CNS Imaging

Question 1

What are plain films useful for in terms of the CNS?

Answer 1

Only occasionally used to look at the skull (but mostly CT now)
Previously used for pneumoencephalography

Question 2

What is catheter angiography?

Answer 2

A flexible catheter is inserted through the aorta and travels through the vessels of the neck and head, where contrast is injected in order to visualise the cerebral vessels

Question 3

When is ultrasound a relevant technique for CNS imaging?

Answer 3

In neonates (can image through fontanelles)

Question 4

What is Doppler ultrasound used for when imaging the CNS?

Answer 4

Used in adults to measure flow in the MCAs

Question 5

What is the appearance of grey and white matter in a T1-weighted MRI?

Answer 5

Grey matter appears grey

White matter appears white

Question 6

What is Blood Oxygen Level Dependent (BOLD) imaging and when is it used clinically?

Answer 6

Imaging which measures local regulation of blood supply over a small area (a specific action is performed and the area responsible for regulating that action increases its oxygen delivery by vasodilating local vessels)
Used when resecting a tumour and attempting to avoid/predict effects of resection

Question 7

What types of nuclear medicines are available for brain imaging and when are these used?

Answer 7

Single positron emission computer tomography (SPECT) and positron emission tomography (PET)
Used to assess the metabolic function of the brain with labelled glucose e.g. in epilepsy (to determine site of seizure), AD (hypometabolism in areas of neurodegeneration before macroscopic changes appear)

Question 8

What is the basis of tractography and when is it used?

Answer 8

Movement of water is limited by axons
Brain can be divided into voxels and the dominant direction of the movement of water can be mapped to determine the trajectory of fibres
Used to image the white matter tracts e.g. to determine where to enter for tumour resection (avoid disrupting tracts)

Question 9

What is the drawback of using CT to image the cortex?

Answer 9

Grey and white matter have similar densities on CT and require a narrow window to be able to distinguish them; this produces a relatively “noisy” image

Question 10

What are T1 weighted images useful for?

Answer 10

Provide the best differentiation between grey and white matter
Able to identify areas of cortical thickening as seen in migrational disorders e.g. grey matter heterotopia, focal cortical dysplasia

Question 11

What are T2 weighted images useful for?

Answer 11

Outlining areas of abnormal physiology
“Water sensitive” and can detect areas of abnormal water content due to abnormal metabolism of normal cells (e.g. inflammation leading to oedema) or abnormal cells (e.g. tumours, cortical dysplasia)

Question 12

What 2 structures make up the lentiform nucleus?

Answer 12

Caudate nucleus and globus pallidus

Question 13

What are the basal ganglia?

Answer 13

Deep grey matter structures of the brain

Includes caudate nucleus, globus pallidus and putamen (+/- thalamus, subthalamic nuclei, substantia nigra, claustrum)

Question 14

What is the clinical relevance of the basal ganglia in terms of their metabolic requirements?

Answer 14

More metabolically active and therefore more susceptible to injury (i.e. anoxia occurs here first)

Question 15

List 4 imaging methods/modalities that can be used to image intracranial arteries

Answer 15

Digital subtraction angiography (DSA)
CT angiography (CTA)
MR angiography (MRA)
Transcranial ultrasound

Question 16

What are watershed strokes and what usually causes them?

Answer 16

Strokes occuring in the area between vascular territories

Typically due to hypoperfusion, often superimposed on a stenosis

Question 17

List 3 imaging methods/modalities that can be used to image intracranial veins and dural sinuses

Answer 17

Digital subtraction angiography (DSA)
CT venography (CTV)
MR venography (MRV)

Question 18

Where does the superior anastomotic vein of Trolard run between?

Answer 18

Middle cerebral vein and inferior sagittal sinus

Question 19

Where does the inferior anastomotic vein of Labbe run between?

Answer 19

Middle cerebral vein and transverse sinus

Question 20

How is inferior petrosal sinus sampling performed and why?

Answer 20

Catheters enter either side of the pituitary gland to supply a corticotrophin analogue; the inferior petrosal sinus (where the pituitary drains) is then sampled for ACTH and this is compared to serum levels
Used in suspected pituitary microadenoma

Question 21

What is FLAIR MRI imaging and what is it used for?

Answer 21

Fluid-attenuated inversion recovery (nulls CSF)

Used to assess for periventricular hyperintense lesions (e.g. MS plaques)