Fontanelles part 2-Are they as incidental as we think?

JVIM 2021

March 03, 2025

Anna-Mariam Kiviranta, Clare Rusbridge, Anu K. Lappalainen, Jouni J. T. Junnila, Tarja S. Jokinen

Background
This study investigates the association between persistent fontanelles (PFs) and craniocervical junction (CCJ) abnormalities, syringomyelia (SM), and ventricular volume in Chihuahuas. PFs are common in this breed and may co-occur with conditions like SM and ventriculomegaly, but the nature of these relationships remains unclear.

Methods
A cross-sectional analysis of 50 Chihuahuas was conducted using computed tomography (CT) to assess PFs and magnetic resonance imaging (MRI) to evaluate SM, ventricular dimensions, and CCJ abnormalities. Measurements included the number of affected cranial sutures (NAS) and total fontanelle area (TFA). Statistical analyses explored correlations between PF characteristics, body size, and structural brain and CCJ abnormalities.

Results

-PF Prevalence and Size: Dogs with smaller body weight had significantly more and larger PFs.

-Association with SM and Ventricular Volume: Higher NAS and larger TFA correlated with SM presence and increased lateral ventricular volume. However, maximum syrinx width was not associated with PF metrics.

-CCJ Overcrowding: Dogs with CCJ overcrowding had higher NAS and larger TFA, suggesting a shared pathophysiological link with other cranial abnormalities.

Limitations
The study's limitations include a single geographical population, subjectivity in fourth ventricle dilatation grading, and restricted imaging of the spinal cord to cervical regions, potentially missing associations with caudal syrinx width. Lateral ventricular volumes were approximated rather than directly measured.

Conclusions
PFs are significantly associated with SM, ventriculomegaly, and CCJ overcrowding in Chihuahuas, suggesting shared developmental or pathophysiological mechanisms. These findings challenge the belief that PFs are clinically insignificant and raise ethical concerns about breeding practices that favor extremely small body sizes. Further studies are needed to explore whether PFs result from congenital or acquired factors or a combination of both.

A Chihuahua (weight 3.5 kg) with multiple persistent fontanelles, ventriculomegaly, syringomyelia, and craniocervical junction overcrowding. A-C, Volume-rendering-technique computed tomography image of a Chihuahua skull in dorsal (A), left lateral (B), and caudal (C) views, showing multiple, persistent fontanelles (total fontanelle area of 214 mm2). D, T1-weighted transverse brain magnetic resonance image of the same dog in (A-C), showing moderate ventriculomegaly (ventricular volume 2.9 mm3). E, T2-weighted sagittal brain and spinal cord (C1-C5) magnetic resonance image of the same dog in (A-C), showing concomitant medullary elevation and dorsal spinal cord compression at C1-C2 (sum index 0.68) and syringomyelia at C2-C3. F, T1-weighted, transverse spinal cord magnetic resonance image of the same dog from (A-C), showing an asymmetrical syringomyelia (maximum width 4.7 mm) at the level of C3 and extending into the left dorsal horn

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