title: Congenital vertebral malformations in dogs: Prevalence of C7 vertebra homeotic transformation in multiple dog breeds, phenotypic characterisation of vertebral malformations in the Pug dog and evaluation of radiography as a screening method for detection and classification
Creators: name: Brocal de la Corte, Jose Maria
Publisher: name: University of Glasgow
Year: 2019
Subjects: subject: C7 vertebra homeotic transformation, transitional vertebrae, vertebral malformations, canine, pug, radiography, screening, classification, computed tomography.

description: Congenital vertebral malformations (CVM) can be associated with neurological deficits and are common in some brachycephalic dogs like the French bulldog, the English bulldog and the Pug dog. A genetic predisposition has been suggested and some predisposing genes have already been identified. While reviewing images for another parallel study, we identified a high percentage of Pug dogs with cervical ribs. Due to a strong selection against variation in the number of cervical vertebrae in mammals, the number is almost constant at seven. This finding caught our attention and we therefore decided to describe the prevalence of cervical ribs in a large group of domestic dogs of different breeds and explore a possible relation with other CVM in the breed with the highest prevalence of cervical ribs. By phenotyping we hoped to give clues as to the underlying genetic causes. The Pug dog was more affected by cervical ribs than any other breed (46%) and was selected for further analysis. No association was found between the presence of cervical ribs and vertebral body formation defects, bifid spinous process, caudal articular process hypoplasia/aplasia and an abnormal sacrum, which may infer they have a different aetiopathogenesis. However, Pug dogs with cervical ribs were more likely to have a transitional thoraco-lumbar vertebra and a pre-sacral vertebral count of 26 (normal = 27). Our findings showed that the Pug dog may be a good naturally occurring model to further investigate the aetiology of cervical ribs, other congenital vertebral anomalies and numerical alterations. Given the genetic predisposition and possible associated neurological deficits of some CVMs, we also wanted to evaluate radiography as a screening method for congenital thoracic vertebral malformations in the French bulldog, the English bulldog and the Pug dog by comparing it with computed tomography (CT). Three observers retrospectively and independently reviewed images to detect CVMs. When identified, they were classified according to a previously published radiographic classification scheme. A CT consensus was then reached. All observers identified significantly more affected vertebrae when evaluating orthogonal radiographic views compared to lateral views alone; and more affected vertebrae with the CT consensus compared to orthogonal radiographic views. Given most dogs had more than one CVM, the number of dogs classified as being CVM free was not significantly different between CT and radiography. Significantly more midline closure defects were also identified with CT compared to radiography. Malformations classified as symmetrical or ventral hypoplasias on radiography were frequently classified as ventral and medial aplasias on CT images. Our results supported that CT is better than radiography for classification of CVMs. These findings are of importance for designing screening schemes of congenital vertebral malformations that could help selective breeding programs based on phenotype and future studies.