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.