Fontanelles Part 1-Do you know your sutures?

JVIM 2021

March 02, 2025

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

Background
Chihuahuas often display persistent fontanelles (PFs), particularly bregmatic fontanelles, due to their cranial anatomy. This study aimed to describe the prevalence, distribution, and clinical relevance of PFs, especially in relation to Chiari-like malformation (CM) and syringomyelia (SM), conditions known to affect this breed.

Methods
The study examined 50 Chihuahuas (2012–2015) using magnetic resonance imaging (MRI) and computed tomography (CT). Dogs were classified into groups based on the presence or absence of CM/SM-related clinical signs. PFs were identified as full-thickness bone deficiencies at cranial sutures, and their size and number were evaluated. Statistical analyses compared PF distribution and area between groups.

Results
-Prevalence: PFs were present in 92% of the dogs, with an average of 2.8 PFs per dog.

-Distribution: Most PFs were at dorsal cranial sutures (52%), followed by caudal (36%) and lateral (12%) surfaces.

-Clinical correlation: Dogs with CM/SM-related clinical signs had significantly more PFs and larger total PF areas than unaffected dogs.

-Key Findings: 48% of PFs occurred at non-standard locations, challenging assumptions that PFs are limited to specific cranial sites.

Limitations
The study was restricted to Chihuahuas from a single geographical region, potentially limiting generalizability. Imaging limitations occasionally made it difficult to distinguish true PFs from thin bone areas. Additionally, PF etiology (congenital vs. acquired) could not be definitively established.

Conclusions
PFs are highly prevalent in Chihuahuas and are more numerous and larger in those with CM/SM-related clinical signs. The findings suggest PFs may share pathophysiological mechanisms with CM/SM, challenging the notion that PFs are clinically irrelevant. Reevaluation of breeding standards emphasizing traits linked to PFs is recommended.

A-C, Dorsal, lateral, and caudal volume-rendering technique computed tomography images (window level 500, window width 3500) of a Chihuahua skull showing the cranial sutures evaluated in this study. Numbers 1 to 5 mark dorsal cranial sutures, 6 to 8 lateral cranial sutures, and 9 to 12 caudal cranial sutures evaluated: 1a (left), 1b (right): frontonasal, frontomaxillar, and frontolacrimal sutures; 2: interfrontal suture; 3a-b: frontoparietal suture, 4: sagittal suture, 5a-b: parietointerparietal suture, 6: left frontopalatine and sphenofrontal sutures, 7: intersection of left frontoparietal, sphenofrontal, and sphenoparietal sutures (resembling sphenoid fontanelle in children); 8: left sphenoparietal and squamous sutures; 9a-b: intersection of squamous, occipitoparietal, and occipitosquamous sutures (resembling mastoid fontanelle in children); 10a-b: occipitoparietal suture, 11: junction between occipital and interparietal bones (not a true suture); 12a-b: occipitosquamous suture

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