Acute neurologic events are challenging, since the type and severity of the trauma can determine whether the animal will recover function or have permanent deficits. The spinal cord is encased in the vertebral column, and the complex structure and deep position limit the utility of first line imaging tools.
CT excels at detecting details of bone such as fractures or luxations, and is capable of detecting spinal canal abnormalities as well. In contrast, MRI’s strength is imaging the spinal cord and soft tissues. Used together, these modalities can detect all the pieces of the puzzle of a spinal injury. From fracture, to luxation, traumatic disk herniation, and hemorrhage, we can determine the extent of the injury and help the clinician and owner with treatment and prognosis.
This excerpt from the Atlas of Small Animal CT and MRI is from Section 3.2, Traumatic and Vascular Disorders. We hope you enjoy it!
Thoracolumbar fracture/luxation
Between 49% and 58% of vertebral fracture/luxations involve the T3–L3 region in dogs and cats, and 24–38% involve the L4–L7 region. Most fractures in this region are associated with clinically significant neurologic deficits. Motor vehicle trauma has been reported as the most common cause for thoracolumbar fracture/luxation in dogs, whereas cats are just as likely to sustain injuries from a fall. Although there are some differences between cats and dogs, vertebral luxation or fracture/luxation has been reported to be the most common injury for both, followed by wedge compression fractures, transverse fractures, and subluxation and hyperextension injuries. Multiple compartments are involved in the majority of injuries; endplate involvement is seen in approximately a third, and rotational displacement and intervertebral space involvement is present in more than half. Fracture/ luxation also occurs with greater frequency at junctions between mobile and less mobile regions of the vertebral column.
Traumatic intervertebral disk extrusion
Intervertebral disk extrusion can occur as the direct result of trauma and can be either compressive or noncompressive. Both normal disks and those with nuclear degeneration are at risk, but degenerate disks more often lead to spinal cord compression. Normal nucleus pulposis is composed predominantly of water, and when herniated through the annulus, fibrosis can dissipate into the epidural fat or through the dura mater and into the spinal cord. This can result in an intrinsic spinal cord lesion with no overt evidence of compression. Because degenerate nucleus pulposis contains more solid mass, traumatic extrusion is more likely to result in spinal cord compression. CT features of traumatic intervertebral disk extrusion include disk space narrowing with or without extradural spinal cord compression. The latter feature is best seen using CT myelography. The MR features of traumatic intervertebral disk extrusion in dogs include reduced volume and T2 signal intensity of the affected disk and increased spinal cord T2 intensity at the level of disk extrusion. Extrusion of degenerate disk material is more likely to result in an extradural compressive mass.
Spinal cord trauma
Contusion/hemorrhage
Spinal cord trauma is usually but not always accompanied by overt vertebral column trauma. Neurologic deficits range from clinically silent to complete spinal cord transection. In addition to the primary spinal cord injury that results directly from trauma, secondary injury occurs from vascular damage, local cytotoxic biochemical responses to injury, and inflammatory response, the combination of which can lead to progressive disease. Postmortem examination of spinal cords of dogs and cats that sustained traumatic injury revealed thoracolumbar necrosis that correlated with the degree of static compression from vertebral column injury. Cervical cord injury often included central hemorrhagic necrosis that was more consistent with transient impact trauma than static cord compression.
MR features of spinal cord contusion include focal to regional increased T2 intensity with mild to no enhancement following contrast administration. T2* sequences reveal parenchymal susceptibility effects when there is a hemorrhagic component. Syringohydromyelia is often a late sequela to spinal cord trauma and appears as a focal to regional and central to eccentric T2 hyperintensity.
Homework
Consider whether your patients would benefit from one or both modalities, and use the case examples in the book to compare the imaging findings. The Atlas of CT and MRI is available through Amazon, and has over 700 figures showing case examples to further your learning. Check it out if this article was helpful!
See you next time,
Allison Zwingenberger
Co-Author, Atlas of Small Animal CT and MRI
P.S.
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