Page 92 - Canine Lameness

64 4 The Neurologic Examination

have both orthopedic and neurologic disease. Some patients presenting early in a neurologic
disease process, such as a nerve sheath tumor, may only display lameness as a sole deficit, mak-
ing differentiation from orthopedic disease very difficult. Typically, orthopedic causes are easiest
to exclude first with an orthopedic examination, and if any identified abnormalities are nonex-
planatory or no abnormalities are found, neurodiagnostics (e.g. neuroimaging) are then
pursued.
General considerations regarding diagnostic imaging technologies are discussed in Chapter 10.
Multiple abnormalities may be found on neuroimaging, and the clinician will need to determine
their clinical significance. Any abnormality needs to be interpreted in light of the clinical history
and corroborated with the neurologic examination.

4.4.1 Survey Radiographs

Orthogonal spinal radiographs can be used to assess vertebral structures, intervertebral disc spaces,
and intervertebral foramina. To accomplish ideal positioning, sedation is generally advised.
Mineralized intervertebral discs may be evident in the foramen or canal and occasionally neoplas-
tic lesions can cause enlargement of the intervertebral foramen from pressure atrophy. Bone lysis
due to discospondylitis or neoplasia may also be seen, depending on chronicity.

4.4.2 Myelography
Myelography is an imaging examination where contrast material is injected into the subarachnoid
space followed by either radiographs or computed tomography (CT). The images, called myelo-
gram, can provide information on the spinal canal, spinal cord, meninges, subarachnoid space,
and nerve roots. It is helpful in detecting extramedullary compressive lesions, but it is frequently
not useful in identifying intramedullary, foraminal, nerve root, or nerve lesions.

4.4.3 Computed Tomography
CT has the advantage of being a fast imaging modality but does have limitations regarding its ability
to diagnose neurologic lesions. Similar to myelography, CT is useful in detecting compressive
extramedullary lesions, such as mineralized intervertebral discs. However, compared to magnetic
resonance imaging (MRI), CT images provide limited information on the nerves and intramedullary
diseases, such as neoplasia and fibrocartilaginous emboli (FCE). If a herniated intervertebral disc is
not mineralized, it will not be easily detectable on CT. CT can be combined with myelography and/
or an intravenous contrast agent to increase the diagnostic accuracy.

4.4.4 Magnetic Resonance Imaging
MRI is the imaging modality of choice for the CNS and PNS. MRI is valuable in identifying inflam-
mation or regions of edema, which signify pathology. Structural lesions (such as intervertebral disc
herniation), soft tissue proliferation secondary to discospondylitis or spondylomyelopathy, neopla-
sia, and intramedullary pathology (e.g. FCE) are also detectable by MRI. Intravenous contrast can
be administered and may accentuate some lesions, especially those outside of, or disruptive to, the
blood–brain barrier, e.g. certain neoplasms, meningitis, and discospondylitis.