EQUINE VETERINARY EDUCATION / AE / MAY 2019


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Fig 7: Dorsal view of C1. Note the longitudinal split in the dorsal arch of C1 (white arrow) and the presence of an incisura alare (black arrows) instead of a foramen alare and the bony proliferations/rough bony surface on the dorsal arch of C1 (black star).


Fig 9: Cranial view of C2. Note the irregular shortened shape and surface of the dens containing several cavities (black arrows) and the irregularity of the spinous process of C2 (black star).


Fig 8: Caudal view of the occiput. Note the asymmetry of the foramen magnum (white arrows) and the bony proliferations on the right occipital condyle (black star).


The nuchal crest of the caudal part of the occiput was


asymmetric. The foramen magnum had an asymmetric ovally shaped form. The right occipital condyle was covered by bony proliferations (Fig 8). Bony proliferations were also present at the right cranial fovea articularis of C1 indicating partial atlanto-occipitial ankylosis. The dens of C2 was abnormally short and had an irregular


surface and contained several cavities (Fig 9). The axis showed a slight curvature to the right, whereas the C3 was distinctly curved to the left. The C4 showed a curvature in the same direction as C2. This curvilinear shape of C1 to C4 resulted in a scoliosis of the cranial cervical spine.


Histology Small samples of spinal cord and synovialis of the atlanto-axial joint were collected and sections (2–3 lm) were mounted on glass slides and stained with haematoxylin–eosin using standard procedures. Histological examination of the spinal cord revealed swelling of the myelin sheaths with few


Fig 10: Transverse histological section of the M. obliquus capitis


cranialis stained with Masson–Goldner. Note the generalised fibrosis, which can be recognised by blue stained collagenous bundles (black arrows) between sparse muscle fibres.


myelinophages located within the sheaths. Rarely, the axons were completely missing (mild Wallerian axonal degeneration) mainly affecting the ventral funiculus. The grey matter was without pathological findings. The cranial oblique muscle of the head was sclerotic, i.e. exhibited thick


collagenous bundles and fatty tissue between sparse muscle fibres (Fig 10). Additionally, the synovialis showed papilliforme proliferations with hyperplastic and hypertrophic epithelium. The connective tissue was slightly infiltrated by lymphocytes and plasma cells. Thus, a mild chronic proliferative inflammation of the atlanto-axial joint was present.


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