Chihuahua Molera: The Soft Spot, Whether It Closes and When It's Hydrocephalus

If you just brought home a Chihuahua puppy and, while petting the head, found a soft gap between the bones of the skull, take a breath: that’s called a molera, and it’s so characteristic of the breed that for decades it was considered a mark of purity. But it’s also true that the word hydrocephalus comes up in any search on the subject, and that not every vet knows Chihuahuas well.

This article separates the two: what the molera is, why your dog has one, what to do about it and, above all, which signs actually point to a problem.

This article is for information only and is not a substitute for advice from your veterinarian.

What is the molera?

A puppy’s skull, like a baby’s, is made of several bones that fuse as the dog grows. The soft spot where they haven’t joined yet is the fontanelle. In Chihuahuas, that gap on top of the head is called the molera, and unlike in most breeds, in many Chihuahuas it never fully closes.

The AKC breed standard describes the Chihuahua’s head as a well-rounded “apple dome” skull, “with or without molera.” In other words, according to the people who define what a Chihuahua is, the molera is neither a fault nor a disease: it’s an accepted trait.

You feel it as a soft area, sometimes the size of a lentil and sometimes the size of a dime, in the middle of the head between the ears and slightly forward. It can be round, oval or irregular.

Why do Chihuahuas have a molera when other breeds don’t?

Because of the shape of the head. An apple head Chihuahua has a very rounded skull and a short face, and that dome leaves less room for the bones to meet and fuse. Deer head Chihuahuas, with a longer skull, have a molera less often. The difference between the two head types, and what it means for health, is in apple head vs deer head Chihuahua.

According to the Chihuahua Club of America, the breed’s official parent club in the US, probably as many Chihuahuas are born with a molera as without one. In other words: about half.

Does the molera close?

It depends on the dog. There are three scenarios, and all three are normal:

What’s worth watching isn’t whether it closes, but whether it grows. A molera that’s the same size at 6 months as it was at 3 is a stable molera. One that’s getting bigger, or a head that’s getting more and more domed, is a reason to see the vet.

Is a molera the same as hydrocephalus?

No, and this is the important part of the article.

Hydrocephalus is a buildup of cerebrospinal fluid inside the skull that puts pressure on the brain. The MSD Veterinary Manual lists it among the congenital disorders of the nervous system, and it’s true that it’s more common in toy and dome-headed breeds like the Chihuahua. It’s also true that many dogs with hydrocephalus have an open fontanelle.

But the relationship doesn’t run the other way. The Chihuahua Club of America says it in plain words: a domed head with a molera does not predispose a Chihuahua to hydrocephalus, and it cites veterinary neurologists at the University of Minnesota and Cornell who concluded that many clinically normal toy-breed dogs have open fontanelles without hydrocephalus, and that there doesn’t appear to be any relationship between the size of the fontanelle and the disease.

In short: the molera is not a symptom. The symptoms are the symptoms.

How do I know if my Chihuahua has hydrocephalus?

By behavior and appearance, not by the gap. Signs of hydrocephalus show up in puppies and usually come several at a time:

• A very domed head, oversized even for a Chihuahua, that keeps growing.
• Eyes that point down and outward (sometimes called “sunset eyes”).
• Clumsiness: falling over, bumping into furniture, misjudging distances.
• Circling or pressing the head against a wall.
• Slow learning: not responding to their name, not getting house-training despite consistent effort.
• Seizures or episodes of blank staring.
• Excessive sleepiness and little interest in play, beyond what’s normal for a puppy.

If you see one or more of these, your vet can confirm the diagnosis with an ultrasound through the molera (that’s exactly what the gap is useful for) or an MRI. Treatments exist: medication to reduce the fluid and, in selected cases, a shunt surgery. The earlier it’s diagnosed, the better.

If your puppy has a molera and none of these signs, what they have is a Chihuahua.

How do I care for a Chihuahua with a molera?

With common sense, the same as any Chihuahua. Under the molera there’s a tough membrane, not an exposed brain, so petting the head, bathing them or putting on a hoodie carries no risk. What does make sense:

1. Avoid blows to the head. No jumping off the couch or bed; stairs or a ramp solve it.
2. Watch rough play with big dogs, and small children who don’t gauge their strength.
3. Tell your vet it’s there, so they check it at every visit and note any change.
4. Never allow anyone to tap them on the head “to train them,” obvious as it sounds.
5. If you plan to breed, know that the molera is inherited, and that a very large head or a very wide molera is a reason to think twice.

Falls and jumps are also the worst enemy of the breed’s knees, so this precaution does double duty: luxating patella in Chihuahuas covers the rest.

The molera when buying a puppy

Two things to keep in mind if you’re choosing a puppy. First: a responsible breeder neither hides the molera nor uses it as a selling point. Not “this one’s purer because it has one” and not “this one’s healthier because it doesn’t.” Second: be wary of puppies sold as “teacup” or “micro,” bred to be as small as possible: that’s where hydrocephalus really is more common, along with hypoglycemia and fractures. What’s behind those labels is in teacup Chihuahua sizes, and the other health problems worth knowing before you adopt are in common Chihuahua health problems.

What to remember

• The molera is a soft spot in the skull, accepted by the breed standard and present in about half of all Chihuahuas.
• It can close, shrink or stay open for life. All three are normal.
• A molera is not hydrocephalus. Hydrocephalus is recognized by its signs: a growing head, sunset eyes, clumsiness, circling, seizures.
• Care for it by avoiding blows and jumps, and by telling your vet.

Romeo and Lorenzo are both apple heads. Lorenzo has a tiny molera you can find if you feel for it, and it hasn’t changed since he came home. Romeo, at 11, has nothing you can feel anymore. Neither of them ever needed special care for it, beyond the house rule that you get onto the furniture by the stairs.