Association of Extreme Brachycephaly With Persistent Fontanelles in Adult Chihuahuas

A recent study investigated the relationship between cranial morphology and persistent fontanelles (PFs) in adult Chihuahuas, a condition where the soft spots on the skull do not close as expected. Despite being common in Chihuahuas, the link between cranial shape and PFs had not been previously explored. The study aimed to understand how cranial features, including skull shape and bodyweight, might influence the presence of PFs in this breed.

Fifty client-owned Chihuahuas were examined in a retrospective cross-sectional study using computed tomography (CT) scans. Researchers measured various aspects of the dogs' skulls, including cranial base lengths, cranial height, width, and length, along with craniofacial angles. They also calculated ratios such as cranial height to cranial base lengths and cranial index (CrI), which helped assess the relationship between cranial morphology and PF characteristics like total PF area and the number of sutures affected by PFs.

The results showed that Chihuahuas with higher cranial height-to-base length ratios and higher CrI values had larger PF areas and more sutures affected by PFs. These findings suggest that more extreme brachycephaly—characterized by a higher CrI—is associated with a greater likelihood of PFs. Additionally, the study found that lower bodyweight in these dogs was associated with more pronounced brachycephalic traits. Specifically, Chihuahuas with a higher CrI tended to weigh less, highlighting that smaller body size correlates with more extreme cranial features.

This study provides valuable insight into how cranial structure, particularly extreme brachycephaly, is linked to persistent fontanelles in Chihuahuas. These findings could aid in understanding the breed's unique cranial development and may have implications for the management of PFs in affected dogs.