An open fontanelle is a soft area, present on the top of the skull.  It remains in the incompletely ossified (bone tissue not completely formed) skull of a developing puppy.  This condition occurs in human infants and is commonly called a “soft spot”.The skull is actually made up of several separate bone plates that become fused together during embryonic development.  These bones start out very small and separated.  They gradually grow around the brain and encase it as they meet and fuse together.  Four of these bones meet up at the center top of the skull with this center being the last open space to fill in with bone tissue.  This space is known as a fontanelle.  This space usually fills in slowly after the birth of the pup.  The size and frequency of open fontanelles varies with breeds (common in small breeds and brachycephalic –“flat-faced”- breeds) and the genetics of individuals (an inherited condition).

Open fontanelles, if excessively large, can create two possible problems.  This soft area leaves the brain unprotected by bone and can be a place for a brain injury to occur.  The other potential problem is hydrocephalus, also known as “water-on-the-brain”.  Hydrocephalus is an abnormal accumulation of fluid in the brain cavities causing neurologic problems.  Large open fontanelles are occasionally, but not always, associated with hydrocephalus.  For these reasons, large open fontanelles can create concern for the future health of the pup.