Medical imaging: Neuroimaging Flashcards
- MrsJones is a 86 year old lady who was admitted to your surgical ward following a fall at home and head injury. She is awaiting emergency surgical repair of a neck of femur fracture.
- The nurse calls you to tell you MrsJones is ‘not quite herself’ and is not responding to her name.
•Question: What action should you take?
what reasons can you think of for her drowsiness?
- Go see the patient and assess using the A to E approach
- Potential reasons for drowsiness:
- Infection (URTI/LRTI/UTI) always rule out sepsis
- Hypoxia, hypercapnia
- Metabolic reasons? Always check glucose
- Medication? morphine etc
- Cardiovascular –> MI/ PE
- Neurological? –> Stroke
what is the A to E approach?
Airway Breathing Circulation Disability Exposure/ Everything else
- Airway –> look for any signs of airway obstruction, paradoxical chest and abdominal movements, use of accessory muscles, central cyanosis. Complete airway obstruction = no breath sounds at mouth or nose, partial obstruction air entry is diminished an noisy. Depressed conciousness can lead to airway obstruction
- Breathing –> look for any signs of resp distress (as above plus sweating), count RR, assess depth of breath and pattern,chest expansion, chest deformity, pulse oximeter, breath sounds, percuss and auscultate chest, check position of trachea
- Circulation –> perfusion of hands, limb temp, cap refill time, veins (underfilled or collapsed = hypovolaemia), pulse peripheral and central, BP, ausculate heart, reduced conciousness, haemorrhage (external or internal suspected, e.g. surgical pt.), take blood from cannula, give fluids and reasses, listen for crackles (do not want to fluid overload). Any signs chest pain ECG.
- Disability –> check drug chart, examine pupils, GCS, blood glucose
- Exposure –> examine pt properly, full exposure may be needed but maintain dignity.
What is the GCS scale?
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- On assessment MrsJones is very drowsy, but has no focal neurological deficit. On discussion with your registrar, a plan to image MrsJones head is made.
- Which imaging modality would be best suited and why?
- What would you like the radiologist to confirm or refute?
Need to work out whether pt is suffering ischaemic or haemorrhagic stroke. CT or MRI of the head is the first test to do.
Imaging modality best suited = CT, fast.
CT angiography (CTA) may be performed. In CTA, a contrast material may be injected intravenously and images are obtained of the cerebral blood vessels.
Images that detect blood flow, called CT perfusion (CTP), may be obtained at the same time
Querying ischaemic or haemorrhagic stroke –> is there any intracranial bleeding?
When should you perform immediate (within 1 hr) brain imaging for pts with suspected acute stroke?
Perform brain imaging immediately with non enhanced CT for pts with any of following:
- Indication for thrombolysis or thrombectomy
- anticoagulant treatment
- known bleeding tendency
- depressed GCS (below 13)
- unexplained progressive or fluctuating sx
- papilloedema, neck stiffness, fever
- severe headache at onset of stroke sx
- If thrombectomy indicated, perform contract CT angiography
- perform scanning as soon as poss within 24 hrs of sx onset in everyone w suspected acute stroke without indication for immediate brain imaging
Describe the systematic approach for going through a CT head?
- Check demographics –> Name pt, DOB, date and time of scan, any previous imaging
- Viewing scan as if looking at the patient from the feet up
- compare both sides for symmetry
Pneumonic –> Blood Can Be very Bad
- Blood –> Extra axial bleeding
- Can –> Cisterns –> CSF forms cisterns (pools) within the subarachnoid space
- Be –> brain –> loss of sulci, loss of grey/ white matter differentiation, midline shift, foci of hyper/ hypo dense tumours
- Very –> Ventricles –> enlargement, effacement (compression), blood filled (note choroid plexus if frequently calcified)
- Bad –> Bone window, look for fractures or soft tissue injury
Describe the image shown:
Top R image
bottom R image
What does the green line indicate?
what strctures are shown?
Top R window –> sagital section
Bottom R windown –> coronal section
Green line indicates the level at which the axial plane is.
Part of the frontal lobe, the central sulcus and the parietal lobe can be seen plus part of the superior sagittal sinus.
Label the image
Label the image
How does the view of structures change at a lower axial level?
- Start to see more of the frontal sinus dominating at the front
- Revealed more basal ganglia structures, the head of the caudate nuclues and thalamus
- The anterior and posterior horns of the lateral ventricles
- The tempral lobe and occipital lobe are visible at the back.
- The third ventricle inbetween the thalami
- Superior sagittal sinus meeting the inferior sagittal sinus
Label the image
Label the image
Describe the circle of willis
Two vertebral arteries unite to form the basilar artery which gives off the potine arteries supplying the pons of the brainstem.
Before the vertebral arteries unite to form basilar artery they give off the posterior inferior cerebellar artery on either side and the anterior spinal artery medially.
Before the pontine arteries come off the basilar, the anterior inferior cerebellar artery comes off. After pontine arteries the superior cerebellar artery comes off either side.
Next is the posterior cerebral artery –> posterior communicating which communicates with the ICA which directly gives off middle cerebral artery.
Anteriorly we have the anterior cerebral arteries which are connected by the anterior communicating artery.
Describe the vascular territories of the cortex
The ACA supplies the medial part of the frontal and the parietal lobe and the anterior portion of the corpus callosum, basal ganglia and internal capsule.
MCA: The cortical branches of the MCA supply the lateral surface of the hemisphere, except for the medial part of the frontal and the parietal lobe (anterior cerebral artery), and the inferior part of the temporal lobe (posterior cerebral artery).
PCA: Cortical branches of the PCA supply the inferomedial part of the temporal lobe, occipital pole, visual cortex, and splenium of the corpus callosum.
Describe the blood supply to the cortex and subcortical structures
- PICA supplies occipital surface of cerebellum and is in equilbrium with the AICA which supplies it more laterally.
- Superior cerebellar artery (SCA) is in the superior and tentorial surface of the cerebellum
- Branches from vertebral (medulla) and basilar artery (pons) supply brainstem
- Anterior choroidal artery supplies hippocampus, posterior limb internal capsule.
- Lenticulostriate arteries –> lateral arise off MCA, supplies most of basal ganglia, medial arise off ACA, supplies head of caudate and anteroinferior internal capsule.
- ACA –> most of medial part of frontal and parietal lobe, anterior portion corpus callosum, basal G and internal capsule
- MCA –> lateral surface of hemispheres (except medial frontal and parietal and inferior temporal lobe).
- PCA –> supplies inferomedial temporal lobe, occipital pole and visual cortex, splenium of corpus callosum.
- Thalamogeniculate arteries off PCA supply blood to midbrain and thalamus.
Which arteries supply the pons and cerebellar territories shown?
Which arteries supply the medulla?
Describe the evolution of CT head signs
At first haemorrhagic stroke is easy to see:
Bleeding shows white / attenuating
It then becomes darker as it becomes more watery
Ischaemia (hard to see initially), may have some loss of grey-white matter differentiation or swelling, as time goes on –> low desnity with negative mass effect
Why is a non contrast CT used to rule out bleeding in stroke diagnosis?
What are hounsefield units?
HU= hounsefield units, measure of how much tissue is attenuating (how opaque structure is on CT, e.g. bone high attenuation, highly opaque, high density).
As bleeding starts it is hyperattenuating, then in the subacute window it starts to match with grey and white matter, and then overtime appraoches 0 HU.
Which image has contrast in it?
The right hand image has contrast within it, the choroid plexus is lit up in both images (note these are not areas of blood collection.)
What is digital subtraction angiography?
- Digital subtraction angiography (DSA) = technique used in interventional radiology for visualising blood vessels
- Image taken without contrast, then image of the vessels taken with contrast, then radioopaque structures are “subtracted” digitally from the image –> thus allowing for accurate depiction of the blood vessels
What are the features of extradural haemorrhage?
- Extradural haematoma = blood collection between the skull and endosteal layer of the dura mater.
- Typically seen in young patients who sustain head trauma, usually with an associated skull fracture.
- Commonly lentiform in shape, bound by skull sutures
- Often associated with mass effect compression on the brain, increase in ICP and can cause herniation.
- Source of bleeding often arterial, often middle meningeal artery
What is a subdural haemorrhage (where is the blood?)
Who does it tend to affect?
What is its classical shape?
How does it appear on CT?
- SDH –> Blood collecting within the potential space between the meningeal layer of the dura and the arachnoid mater.
- Clasically venous, seen in all ages but more likely in the elderly when the cerebral bridging veins have become stretched (or in dehydrated or alcoholic patients.)
- Appearance is crescent shaped
- Homogenously hyperdense (as it is blood)
- It can follow sulci, the internal margin parallels the cortical margin of the adjacent brain and can cross sutures.
- More extensive that EDH
What type of bleed is this?
Crescent shaped, homogenously hyperdense extra axial collection that spreads diffusely over affected hemisphere.
Acute SDH with hyperdense region on CT.
sometimes acute SDH can be isodense to adjacent cerebral cortex; occurs with anticoagulation, coagulopathies or severe anaemia.
What type of bleed is this
This is a subacute subdural haematoma over the left hemisphere
As clot ages and protein degradation occurs density starts to drop, density will eventually become isodense to adjacent cortex
What pathology is shown?
Subarachnoid haemorrhage
What are the uses of MRI?
what are the different weightings and their uses?
MRI:
- Slower, more expensive but high resolution imaging
- Acute stroke –> oedema
- Degeneration and demyelination
- Tumours
- Neuroinfection
- Hydrocephalus
- Spinal cord
T1 weighting –> fluid appears dark, provides most anatomically relevant images, grey matter is darker than the white matter
T2 –> standard sequence, fluid id bright, white matter is darker than grey
DWI –> Diffusion weighted imaging, shows how easily water moves around, resticted diffusion will occur in stroke due to necrotic tissue, useful to highlight ischaemia
