Congenital bipartite atlas with hypodactyly in a dog: clinical, radiographic and CT findings

Four Unusual Cases of Congenital Forelimb Malformations in Dogs

Simple Summary

Congenital limb defects are sporadically encountered in dogs during normal clinical practice. Literature concerning their diagnosis and management in canine species is poor. Sometimes, the diagnosis and description of congenital limb abnormalities are complicated by the concurrent presence of different malformations in the same limb and the lack of widely accepted classification schemes. In order to improve the knowledge about congenital limb anomalies in dogs, this report describes the clinical and radiographic findings in four dogs affected by unusual congenital forelimb defects, underlying also the importance of reviewing current terminology.

Abstract

Four dogs were presented with thoracic limb deformity. After clinical and radiographic examinations, a diagnosis of congenital malformations was performed for each of them. In one case, a deformity involving both the radial and ulnar side of the distal limb was observed. Based on clinical and radiological evaluations, a diagnosis of postaxial terminal longitudinal ulnar hemimelia was performed. The term ectrodactyly was used to refer different malformations characterized by skin and soft tissue separation of the distal forelimb observed in two dogs. Simple complete uncomplicated syndactyly of the right forelimb, and complex incomplete uncomplicated syndactyly of the left forelimb were diagnosed in the fourth case. To the authors’ knowledge, ectrodactyly and simple complete uncomplicated syndactyly are very uncommon anomalies in companion animals and have been rarely documented. Moreover, postaxial terminal longitudinal ulnar hemimelia has still not been reported in dogs.

Thoracic Vertebral Canal Stenosis Associated with Vertebral Arch Anomalies in Small Brachycephalic Screw-Tail Dog Breeds

OBJECTIVE

 The aim of this study was to describe clinical and imaging features of thoracic vertebral canal stenosis secondary to the hypertrophy of the vertebral lamina and articular processes in screw-tail brachycephalic dog breeds, to evaluate the prevalence of the malformation in a large group of screw-tail dog breeds and to determine if degree of stenosis is associated with presence of neurological signs.

STUDY DESIGN

 This is a retrospective multicentric study.

MATERIALS AND METHODS

 Clinical records of 185 screw-tail brachycephalic dogs (French Bulldogs, English Bulldogs, Boston Terriers) and Pugs were reviewed. Ten dogs with neurological deficits secondary to thoracic vertebral canal stenosis diagnosed on magnetic resonance imaging were identified (Group 1). Neurologically normal dogs (n = 175) of the same breeds underwent computed tomographic imaging of the thoracic vertebral column for other medical reasons (Group 2). Cross-sectional measurements were used to calculate a stenotic ratio.

RESULTS

 Group 1 consisted of three French Bulldogs, six English Bulldogs and one Pug. Eight were males. Most dogs presented with progressive non-painful pelvic limbs ataxia and paresis. Twenty stenotic sites were identified with the most common being T4-T5. Three of ten dogs were treated surgically and all had a good long-term outcome. In Group 2, 33 of 175 dogs had one or more stenotic sites with the most common being T2-T3. The degree of the stenosis was significantly higher in Group 1 (p = 0.019). A stenotic ratio of 0.56 had sensitivity and specificity of 67% to differentiate between dogs with and without neurological signs.

CONCLUSION

 Cranial thoracic vertebral canal stenosis is observed predominantly in young male Bulldogs, but not all stenoses are clinically relevant.

C7 vertebra homeotic transformation in domestic dogs - are Pug dogs breaking mammalian evolutionary constraints?

The number of cervical vertebrae in mammals is almost constant at seven, regardless of their neck length, implying that there is selection against variation in this number. Homebox (Hox) genes are involved in this evolutionary mammalian conservation, and homeotic transformation of cervical into thoracic vertebrae (cervical ribs) is a common phenotypic abnormality when Hox gene expression is altered. This relatively benign phenotypic change can be associated with fatal traits in humans. Mutations in genes upstream of Hox, inbreeding and stressors during organogenesis can also cause cervical ribs. The aim of this study was to describe the prevalence of cervical ribs in a large group of domestic dogs of different breeds, and explore a possible relation with other congenital vertebral malformations (CVMs) in the breed with the highest prevalence of cervical ribs. By phenotyping we hoped to give clues as to the underlying genetic causes. Twenty computed tomography studies from at least two breeds belonging to each of the nine groups recognized by the Federation Cynologique Internationale, including all the brachycephalic 'screw-tailed' breeds that are known to be overrepresented for CVMs, were reviewed. The Pug dog was more affected by cervical ribs than any other breed (46%; P < 0.001), and was selected for further analysis. No association was found between the presence of cervical ribs and vertebral body formation defect, 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 (P = 0.041) and a pre-sacral vertebral count of 26 (P < 0.001). Higher C7/T1 dorsal spinous processes ratios were associated with the presence of cervical ribs (P < 0.001), supporting this is a true homeotic transformation. Relaxation of the stabilizing selection has likely occurred, and the Pug dog appears to be a good naturally occurring model to further investigate the aetiology of cervical ribs, other congenital vertebral anomalies and numerical alterations.

Cervical myelopathy due to complex Atlanto-axial malformation including partial atlantal dorsal arch aplasia in a domestic rabbit

A 1-year-old dwarf rabbit was presented with sub-acute progressive tetraparesis. Radiography, CT and MRI revealed compressive cervical myelopathy secondary to a complex atlanto-axial malformation including partial aplasia of the atlantal dorsal arch, dens malformation, malarticulation and lateral atlanto-occipital displacement. Owners decided against surgical treatment and elected conservative treatment including analgesia with non-steroidal anti-inflammatory drugs, cage rest and physiotherapy. Within 2 months clinical signs deteriorated and the owner elected euthanasia. Subsequent necropsy confirmed imaging findings. Similar cases described in humans and dogs suggest that partial aplasia of the dorsal arch of the atlas might often be an asymptomatic radiologic finding in these species. In contrast, this first description of a similarly affected rabbit demonstrates that complex atlanto-axial malformations can cause severe clinical signs.