Neuroimaging

Question 1

What are the aims of imaging in neurological cases?

Answer 1

• Narrow down, confirm, rule-out differential diagnoses
• Surgical planning
• Staging
• Prognosis
• Co-morbidities
• Extra-neurological causes
• Treatment response

Question 2

When does imaging come in as a part of the investigation of neurological disease?

Answer 2

1. Clinical examination
2. Neurological examination
3. Neurolocalisation & problem list
4. Initial list of differential diagnoses
5. THEN Diagnostic test, including imaging - imaging cannot replace any of the previous steps

Question 3

List 3 neurological conditions that would have expected imaging changes allowing you to confirm a diagnosis

Answer 3

• Paraparesis
• Change in mentation (neoplasia)
• Post traumatic signs (fractures)

Question 4

Describe the use of radiography for neurological cases

Answer 4

• Associated with bone lesions (fractures, luxation, discospondylitis, tumours?, otitis media)
• Rule out of bone-associated lesions
• Limited value for intracranial conditions
• Limited value for spinal “soft tissue” conditions unless myelography

Question 5

When is aural radiography indicated?

Answer 5

Chronic otitis
Peripheral vestibular syndrome
Facial nerve paralysis
Horner’s syndrome
-> Middle ear disease

Question 6

What is better than radiography for aural imaging?

Answer 6

CT

Question 7

Which radiographic projections are useful for aural imaging?

Answer 7

• Lateral (but superimposition of bullae)
• Open mouth rostrocaudal (might be difficult in brachycephalic dogs)
• Allows identification of L or R bullae
• Oblique views

Question 8

Describe the use of radiography for spinal imaging and how to get the best image

Answer 8

• Lateral and ventrodorsal (spine closer to the plate) radiographs to identify location correctly
• Importance of straight positioning (use pads under neck and lumbar region)
• Exposure in expiratory pause (to prevent motion artefacts)
• In multiple sections to avoid geometric distortion
• Centre on region of interest

Question 9

Describe ‘horses heads’ seen on radiography

Answer 9

Intervertebral foramina (lumbar) = window into the vertebral canal

Question 10

Which dog breed is most commonly known for their mineralised intervertebral discs?

Answer 10

Dachshund

Question 11

What are the 5 radiographic signs?

Answer 11

1. Shape (Think about symmetry)
2. Margination (Are the cortical margins intact?)
3. Opacity (Radiolucent or sclerotic?)
4. Location (Alignment with adjacent vertebrae – luxation)
5. Number (Monostotic, polyostotic = one bone or multiple bones)

Question 12

Describe the main features of Atlanto-axial subluxation

Answer 12

• Congenital malformation of the dens or excessive laxity of the ligaments
• Toy breeds
• Less common after trauma

Question 13

Describe the normal angulation and abnormal angulation seen in Atlanto-axial subluxation

Answer 13

• Marked angulation between atlas and axis is abnormal
• The dorsal margin of the vertebral canal of the axis and atlas should form a continuous straight line
• The angle becomes much more acute in subluxation

Question 14

Describe fractures of the vertebrae

Answer 14

• Traumatic versus pathological
• Traumatic fracture often also subluxated
• Pathological fracture often compression fractures - additionally lysis or periosteal reaction

Question 15

What is discospondylitis?

Answer 15

Infection of an intervertebral disc and osteomyelitis of adjacent endplates
- Changes to the disc not visible
- Changes to the endplates after ~3 weeks
- Often lumbosacral junction

Question 16

What are the 4 main features of discospondylitis?

Answer 16

• Irregular endplates: lysis
• Periosteal reaction (new bone)
• Sclerosis next to lysis
• Soft tissue swelling ventrally

Question 17

Myelography allows you to assess?

Answer 17

For soft tissue lesions within the vertebral canal
Determine location, shape, size

Question 18

Soft tissue lesions in the vertical canal can be in which 3 locations?

Answer 18

Extradural
Intradural – extramedullary
Intramedullary

Question 19

How is myelography performed?

Answer 19

• Injection of iodinated positive contrast medium into subarachnoid space
• Followed by orthogonal radiographs
• Outlines surface of spinal cord
• Not a Day 1 competence
• Potentially severe complications!
• Interpretation can be challenging

Question 20

When is CT indicated as an imaging modality?

Answer 20

Suspected bone lesion
- Trauma
- Abnormal anatomy
Otitis media
Large intracranial tumours?
Peripheral nerve tumours?
Concurrent disease

Question 21

When is MRI indicated as an imaging modality?

Answer 21

• Most things BUT not bone
• Brain and spinal cord parenchymal lesions
• Seizures
• Intervertebral disc extrusions
• Muscular lesion

Question 22

List the main features of MRI

Answer 22

• No ionising radiation
• VERY strong magnetic fields!
• Safety is great concern
• Strict rules for access and what can enter the room
• Fatal accidents possible
• MRI physics are complex
• Excellent soft tissue resolution
• Different “sequences” and contrast medium (gadolinium) can highlight differences between tissues
• Radiological signs still used for lesion characterisation (“signal intensity” instead of “opacity”)

Question 23

Compare degenerative disease and discospondylitis

Answer 23

• Degenerative intervertebral disc disease is common
• Usually asymptomatic
• But can precede disc herniation or predispose for infections
• If severe differentiation can be difficult (use other modalities)
• Degenerative disc disease has smooth end plates unlike discospondylitis

Question 24

What is Spondylosis deformans

Answer 24

Typical bridging or spur-like new bone arising from the ventral aspect of the endplates
Not clinically significant (until proven otherwise)
Very rare