Work

Cranial fontanelles and the association of bregmatic fontanelle width with cranial morphology in newborn Chihuahua and non-brachycephalic puppies

Year: 2026

Type: article

Abstract: Introduction In adult Chihuahuas, persistent fontanelles are common and have been associated with extreme brachycephaly. It is currently unknown whether persistent fontanelles are congenital bone defects or develop during cranial growth due to bone resorption. Objectives We investigated the occurrence of cranial fontanelles, cranial shape, and relative bregmatic fontanelle width in newborn Chihuahuas and non-brachycephalic puppies. Methods The study included 50 newborn puppy cadavers. Micro-computed tomography (CT) images of the cranium were used to evaluate occurrence of cranial fontanelles and to measure relative width of the bregmatic fontanelle. Histological samples of the cranium were used to confirm the presence of cranial fontanelles. CT images of the cranium were used to evaluate craniometric ratios, including two different cranial height to cranial base length ratios, cranial height to length, and cranial height to width ratios, and cranial index (CrI). The association of the relative width of the bregmatic fontanelle with craniometric ratios was examined. Results 19/19 Chihuahuas and 6/21 non-brachycephalic puppies had cranial fontanelles. All but one puppy had only one fontanelle, which was located at the bregma. The proportion of puppies having at least one cranial fontanelle was higher in Chihuahuas than in non-brachycephalic puppies ( p < 0.001). Cranial height to cranial base length ratios, cranial height to length ratio, and CrI were higher in Chihuahuas than in non-brachycephalic puppies ( p < 0.001 for each analysis). Bregmatic fontanelle was relatively wider in Chihuahuas than in non-brachycephalic puppies ( p = 0.0013) and was associated with higher cranial height to cranial base length 2 ( p = 0.022), and cranial height to length ratios ( p = 0.023). Conclusion Bregmatic fontanelle occurred more frequently in Chihuahuas than in non-brachycephalic puppies, but other cranial fontanelles were uncommon. Our findings suggest that newborn Chihuahuas differ from adult Chihuahuas in which persistent fontanelles are frequently detected. This might indicate that persistent fontanelles located outside bregma may develop during postnatal growth, with bone remodeling and resorption being one possible mechanism. Chihuahuas had brachycephalic cranium already at the time of birth. In newborn puppies, relatively wider bregmatic fontanelle was associated with a shorter and higher cranium, i.e., brachycephalic cranial shape.

Source: Frontiers in Veterinary Science

DOI: 10.3389/fvets.2026.1922844