Purrplexing Brains: When Cat Cerebellums Take the Plunge

Shape of the feline cerebellum and occipital bone related to breed on MRI of 200 cats

Xander Huizing, Andy Sparkes, Ruth Dennis

Background
This study aimed to describe anatomical variations in the feline cerebellum and occipital bone using MRI, with particular focus on cerebellar crowding or herniation through the foramen magnum in neurologically normal cats. The authors hypothesized that these variations may be common and potentially associated with brachycephalic head conformation, such as in Persian cats, and could mimic pathological changes seen in diseases like Chiari-like malformation in dogs.

Methods
A retrospective review was conducted of 200 adult cats that had undergone high-field MRI scans of the brain at the Animal Health Trust between 2000 and 2013. Cats with clinical or MRI evidence of intracranial disease were excluded. Midline sagittal T2-weighted images were used to classify cerebellar shape and occipital bone morphology into predefined categories. Additionally, the intracranial cavity width-to-length ratio (ICCR) was calculated as an indirect measure of brachycephaly. Breed, age, sex, and ICCR were analyzed in relation to anatomical classifications.

Results
Forty percent of the cats displayed cerebellar crowding or herniation (category C3) without neurological signs. Persian cats showed a significantly higher prevalence of this morphology compared to several other breeds, suggesting a link with brachycephalic conformation. However, no significant correlation was found between occipital bone shape and cerebellar shape. Cats with higher ICCR, indicative of brachycephaly, were more likely to show cerebellar herniation. Occipital bone thickness varied across the population but did not correlate with breed or cerebellar morphology.

Limitations
This study lacked post-mortem confirmation of imaging findings, relied on retrospective data, and included relatively small numbers for some breeds, limiting statistical power. The ICCR, while informative, is an indirect measure of brachycephaly and may not capture all relevant cranial features.

Conclusions
Cerebellar crowding or herniation through the foramen magnum is a common anatomical variation in neurologically normal cats, particularly in brachycephalic breeds such as Persians. These findings underscore the need for careful interpretation of MRI to avoid misdiagnosing normal anatomical variants as pathological changes.

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