S12) Imaging of the Head & Neck Tissues

Question 1

What are the different imaging modalities used in head and neck imaging?

Answer 1

• X-Rays
• USS
• CT
• MRI
• Angiography
• Functional Imaging (Isotopes, PET)

Question 2

How does one choose between different imaging modalities?

Answer 2

The choice of imaging modality depends on the type of tissue and/or pathology that is being investigated

Question 3

Which is the most commonly requested imaging investigation in clinical practice?

Answer 3

Plain radiography e.g. chest x-rays, hand x-rays, facial x- rays

Question 4

What are the advantages and disadvantages of plain radiography?

Answer 4

• Advantages: cheap, readily available, relatively low radiation, helpful for visualising bony structures
• Disadvantages: not helpful for viewing tissue other than bone

Question 5

In injury or pathology involving the head and neck region, more detailed imaging is often required such as CT scanning.

What are the advantages and disadvantages of this imaging modality?

Answer 5

• Advantage: 3D cross-sectional views, detailed views of bone, soft tissue and brain
• Disadvantage: higher radiation dose than radiographs

Question 6

In some instances MRI may be the imaging of first choice depending on what type of pathology you are trying to find or investigate.

What are the advantages and disadvantages of this imaging modality?

Answer 6

• Advantages: detailed 3D, cross-sectional views, greater soft- tissue detail than CT
• Disadvantages: more expensive, much noisier, takes longer (up to 30 minutes) than CT, many contraindications

Question 7

There are a number of contraindications to MRI, mostly due to the use of strong magnetic fields.

Identify some of these

Answer 7

Presence of metallic foreign bodies e.g. stents, pacemakers, joint replacements, cochlear implants

Question 8

In some instances MRI may be the imaging of first choice depending on what type of pathology you are trying to find or investigate.

Describe the uses of MRI

Answer 8

• Not used as a first-line investigation in acute and/or immediately life threatening conditions
• Used to further investigate pathology that has been identified by CT scanning to gain greater clarity of detail
• Useful for looking at muscle and determining margins between normal and abnormal tissue

Question 9

Rank the density of tissues on a CT scan from least to most dense

Answer 9

Air < Fat < Fluid < Soft tissue & blood < Bone < Metal

Question 10

Indicate how the appearance of structures varies in a CT scan according to their relative density

Answer 10

Air < Fat < Fluid < Soft tissue & blood < Bone < Metal

Black → darker to lighter shades of grey → bright white

Question 11

Explain how the appearance of structures varies in plain radiography according to their relative density

Answer 11

• Bone – high-density structure, appears as bright white
• Air – low density structure, appears as black

Question 12

In terms of visualising structures with varying densities, explain why CT scanning is the preferred imaging modality to the plain radiograph

Answer 12

• CT scans can better differentiate between subtle density differences e.g. between fluids, soft tissue and air as well as between different fluid types
• This allows for varying shades of colour i.e. white, black and scales of grey

Question 13

A “window” can also be set while viewing the CT images so that certain tissues of interest can appear with greater clarity and become more readily seen.

Identify and describe some of these different windows

Answer 13

• Soft tissue window – to view most organs
• Lung window – to view lung parenchyma on a CT chest
• Bone window – to view bones in clearer detail on a CT head/neck

Question 14

How does one distinguish between an epidural and subdural haemorrhage on an MRI scan?

Answer 14

• Extradural haemorrhage = lemon appearance
• Subdural haemorrhage = banana appearance