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Relationship of brachycephalic features, skulls and hydrocephalus

Schmidt MJ, Kampschulte M, Enderlein S, Gorgas D, Lang J, et al. The Relationship between Brachycephalic Head Features in Modern Persian Cats and Dysmorphologies of the Skull and Internal Hydrocephalus. J Vet Intern Med. 2017 Aug 20.

In modern times, the extreme exaggeration of certain traits in many breed for dogs and cats has become common. This trend, commonly called “ultra-typing” has raised many concerns for the health of these animals. Commonly discussed issues include the facial conformation of pugs and bulldogs or hip dysplasia in German Shepherds. Similar issues have arisen recently in feline medicine, especially in the Persian and related breeds. These breeds are called “brachycephalic”, a term referring to the very short muzzle and flattened face characteristic of the breeds. This brachycephalic trait is known to associated with respiratory difficulty, respiratory infections, ocular disease, and dental malocclusion.

While the Persian breed has existed for centuries, it is only in the last 100 years that its facial conformation has become more extreme. The modern breed standard for a Persian cat describes extremely round head with great breadth and a “high nose-leather”. The forehead, nose, and chin are supposed to be in vertical alignment when viewed from the side, and the transition from nasal to frontal bone (break) is supposed to be centered between the eyes”. This description is commonly known as a “Peke-Face” Persian, for its resemblance to a Pekinese dog. The more traditional Persian appearance has become known as a “Doll-Face”.

Many breeders and veterinarians have observed a correlation between “Peke Faced” Persians and the condition Internal Hydrocephalus. This disease involves enlargement of the fluid-filled ventricular system of the brain resulting in compression of normal brain tissue. In dogs, there is a known correlation between brachycephalic breeds and hydrocephalus, leading to the assumption that this may occur in cats as well.

The purpose of this paper was to investigate if there is a correlation between degree of brachycephaly and ventricular enlargement, and to further evaluate the specific abnormalities of the skull and brain associated with brachycephaly.

The study was designed as a cross sectional evaluation of Persian cats in Germany. Persians from breeding clubs were recruited for MRI and CT evaluation of the head. Retrospective analysis of CTs from multiple teaching hospitals were also performed. MRI and CT studies of 10 Domestic Shorthaired cats from archives were analyzed as controls. Cats with any bony or brain lesions that may have distorted the skull or ventricular system were excluded. Determination of doll vs peke face traits were made by CT alignment of the eyes with the nose.

A series of CT and MRI measurements were made to establish a craniometric analysis (breakdown of various skull bone dimensions) and volumetric measurements of brain and ventricular volume, cranial capacity, and grey and white matter volumes.

35 Persians and 10 DSH cats were included retrospectively, and 57 prospectively. Of the 92 cats, 45 had a “doll face” morphology while the remaining 47 were “Peke Faced”. Five  “Peke Faced” kittens from three litters presented for severe ataxia resulting in inability to stand, peripheral nystagmus, head tremors, abnormal breathing patterns, obtundation, and sustained aimless screaming. These kittens were euthanized due to severity of clinical signs and were evaluated post-mortem.

Significant bony changes were discovered in the “Peke Faced” group, full discussion of which is beyond the depth of this summary. In brief, “Peke Face” cats had grossly reduced cranial length with increased width and height, rounded and domed skulls, and lack of a sagittal crest. Many cats demonstrated deviations of the maxilla, loss of nasal turbinate’s, loss of nasal sinus and alterations of even loss of the nasal bone, flat orbits, and retrograde conchae. Several cats had ossification defects.

MRI demonstrated that “Peke Faced” Persians displace nasal turbinates into the cranial cavity. The osseous changes desrbined above were associated with separation of the olfactory bulbs, rounding of the brain, rounding and displacement of the corpus callosum, and other changes. 38 of these cats experienced herniation of the cerebellum through the foramen magnum, and in 5 kittens it was >50% herniated. Herniation was also seen in 12 “doll face” Persians, but none of the DSH cats. Ventricular enlargement was present in 29 Peke faces and no Doll Faces.

The traits of ventricular enlargement and cerebellar herniation were statistically associated with Peke-Face morphology. Peke faces also had statistically higher ventricular volumes and lower white matter to grey matter ratios.

This study showed that selection for “Peke Face” conformation has a negative effect on skull and brain morphology. Reduction of the facial bones is correlated with deformation of the cranial vault and corresponding brain lesions. The authors postulate that the signs seen in feline specimens bear a strong resemblance to the humane syndrome known as coronal craniosynostosis.

While a group of described cats were severely enough affected to require euthanasia, many of the cats with ventricular enlargement showed no significant clinical signs. It is postulated by the authors that these cats may experience chronic white matter loss as described in dogs, leading to cognitive impairment. Future research into this is required.

While this study successfully established correlation between skull conformation and brain anomalies, it did not demonstrate causation, and it remains possible that a confounding trait exists linking the two. Further research into the embryology, anatomic, and physiologic factors determining hydrocephaly should be undertaken, especially given the recent identification of candidate genes linked to these traits.

While cross-sectional in nature, this study demonstrates the wide range of brain abnormalities that occur in extremely brachycephalic cats. The clinical ramifications of these changes are extremely wide ranging, but always deleterious to the animal’s quality of life. The data presented here adds to the weight of evidence against the continued breeding of “Peke-Faced” Persians and indeed any severely brachycephalic breed. The respiratory, ocular, and dental complications associated with this condition are well described, and significant neurologic sequalae can now be added to that list. (MRK)

See also:
Farnworth MJ, Chen R, Packer RMA, et al. Flat feline faces: Is brachycephaly associated with respiratory abnormalities in the domestic cat (Felis catus)? PLoS ONE 2016;11:e0161777.