Study links newborn Chihuahua fontanelles to skull shape
Bottom line
A new Frontiers in Veterinary Science study suggests the “soft spot” seen at the bregma in Chihuahua puppies is present from birth more often, and in relatively larger form, than in non-brachycephalic puppies, and that its width tracks with a shorter, higher, more brachycephalic skull shape. Using micro-CT and histology in 50 newborn puppy cadavers, the researchers found cranial fontanelles in all 19 Chihuahua puppies studied, versus 6 of 21 non-brachycephalic puppies, with nearly all fontanelles limited to the bregma. The authors say that differs from adult Chihuahuas, where persistent fontanelles at multiple skull sites are frequently reported, raising the possibility that some non-bregmatic defects develop later through postnatal bone remodeling rather than being fully present at birth. (frontiersin.org)
Why it matters: For veterinary professionals, the study adds developmental context to a common clinical finding in Chihuahuas and may help refine how fontanelles are discussed with pet parents. Prior work from the same research group linked persistent fontanelles in adult Chihuahuas with extreme brachycephaly and reported clinical relevance rather than treating them as uniformly incidental. This newborn study doesn’t establish clinical risk on its own, but it supports the idea that skull conformation and fontanelle biology are connected early, while also suggesting some skull defects seen later in life may not be purely congenital. (onlinelibrary.wiley.com)
What to watch: Follow-up longitudinal studies that track Chihuahua puppies over time could clarify when non-bregmatic persistent fontanelles emerge, whether they expand during growth, and how strongly they relate to later neurologic or craniocervical disease. (frontiersin.org)
Key facts
- Study type
- Comparative study
- Journal
- Frontiers in Veterinary Science
- Sample size
- 50 newborn puppy cadavers
- Breed groups
- 19 Chihuahua puppies, 21 non-brachycephalic puppies
- Main finding
- All Chihuahua puppies had cranial fontanelles, versus 6 of 21 non-brachycephalic puppies
- Fontanelle location
- Nearly all fontanelles were limited to the bregma
- Morphology link
- Bregmatic fontanelle width was associated with a shorter, higher, more brachycephalic skull shape
- Method
- Micro-CT imaging and histology
- Main limitation
- Cadaver study with no longitudinal follow-up
A newly published study in Frontiers in Veterinary Science adds an important piece to the puzzle around cranial fontanelles in Chihuahuas: the bregmatic fontanelle appears to be common at birth in the breed, and its relative width is associated with a more brachycephalic cranial shape. In the study, researchers used micro-CT imaging and histology on 50 newborn puppy cadavers and found that all 19 Chihuahua puppies had cranial fontanelles, compared with 6 of 21 non-brachycephalic puppies. Nearly every puppy with a fontanelle had only one, located at the bregma. (frontiersin.org)
That matters because the clinical conversation around Chihuahuas has long included the “molera,” or open bregmatic fontanelle, often treated as a breed-associated quirk. But earlier studies from the University of Helsinki group challenged the idea that persistent fontanelles are always incidental. In adult Chihuahuas, the same line of research has documented frequent persistent fontanelles across multiple skull sutures, and has linked greater fontanelle burden with more extreme brachycephaly, including a shorter cranial base, increased cranial doming, and a higher cranial index. (onlinelibrary.wiley.com)
The new study helps separate what is likely present at birth from what may develop later. According to the Frontiers paper, Chihuahuas had significantly higher cranial height-to-base-length ratios, higher cranial height-to-length ratios, and a higher cranial index than non-brachycephalic puppies. The bregmatic fontanelle was also relatively wider in Chihuahuas, and that greater width was associated with a shorter and higher cranium, consistent with brachycephalic morphology already being established in the neonatal period. (frontiersin.org)
Just as notable is what the researchers did not find. Although persistent fontanelles outside the bregma are frequently described in adult Chihuahuas, they were uncommon in these newborns. The authors say that gap between newborn and adult findings may indicate that non-bregmatic persistent fontanelles can arise during postnatal growth, with bone remodeling and resorption as one possible mechanism. That interpretation remains an inference rather than proof, but it is directly supported by the contrast between the neonatal Frontiers study and prior adult Chihuahua imaging studies. (frontiersin.org)
Outside the research literature, general veterinary guidance still notes that open fontanelles can be normal in very young small-breed puppies and typically close by 9 to 12 weeks of age. This study doesn’t overturn that practical message, but it does suggest Chihuahuas may follow a more breed-specific developmental pattern, especially when brachycephalic skull conformation is pronounced. (vcahospitals.com)
Why it matters: For clinicians, the study adds nuance to how fontanelles in Chihuahua puppies are interpreted and communicated. A palpable bregmatic fontanelle in a newborn Chihuahua may reflect breed-linked cranial morphology rather than, by itself, a pathologic defect. At the same time, the broader body of evidence argues against assuming all persistent fontanelles are benign in older dogs, especially when neurologic signs, pain-related behavior, ventriculomegaly, syringomyelia, or craniocervical junction abnormalities are also in the picture. The practical takeaway is not to overmedicalize a neonatal finding, but not to dismiss persistent or multiple fontanelles later in life, either. (onlinelibrary.wiley.com)
The study also has some important limits. It was based on cadaver specimens, not live longitudinal follow-up, so it cannot show which puppies would go on to retain, enlarge, or develop additional fontanelles over time. And while the sample was enough to show significant breed differences, it does not answer whether neonatal bregmatic fontanelle width predicts future neurologic disease or imaging abnormalities. (frontiersin.org)
What to watch: The next step is prospective follow-up of Chihuahua litters from birth through skull maturation, ideally pairing serial imaging with neurologic outcomes. If future studies confirm that non-bregmatic persistent fontanelles emerge postnatally and correlate with clinically meaningful disease, that could influence breeding discussions, imaging thresholds, and how veterinarians counsel pet parents about when a “soft spot” is expected, and when it deserves closer workup. (frontiersin.org)