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EQUINE VETERINARY EDUCATION / AE / MAY 2019
resonance imaging examination was performed using a 3T magnet (Philips Ingenia 3T)4. The pathological findings of the occiput, C1 and C2 identified with CT were confirmed. The altered apical ligament of the dens was easily recognisable. Spinal cord compression at the level of the dens of C2 was also identified. There was no evidence of any fibrosis or gliosis of the nervous tissue that would indicate chronic tissue damage.
Necropsy findings and anatomic preparation
Fig 4: Sagittal plane multiplanar reformat computed tomography myelographic image. Note the irregular hypoattenuating defects within the dorsal arch of C1 (black arrows), the irregular shape of the dens of C2 (grey arrow), the shortened spinous process of C2 (black star) and the mineral attenuating focus in the region of the apical ligament of the dens of C2 (white arrow).
Both rectus capitis ventralis and lateralis muscles were missing bilaterally. Instead of them, a thin and long muscle extending from the cranial aspect of the transverse process of C2 to the muscular tubercle of the occipital bone was identified. This abnormal muscle was only visible after dissection and retraction of the longus capitis muscle (Fig 6). Furthermore, the cranial oblique muscle of the head had an abnormal firm consistency on palpation. The atlas showed the most severe abnormalities. The
cross-sectional shape of this bone was rectangular instead of squarish. As previously observed by CT and magnetic resonance imaging, a longitudinal split with a width of 4– 9 mm was present along the entire dorsal arch of C1 (Fig 7). Both wings of C1 were smaller and thicker than normal, and both had an incisura alaris instead of a foramen alare (Fig 7). The cross-sectional area of the spinal canal was substantially smaller at the level of C1 than at the level of the occiput and C2. Finally, the ventral tubercle of C1 was small.
Fig 5: Sagittal plane multiplanar reformat computed tomography myelographic image of C1 and C2. Note that the ventral contrast
column at the level of C2 is obliterated while the neck is in flexion (white arrow) and a mild narrowing of the dorsoventral dimension of the spinal cord is identified. A dorsal displacement of C2 due to hypoplasia and malformation of the dens (white star) is clearly visible.
dorsolaterally on the right side was detected. However, the cross-sectional area of the spinal cord was comparable in size to the adjacent cord. The ventral contrast column at the level of C2 disappeared while the neck was in flexion and a slight compression of the spinal cord was detectable at this location (Fig 5). In flexed position, the dens of C2 was clearly identified displaced dorsally due to hypoplasia and malformation (Fig 5). The mare underwent euthanasia after the CT examination was completed due to the poor prognosis.
Post-mortem magnetic resonance imaging Post-mortem, the mare’s neck was sectioned between the 7th cervical and the 1st thoracic vertebra and a magnetic
© 2017 EVJ Ltd M. longus colli
M. longus capitis
Fig 6: Ventral view of the neck musculature. Both rectus capitis ventralis and lateralis muscles are missing bilaterally. Note the bilateral thin and long muscle (stars) extending from the cranial aspect of the transverse process of C2 to the muscular tubercle of the occiput. This abnormal muscle was only visible after dissection and retraction of the longus capitis muscle.
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