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MRI mensuration of the canine head: the effect of head conformation on the shape and dimensions of the facial and cranial regions and their components

Hussein, Aseel Kamil (2012) MRI mensuration of the canine head: the effect of head conformation on the shape and dimensions of the facial and cranial regions and their components. PhD thesis, University of Glasgow.

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Abstract

The selection for specific physical characteristics by dog breeders has resulted in the expression of undesirable phenotypes, either directly or indirectly related to the physical characteristic selected for. One conformation that was considered desirable is extreme brachycephalia, which is associated with secondary physical changes adversely affecting the airways, eyes and central nervous system. Using a large population of pet dogs having diagnostic magnetic resonance imaging (MRI) studies, I demonstrated that the most commonly used historical head phenotype indices (Stockard and Evans indices) can be determined on MR images. I furthermore conformed that olfactory bulb angulation can be used as an alternate for classification of dog into brachycephalic, mesaticephalic and dolichocephalic head shapes, with similar results to the historical indices. The advantages of olfactory bulb angulation are that it only requires a single midline MR image and inclusion of the entire nose is not required. Using the historical indices and olfactory bulb angulation I then examined the effect of increasing brachycephalia on the appearance and dimensions of the nasal and cranial cavity. I established that progressive ventral rotation of the olfactory bulb (increasing brachycephalia) resulted in an alteration in the shape and a reduction in cross-sectional area of the nasopharynx. Similarly, increasing brachycephalia resulted in a reduction in the dorsal area of the ethmoturbinates and a corresponding reduction in the midline area of the olfactory bulb, providing a potential explanation for reduced olfactory acuity in brachycephalic dogs. Finally, I examined the effect of head phenotype on the structures of the middle fossa, the 3rd ventricle, quadrigeminal cistern and interthalamic adhesion. Head phenotype had a lesser effect on these structures, while brain disease (in particular ventriculomegaly) has a substantial effect, the recognition of which I described. These results confirm the potential of olfactory bulb angulation and orientation for objectively determining head phenotype using in vivo MRI, in particular determining the degree of brachycephalia. The study also quantified the effect of brachycephalia on the nasal cavity and rostral and middle cranial fossae dimensions. The objective quantification of head phenotype provides a useful tool for selection of breeding animals to normalise extreme brachycephalia. This might reduce the incidence of the adverse effects associated with extreme brachycephalia.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: MRI, Dogs, Brain, Head phenotype, Brachycephalic, Mesaticephalic, Dolichocephalic, Olfactory bulb, Ventricular system, CSF
Subjects: S Agriculture > SF Animal culture
R Medicine > R Medicine (General)
R Medicine > RZ Other systems of medicine
R Medicine > RD Surgery
Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Veterinary Medicine
Supervisor's Name: Penderis, Prof. Jacques and Sullivan, Prof. Martin
Date of Award: 2012
Depositing User: Miss Aseel Hussein
Unique ID: glathesis:2012-3689
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 26 Oct 2012
Last Modified: 10 Dec 2012 14:09
URI: http://theses.gla.ac.uk/id/eprint/3689

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