Atlantoaxial malformation in a half-Arabian colt.
Abstract: A 1-year-old half-Arabian colt was referred for evaluation of a cranial cervical abnormality. Physical examination revealed the left wing of the atlas to be more ventral than the right wing. A head tilt, with the pole deviated to the left, was present because of the malpositioned atlas. Neurologic examination identified symmetrical weakness, ataxia, and proprioceptive deficits in all four limbs. Radiographs of the cranial cervical region revealed fusion of the atlas and axis, and deviation of the atlantoaxial joint to the left of the median plane. Euthanasia was elected. Necropsy confirmed the radiographic findings. The atlas was rotated 20 degrees counterclockwise when viewed from the caudal aspect. Multifocal myelomalacia was present in the first and second cervical spinal cord segments. The malformation was believed to be due to a degenerative process or abnormal embryological development.
Publication Date: 1991-01-11 PubMed ID: 1993394
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Summary
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This study looked at a case of atlantoaxial malformation in a 1-year-old half-Arabian colt that was causing it to have severe physical and neurological symptoms. It was determined that the colt’s abnormal condition may have been caused by either a degenerative process or issues during its embryological development.
Investigation and Examination
The half-Arabian colt, aged just one year, was brought in due to an observed cranial cervical abnormality. Here is a rundown of the examination process:
- The physical examination showed that the left side of the colt’s first vertebra in the neck (the atlas) was lower than the right, leading to a tilt of the head with a deviation towards the left.
- A neurological examination identified symptoms of symmetrical weakness, unsteady movement (ataxia), and deficits in sense of position and movement of the body (proprioceptive deficits) in all four limbs.
Radiographic Findings
Further medical investigations were conducted to verify the nature of the orthopedic condition, notably:
- Radiographs of the cranial cervical region, the top part of the neck, indicated fusion of the first two vertebrae in the neck, the atlas and axis, and deviation of the joint between these (the atlantoaxial joint) to the left of the midline.
Outcome and Necropsy Findings
Due to the severity of symptoms and prognosis, euthanasia was decided on for the animal. A necropsy or post-mortem examination led to the following findings:
- As seen in the radiographs, it was confirmed that the colt’s atlas was indeed rotated about 20 degrees counterclockwise.
- Areas of softening or necrosis within the spinal cord (myelomalacia) were noted in the first two cervical spinal cord segments. This suggests that the malformation caused severe damage to the colt’s spinal cord leading to its symptoms.
Possible Causes of Malformation
The examination and necropsy results suggested that the abnormal union and deviation in the top two neck bones, along with the asymmetrical positioning of the atlas, were due to either:
- A degenerative process where the colt’s vertebrae had degraded over time, or
- Abnormalities during the embryological development of the animal, causing the malformation to occur before its birth.
Cite This Article
APA
Blikslager AT, Wilson DA, Constantinescu GM, Miller MA, Corwin LA.
(1991).
Atlantoaxial malformation in a half-Arabian colt.
Cornell Vet, 81(1), 67-75.
Publication
Researcher Affiliations
- Department of Veterinary Medicine and Surgery, College of Veterinary Medicine, University of Missouri, Columbia 65211.
MeSH Terms
- Animals
- Atlanto-Axial Joint / abnormalities
- Atlanto-Axial Joint / diagnostic imaging
- Axis, Cervical Vertebra / abnormalities
- Cervical Atlas / abnormalities
- Horses / abnormalities
- Male
- Radiography
Citations
This article has been cited 4 times.- Cole R, Taintor J, Hanson R. Atlanto-axial malformation in an adult Quarter horse gelding. Can Vet J 2017 Sep;58(9):923-925.
- Bordbari MH, Penedo MCT, Aleman M, Valberg SJ, Mickelson J, Finno CJ. Deletion of 2.7 kb near HOXD3 in an Arabian horse with occipitoatlantoaxial malformation. Anim Genet 2017 Jun;48(3):287-294.
- Hülsmeyer VI, Flatz K, Putschbach K, Bechter MR, Weiler S, Fischer A, Feist M. Traumatic odontoid process synchondrosis fracture with atlantoaxial instability in a calf: clinical presentation and imaging findings. Ir Vet J 2015;68(1):6.
- Aleman M, Dimock AN, Wisner ER, Prutton JW, Madigan JE. Atlanto-axial approach for cervical myelography in a Thoroughbred horse with complete fusion of the atlanto-occipital bones. Can Vet J 2014 Nov;55(11):1069-73.
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