Persistent fontanelles in Chihuahuas. Part II: Association with craniocervical junction abnormalities, syringomyelia, and ventricular volume

Background: Persistent fontanelles (PFs) are, in Chihuahuas, almost ubiquitous. Furthermore, Chihuahuas are predisposed to other craniomorphological abnormalities, including syringomyelia (SM), ventriculomegaly, and craniocervical junction (CCJ) overcrowding resulting in neural tissue deviation. It is, however, undetermined if PFs are more common in dogs with these structural abnormalities, and their etiology is unknown.

Hypothesis/objectives: Persistent fontanelles are more numerous and larger in Chihuahuas with low body weight, older age, SM, dilated fourth ventricle, ventriculomegaly, and CCJ overcrowding.

Animals: Fifty client-owned Chihuahuas.

Methods: Cross-sectional study evaluating the association of both the number of cranial sutures affected by PFs (NAS) and total fontanelle area (TFA), based on computed tomography with SM, fourth ventricle dilatation, lateral ventricle volume, and extent of neural tissue compression at the CCJ based on magnetic resonance images.

Results: The NASs was higher and TFA larger in dogs with low body weight (NAS: P = .007; 95% confidence interval [CI] = 0.384-0.861; TFA: P = .002; 95% CI = -1.91 to -0.478), larger lateral ventricles (NAS: P ≤ .001; 95% CI = 1.04-1.15; TFA: P ≤ .001; 95% CI = 0.099-0.363), and more severe neural tissue compression at the CCJ (NAS: P ≤ .001; 95% CI = 1.26-2.06; TFA: P = .03; 95% CI = 0.066-1.13). Similarly, dogs with SM (NAS: P = .004; 95% CI = 1.26-3.32; TFA: mean ± SD, 130 ± 217 mm² ; P = .05) had higher NAS and larger TFA than did dogs without SM (43.7 ± 61.0 mm² ). Age was not associated with NAS (P = .81; 95% CI = 0.989-1.01) or TFA (P = .33; 95% CI = -0.269 to 0.092).

Conclusions and clinical importance: Persistent fontanelles are associated with small size, SM, ventriculomegaly, and CCJ overcrowding.