Fontanelles part 3.

Association of Extreme Brachycephaly With Persistent Fontanelles in Adult Chihuahuas

Elina Rautala, Tarja S. Jokinen, Junnu Leikola, Mirja Ruohoniemi, Clare Rusbridge, Jouni J. T. Junnila, Anna-Mariam Kiviranta

Background
Persistent fontanelles (PFs) are common in adult Chihuahuas, yet their relationship with cranial morphology remains unclear. Extreme brachycephaly, characterized by a short and wide skull, has been linked to conditions such as Chiari-like malformation and syringomyelia. This study aimed to investigate whether extreme brachycephaly is associated with the presence and severity of PFs in Chihuahuas and to determine if body weight correlates with cranial morphology.

Methods
A retrospective cross-sectional study was conducted on 50 client-owned Chihuahuas using computed tomography (CT) images. Craniometric measurements, including cranial base length, cranial height, width, and craniofacial angles, were assessed. The total PF area and the number of cranial sutures affected by PFs were quantified and analyzed for associations with cranial morphology. Additionally, relationships between craniometric indices and body weight were evaluated.

Results
Dogs with more extreme brachycephaly, as indicated by a higher cranial index (CrI), exhibited a significantly larger PF area and a greater number of cranial sutures affected by PFs. Specifically, a higher cranial height-to-cranial base length ratio and increased cranial width were associated with more severe PFs. Additionally, lower body weight was correlated with a more extreme brachycephalic skull shape.

Limitations
The study was limited to a single breed and a relatively small sample size, which may restrict the generalizability of findings. Additionally, the retrospective design may introduce selection bias, and the lack of longitudinal data prevents assessment of how PFs develop over time. The study did not evaluate genetic influences on skull morphology.

Conclusions
Findings suggest that extreme brachycephaly is strongly associated with the presence and severity of PFs in adult Chihuahuas. Furthermore, smaller body weight is linked to a more extreme cranial conformation, which may predispose dogs to PFs. These results highlight the need for further investigation into the clinical implications of PFs and the potential impact of selective breeding on cranial morphology in Chihuahuas.

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