made out of several bones, shaped like plates.These bones are first soft, just like in a human baby, and are somewhat separated from each other. Most dogs have these plates closed at birth,or will usually close when the puppy is 4-6 weeks of age, or may close slowly over three to six month period.
The plates harden as the puppy grows,fusing to each other, and closing in the brain. The plates meet in the center, on top of the skull, and this center, the fontanel (fontanelle) is the last open space to close.
It can happen, that the fontanelle never closes, therefore leaving a whole in the skull.
Prevalent are toy breeds, especially: Chihuahuas, Maltese, Pomeranians and Yorkshire Terriers. But Papillons, Phalenes are not excluded.
In Chihuahuas, the fontanel, remains unclosed and this does not harm the dog.
If you detect an open fontanell in your puppy, make sure to give him a thorough check up at 5-6 months. Consult your veterinarian, to make sure that there are no underlying birth-defects, such as Hydrocephalus.
There is no treatment for an open fontanel. Be careful,and particularly aware, as to the sensitivity of this area . Avoid touching the area due to the potential for accidentally damaging brain tissue.
However, keep in mind that many dogs with an open fontanel live normal active lives.
Dogs with an open fontanell should not be bred.