EQUINE VETERINARY EDUCATION / AE / MAY 2019
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Myelography and cerebrospinal fluid analysis A myelogram was performed under general anaesthesia in right lateral recumbency. A spinal needle (20 gauge, 89 mm length) was placed between C1 and C2 and inserted into
the subarachnoid space to collect 60 mL of cerebrospinal fluid with subsequent injection of 60 mL of a nonionic iodinated contrast agent (Iohexol, 350 mg/mL)2. Radiographs were taken in neutral, extended and flexed cervical position. The limited distribution of contrast agent cranially to the injection site and the superimposition with the malformed bones did not allow adequate assessment of the myelographic column in the region between the occiput and the axis, however a subjective narrowing of the dorsal and ventral contrast columns were noted between C1 and C2 suggestive of extradural compression of the spinal cord. The distribution of the contrast agent caudally from the injection site was good, and no abnormalities were detected caudad to C2. Cerebrospinal fluid analysis was performed but did not reveal abnormalities in cell count and cytology.
Fig 1: Right-lateral photograph of the head-neck region. The head is carried in an extended position. Note the prominent wing of C1 (arrow) and the prominent tendon of insertion of the M. longissimus atlantis (star).
Diagnostic imaging
Radiography Lateral and ventrodorsal views of the cervical spine were obtained (Fig 2) using a computed radiography system1. The dorsal arch of C1 in the dorsoventral dimension was moderately shortened. Furthermore, the most dorsal aspect of C1 was positioned considerably more ventral than the spinous process of C2. Both lateral vertebral foramina were not identified on radiographs. The dens of C2 was shortened and blunted. The cranial part of the spinous process of C2 was also shortened and blunted. The ventral part of the atlanto-occipital joint was not fully developed and the joint space was superimposed with mineral opaque material suggestive of partial fusion of the joint.
Computed tomography myelography Computed tomography (CT)3 myelography was performed and revealed an irregular longitudinal split of the entire length of the dorsal arch of C1 (Fig 3). Both wings of C1 had an irregular shape and were smaller than usual. These alterations were more pronounced on the right side. The right cranial articular fovea of C1 was enlarged and sclerotic – associated with a corresponding bony extension of the right occipital condyle. A moderate mineralised bridging of the right part of the atlanto-axial joint was identified. The dens of C2 was shortened and showed a heterogeneous reduced bone density. Between the dens of C2 and the occiput, an irregular linear mineral attenuating structure was detected. This was interpreted as within the apical ligament of the dens, which runs in the vertebral canal between dens of C2 and occiput (Fig 4). At the level of the atlanto-occipital joint, a reduction of about 60% of the myelographic column
Fig 2: Lateral radiograph of the cranial neck. The dorsal arch of C1 is shortened. The dens of C2 (black arrow) and the cranial part of the spinous process of C2 (white arrow) are shortened and blunted.
Fig 3: Transverse computed tomography myelography image (bone window) at the level of the atlanto-axial joint. A longitudinal defect is identified within the dorsal arch (white arrow) of C1 and the surface of the dens of C2 (black arrow) is irregular.
© 2017 EVJ Ltd
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