Imaging the Spinal Cord Flashcards
When is plain XR used in skeletal imaging of the spine?
What views are typically used?
- plain XRs are used to image the cervical, thoracic and lumbar spine
- CT C-spine has superseded the use of plain XRs in trauma
- these XRs are commonly requested in A&E following trauma
- the AP and lateral are the standard views of the thoracic and lumbar spine
- there are some indications for plain XRs of the spine without a history of trauma - usually for progressive / worsening back pain
When is imaging of the C-spine requested?
How is the C-spine positioned following trauma?
- imaging of the C-spine is indicated in certain circumstances after trauma, such as:
- falling from a height
- head injury
- RTA
- attempted hanging
- direct blow
- the C-spine is immobilised after major head trauma (or other generalised trauma), if patient has low GCS or “distracting” injuries
- neck pain after a minor RTA (whiplash) or neck pain without trauma can make it difficult to know when to image the C-spine
What is used to assess cervical spine injury?
- patients with suspected spinal injury are assessed for cervical spine injury using the Canadian C-spine rules
- these are used to assess whether a patient is at high, low or no risk of a C-spine injury
According to the Canadian C-spine rules, when is someone deemed to be at high risk of C-spine injury?
- age 65 years or older
- paraesthesia in the upper or lower limbs
- dangerous mechanism of injury, such as:
- fall from height > 1m or 5 steps
- axial load to the head - high-speed motor accident, horse riding accidents, rollover motor accident, ejection from a motor vehicle
According to the Canadian C-spine rules, when is a person deemed at low risk from a C-spine injury?
if they have one of the low risk factors and are unable to actively rotate their neck 45 degrees to the left and right
the range of the neck can only be assessed safely if the person is at low risk and there are no high-risk factors
- involved in a minor rear-end motor vehicle collision
- comfortable in a sitting position
- ambulatory at any time since the injury
- no midline cervical spine tenderness
- delayed onset of neck pain
According to the Canadian C-spine rules, when is someone deemed to have no risk of C-spine injury?
- if they have one of the low-risk factors and are able to actively rotate their neck 45 degrees to the left and right
What 3 steps should be performed if someone is at high risk of C-spine injury?
- carry out / maintain full C-spine immobilisation
- request imaging - CT in adults
- proceed to MRI if after CT there is neurological abnormality that could be attributed to spinal cord injury
What is the first line imaging modality in suspected C-spine injury?
- some patients will have CT C-spine, some will have XRs and some will need no imaging at all
- CT is increasingly being used as first line
- if XRs are used then 3 views are needed - if there are any abnormalities / suspicions then CT is performed
How many vertebrae are present within the C-spine?
What are the standard views used to image this and why?
- there are 7 vertebrae within the C-spine, some with a unique morphology
- the 3 standard views are the AP, lateral** and **PEG (“open-mouth”)
- all 7 vertebrae plus T1 need to be seen
- a “swimmer’s view” may be required to visualise C7 and T1
What is unique about C1 and C2?
C1:
- this is known as the atlas and it articulates with the base of the skull
C2:
- this has a modified vertebral body that forms the odontoid peg (dens)
- the dens is responsible for the rotation of the head
What is involved in the systematic approach to interpreting C-spine XRs?
- look for fractures, abnormal alignment and soft tissue signs
What are each of the following lines that need to be interpreted on C-spine lateral XR?
- anterior vertebral line
- posterior vertebral line
- spinolaminar line
- posterior spinal line
What is normal prevertebral soft tissue thickness?
- < 7mm above C5
- < width of one vertebral body below C5
“7 at 2 and 2 at 7”
What are the following features?
What should be assessed on an image like this?
- look for alignment, fractures (tracing cortices) and symmetry of the joint spaces
What is meant by a “swimmer’s view”?
Why is this view used?
- the arm adjacent to the vertical grid is elevated and flexed and the forearm is rested on the head for support
- the other arm is depressed and moved slightly anterior to place the humeral head anterior to the vertebrae
- the central ray is centred to T1 and directed perpendicular to the shoulder
- the idea is to move the humeral heads anteriorly so that they do not obscure the C7-T1 junction
What is an alternative way to perform the swimmer’s view?
- the patient is placed prone on the table with the left hand abducted 180o and the right hand to the side (as if swimming)
- the cassette is placed against the right side of the neck
When might imaging of the thoracolumbar spine be performed?
- to rule out fracture following trauma
- if there is clinical suspicion of bony pathology in patients with atraumatic back pain
What are the following features of the AP L-spine?
What are the following features of the lateral L-spine?
What can be assessed in this view?
- the normal curvatures of the spine can be assessed
- the lumbar spine is lordotic
When is an oblique L-spine view performed?
How can this be interpreted?
- to visualise the articular facets and pars interarticularis of the lumbar spine
- it is associated with the typical “scotty dog” appearance
What are the features of the “scotty dog” on oblique lumbar spine view?
- ear = superior articular process
- eye = pedicle
- neck = parts interarticularis
- legs = inferior articular processes
- tail = contralateral superior articular process
- nose = transverse process
What is meant by the “owl eye” appearance of the lumbosacral spine?
What does it mean if the owl eye becomes white and what condition is this frequently associated with?
- the spinous processes form the beak of the owl
- the pedicles form the eyes of the owl
- the pedicles should line up and not be sclerotic
- prostate cancer is associated with sclerotic bone metastases - these present as a “white owl’s eye” on lumbosacral spine XR
What is the winking owl sign?
- this occurs when a pedicle is absent
- this is almost always due to bony metastasis
In an oblique L-spine view, what does it mean when the scotty dog is wearing a collar?
- the neck of the scotty dog is the pars interarticularis
- a chronic fracture in this region results in the margins becoming sclerotic/white
- this gives the appearance of a dog wearing a collar
What is shown in these AP and lateral thoracolumbar spine images?
What is the major risk associated with this fracture?
crush fracture / wedge fracture
AP view:
- the vertebra has been crushed down and widened
- the owls eyes have become separated as the vertebra has lost height
- the upper and lower margins of this vertebra cannot be seen
Lateral view:
- there is retropulsion as bony fragments have been displaced backwards and into the spinal canal
- bone retropulsion presents a risk of spinal cord compression / cauda equina syndrome
What signs might be seen on an XR of degenerative disc disease (DDD)?
- the discs become progressively reduced in height as they degenerate
- the margins become sclerotic
- lipping osteophytes form at the margins of the disc (around the lips)
- sometimes the osteophytes connect together to form syndesmophytes
- ankylosing spondylitis is associated with many syndesmophytes along both sides of the cord, producing a “bamboo spine”
What is a burst fracture?
What is the associated risk?
- the vertebral body bursts as a result of trauma
- the spinal canal is at risk from the many fragments of bone produced in this form of trauma
How does discitis present on scan?
- there is infection of the disc, which causes erosion of the bone
- the pathology is within the disc and erodes the bone of the adjacent end plates
- this produces a diffuse, permeative loss of the margis of the end plates
What is shown in this image?
What condition is it often mistaken for?
vertebral metastasis
- it appears as though the tumour is “eating” chunks out of the bone
- haemangioma is a benign vascular lesion within the vertebral body that produces a honeycomb appearance
When is a T1 scan beneficial?
How do fat and water appear on this scan and why?
T1 scans provide excellent anatomical detail
- the T1 signal is a measure of how quickly nuclei relax
- hydrogen nuclei in fatty tissues relax quickly, meaning they appear bright and are “high signal”
- hydrogen nuclei in tissues with a high water content relax more slowly, so these appear dark and are “low signal”
When is a T2 MRI image beneficial?
How does fat and water appear on these images and why?
good for pathological detail
- T2 signal is a representation of nuclei desynchronising
- hydrogen nuclei in fatty tissues desynchronise rapidly and “lose” signal more quickly, meaning they appear darker
- hydrogen nuclei in tissues with a high water content desynchronise more slowly and have a high T2 signal and appear bright
- fat appears bright on T1 and T2 images, so the fluid signal is used to differentiate between the 2
