Open Fontanelle in Small Breed Puppies

By Catherine Barnette, DVM

What is an open fontanelle?

Open fontanelles are soft spots in the skull, or gaps between the skull’s growth plates. They can be normal in young puppies, especially small breeds, but they typically close or harden by 9-12 weeks of age. In some breeds, such as Chihuahuas and Miniature Dachshunds, it is not uncommon for open fontanelles to persist beyond 12 weeks of age. In fact, open fontanelles in Chihuahuas are referred to as “moleras” and they are considered to be part of the breed standard, along with the classic dome-shaped skull.

What causes an open fontanelle?

Open fontanelles are a normal finding in very young puppies. As normal puppies mature, the growth plates in their skull fuse together and the soft spots known as open fontanelles gradually reduce in size until they no longer exist. Persistent open fontanelles, however, are a common genetic condition that is seen in some small dog breeds, including Chihuahuas, Miniature Dachshunds, Pomeranians, Shih Tzus, Yorkshire Terriers, Maltese, Lhasa Apsos, and Pekingese. In these dogs, persistent open fontanelles are caused by genetic abnormalities in normal developmental skull closure. The growth plates in these dogs simply fail to fuse in a normal manner, leaving a persistent soft spot in the skull.

"...fontanelles gradually reduce in size until they no longer exist."

In some cases, open fontanelles may be caused by an underlying brain condition, such as hydrocephalus. The term hydrocephalus means “water on the brain.” In hydrocephalus, cerebrospinal fluid (CSF) accumulates within the brain, causing the brain to swell. This swelling places pressure on the skull, which can contribute to open fontanelles, a dome-shaped skull, and other abnormalities. Fortunately, most cases of open fontanelles are genetic and are not associated with hydrocephalus.

How is an open fontanelle diagnosed?

During a physical examination, your veterinarian will palpate your puppy’s skull (along with the rest of the body) to assess for the presence of open fontanelles and other skull abnormalities. If an open fontanelle is noted in a young puppy, its presence will be documented and the open fontanelle will be monitored at future visits for signs of closure. Open fontanelles that persist beyond three to four months of age are diagnosed as persistent open fontanelles.

Depending on your dog’s skull abnormalities, your veterinarian may recommend imaging (such as radiographs or ultrasound) to further evaluate your dog’s skull structure. In most cases, however, a diagnosis of persistent open fontanelles is made solely on the basis of a physical examination.

Should I be concerned about my dog’s open fontanelle?

Open fontanelles do not typically cause problems for affected dogs. In theory, the soft spot in the skull could make your puppy more susceptible to brain injury in the event of a blow to the head. However, this is uncommon and dogs with persistent open fontanelles typically live normal, healthy lives.

"Open fontanelles do not typically cause problems for affected dogs."

Open fontanelles are only a true cause for concern when they are associated with hydrocephalus. If your veterinarian suspects that your puppy has hydrocephalus, you may be referred to a veterinary neurologist for a thorough evaluation. Signs of hydrocephalus may include behavioral changes, trouble walking, circling, and the presence of a large, dome-shaped skull. In the absence of neurologic signs or other skull abnormalities, your puppy’s open fontanelles are unlikely to be related to hydrocephalus.

Is there a treatment for open fontanelles?

There is no treatment for open fontanelles. However, dogs that have persistent open fontanelles should not be bred. Because open fontanelles are a genetic condition, breeding dogs with open fontanelles will create more dogs with this issue.

If your puppy is diagnosed with hydrocephalus, treatment may be indicated. Treatment may include a combination of medication and surgery, depending on your neurologist’s recommendations.

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