Occipital Dysplasia Associated To Atlantooccipital Subluxation In Dog. Case Report

Lorigados CAB, Guiffrida LA, Reis HMG.

Occipital Dysplasia Associated to Atlantooccipital Subluxation in Dog. Case Report. International Veterinary Radiology Association, 2009.


The occipital dysplasia is characterized as a foramen magnum malformation, which presents an abnormal dorsal extension, due to incomplete ossification of the ventromedial supraoccipital bone. It is frequently described in small breed dogs, though there are reports in medium breed dogs, like Beagle and Cocker Spaniel. It can also be associated to others abnormalities, with the atlas dorsal arch shortening, odontoid agenesis or hipoplasy and affections that involves the central nervous system, as syringohydromyelia, cerebral herniation or hydrocephalus. The atlantooccipital subluxation has been mentioned in literature as traumatic, either for occipital condyles or atlas fractures, resulting in an articular instability. In men, atlantooccipital joint subluxation is characterized in Down’s syndrome patients, resulted by ligaments lassitude in this region of the patients. It wasn’t found reports of the association between occipital dysplasia and atlantooccipital subluxation in dogs.


This report describes a three months old female Poodle breed dog presenting cervical hyperestesia, tetraparesy, thoracic and pelvic limbs proprioceptive loss of 1 month’ duration, with progressive worsening. There was no traumatic historic. A radiograph in rostrodorsal- caudoventral view of the skull presented a foramen magnum malformation and according to the foramen dorsal extension measure compared to its total height was classified as a second degree occipital dysplasia (moderated). In lateral view of the cervical spine was observed an atlas ventral dislocation compared to occipital condyles (subluxation). There were no C1 vertebral body and occipital condyles fractures. It was prescribed oral prednisone and cervical collar. The animal came to death within two days after the consultation and the owner did not allow the necropsy.


Lots of dogs that present occipital dysplasia are asymptomatic, what suggests that the foramen magnum morphological alteration alone is not the cause of neurologic dysfunctions. Atlantooccipital articular instability can cause spinal cord compression and respiratory arrest due to rostral segment of medulla and bulb infarction, by vertebral artery compression and occlusion, what might explain the patient’s death. Although there is no trauma historic and the simple radiograph couldn’t evidenciate any bone fracture involving an atlantooccipital joint, many authors claim the need to a computed tomography to detect traumatic alterations of this region that is not possible to be detected in conventional radiographic examination. The magnetic resonance examination can also evaluate ligament structures and other central nervous system alterations that can be associated.