History
An 11-year-old warmblood gelding weighing 540 kg presented as a tertiary referral to a UK referral hospital with an 8 month history of ataxia and neck pain.
Eight months previously, the patient was considered clinically well with no neurological abnormalities and subsequently underwent general anaesthesia for surgical resection of a melanoma from the sheath with assisted recovery. During recovery the patient ventroflexed the neck and impacted the head. Following recovery, the patient was markedly ataxic in all limbs. Reported clinical examination findings immediately post recovery found no localising swelling or pain. Analgesia and anti-inflammatories (phenylbutazone, morphine and dexamethasone) as well as Vitamin E were administered post-operatively.
The patient’s condition reportedly improved over the following days’, however a mild degree of ataxia remained. Radiographic examination of the neck did not detect any significant abnormalities. The ataxia improved with conservative management and physiotherapy.
Re-examinations found an improvement of clinical signs in the following 3 months but the owner reported the neck felt intermittently hot and uncomfortable. Medication of the C4-C5, C5-C6 and C6-C7 articular process joints was performed during this time.
Upon presentation to the Liphook Equine Hospital, 8 months following onset of clinical signs, findings from clinical and neurologic examination included; bilateral muscle loss surrounding the caudal cervical spine as well as loss of left gluteal musculature. There was no pain on palpation throughout the neck or the epaxial musculature. A marked restriction of neck motion was found in every direction, particularly in the dorso-ventral plane. Cranial nerve examination was normal. Dynamic neurological examination found bilateral weakness during tail pull tests with a severe weakness when pulled to the right side. When walking in a straight line, tight circling, up and down a slope and on serpentines, the patient was hypermetric, particularly in the hind limbs, with circumduction during circling. This was consistent with grade 4 hind limb ataxia and grade 1 fore limb ataxia . Given the clinical presentation a lesion within C1-C7 was most likely leading to the ataxia and therefore a CT was considered the most appropriate diagnostic modality.
CT examination of the head and entire cervical spine was performed under general anaesthesia. Both plain and positive contrast myelographic CT studies were acquired. A 16 slice multidetector CT (GE Lightspeed Modified CT) with a helical acquisition at 120kV, 300mA and 1.25mm slice thickness, field of view 60cm, reformatted using both a bone and soft tissue algorithms to 0.625mm and 3mm slice thicknesses, matrix size of 768 x 768.
Positive contrast myelogram was performed via atlantooccipital cisternal puncture with an 8.3cm needle. A short extension tube was attached and 10ml cerebrospinal fluid per 100kg bodyweight was removed over a 3 minute period. The same volume of iohexol (Omnipaque 300mg I/ml GE Healthcare) was then injected over a 3 minute period. Once needle withdrawal had occured, the head was elevated for 3 minutes to allow caudad flow of contrast material. The head and neck were then lowered and repeat CT imaging was performed.
Recovery from anaesthesia was unassisted and graded as excellent. Post-operatively the patient was given 4.4mg/kg phenylubutazone intravenously as a single dose.
Results from cytological examination of the cerebrospinal fluid were within normal limits (mildly xanthochromic, Protein 10 g/l)- Table1.
CT findings revealed a complete, chronic, moderately displaced articular fracture of the left ventral tubercle of the atlas. A saucer fracture of the caudodorsal articular margin of the left occipital condyle with an associated intraarticular osseous fragment. The atlantooccipital joint was moderately effused. Soft tissue proliferation was present within the left half of the vertebral canal, extending from the occiput to the caudal aspect of the atlas, narrowing the vertebral canal by approximately 50% and causing right dorsal displacement of the spinal cord. This was causing marked extra-dural compression of the contrast column at the left side in the myelographic images. Gas attenuating material was present within this soft tissue material in post myelographic images, likely iatrogenic and secondary to injection Figures 1-5).
Moderate osteoarthropathy of the atlantooccipital joint was present, most markedly left sided. Enthesous new bone was present at the insertion of the joint capsule and associated ligaments at the caudal aspect of the occiput.