Morphological and Functional Implications of the Selection on Brachycephalic Features in Feline Skulls
In cats, functional implications of selective breeding and arbitrarily defined breeding aims have been poorly investigated so far. For this reason anatomical specimens of brachy-, meso- and dolichocephalic purebred cats were examined gross anatomically and morphometrically.
A total of 70 feline skulls attributed to 10 different breeds (brachy-, meso-, and dolichocephalic) was assessed to determine those factors, which are associated with change in shape of the skull, and to point out clinical relevant findings. Morphometric data (18 parameters reflecting various lengths, widths and heights) and 22 indices underwent statistical analysis (one-way ANOVA, Scheffé Test, discriminant analysis). Additionally, the lacrimal apparatus, the nasal cavity as well as the paranasal sinuses were examined by corrosion casts, plain radiographs, computed tomography and transverse sections of frozen specimens. For radiographic investigation, bony contours also were selectively marked with a 1:1 mixture of latex (KiwoplastTM; Kurt Wolf & CO) and BaSO4 (MicropaqueTM; Guerbet).
The brachycephalic feline skull is characterised by change in shape of the braincase and the nasal cavity as well. The brachycephalic braincase was shorter (p<0.05), wider and higher compared to meso- or dolichocephalic cats. Changes in proportions of the cranial cavity were accompanied by increasing convexity of the calvaria intensifying the subjective impression of a rounded head. The shorter and smaller face (p<0.05) reduced the place inside the nasal cavity. Therefore, the turbinates extended into the frontal and sphenoid sinuses, narrowing the openings between the sinuses and the nasal cavity. The turbinates were rather obliquely orientated, so the nasal meatuses had a more curved course. Additionally, the nasolacrimal duct had a more angled course in brachycephalic cats. The frontal sinus was more often irregular in shape and subdivided into compartments by bony trabeculae. In many cases, the sphenoid sinus extended into the basisphenoid bone. In general, variations of the shape of the nasal septum, intersphenoid septum and of the foramen magnum were more commonly seen in brachycephalic skulls.
The present results confirm that brachycephalic cats are at higher risk to develop disorders of vision, olfaction and of the upper airways.