Brain Imaging Flashcards
What is the first line imagine modality for the brain?
CT
What are the features of CT scans as they relate to the brain?
Well tolerated and fast
Can be with or without IV contrast
Can be used for specialist investigations = angiography
What are some features of MRI scans as they relate to the brain?
Better soft tissue resolution than CT
Longer duration, contra-indicated for some and can be poorly tolerated
What causes ischaemic stroke?
Results for sudden cessation of adequate amounts of blood reaching parts of the brain = divided according to territory affected or mechanism
What does ischaemic stroke lead to?
Deprivation of glucose and oxygen = if circulation not re-established cell death occurs, usually by liquefactive coagulation
What causes ischaemic stroke?
Embolism = cardiac, paradoxical, fat, air, atherosclerotic
Thrombosis = perforator (lacunar infarct), acute plaque rupture with overlying thrombosis
Arterial dissection
What type of MRI is best used for visualising pathology?
T2 weighted scan (T1 best for anatomy)
Why do we image acute ischaemic stroke?
To exclude intracranial haemorrhage and stroke mimics
To confirm ischaemia
To permit rapid treatment
How are ischaemic strokes imaged?
Using non-contrast CT
What is the earliest CT signs of an ischaemic stroke?
Hyperdense segment of vessel = direct visualisation of clot
What are some signs of an ischaemic stroke that can be seen on CT within the first few hours?
Loss of grey/white matter differentiation
Hypoattenuation of deep nuclei
Cortical hypodensity with associated parenchymal swelling with resultant gyral effacement
What causes significant mass effect on CT in ischaemic stroke?
Marked hypoattenuation and swelling
How long does it take for gliosis to be visible on a CT of an ischaemic stroke?
After 24-48hrs = appears as region of low density and volume loss
How does acute blood appear on an unenhanced CT?
Appears white
What are some features of intra-axial haemorrhages?
may be due to acute haematoma = can cause lobar haemorrhage
Can cause midline shift of ventricles
What is an extra-dural haemorrhage?
Collection of blood between inner skull and outer layer of dura = usually associated with skull fracture
What kind of bleed occurs in extra-dural haemorrhages?
Normally arterial = most commonly torn middle meningeal artery
What are some features of extra-dural haemorrhages?
Biconvex in shape = can cause mass effect with herniation
Limited by cranial sutures
What is a subdural haemorrhage?
Collection of blood in subdural space = mainly due to head trauma
What is the first choice imaging technique for subdural haemorrhages?
CT scan
What are some features of subdural haemorrhages?
Semilunar shape and crosses sutures
Has mass effect if large
Subacute appears isodense and chronic appears hypodense
What is a subarachnoid haemorrhage?
Blood in the subarachnoid space = hypodense material seen in space
Where do subarachnoid haemorrhages commonly occur?
Around the circle of Willis
What are some causes of subarachnoid haemorrhages?
85% associated with berry aneurysms
May be related to trauma or other vascular malformations
What are some features of subarachnoid haemorrhages?
Can have larger volume of high attenuation acute blood in sulci, sylvian fissures and supracellar cistern
What is CT angiography used for in subarachnoid haemorrhages?
To look for berry aneurysms
What are some complications of a subarachnoid haemorrhage?
Hydrocephalus, vasospasm, infarction
What kind of group of tumour are intracranial tumours?
Heterogenous group of tumours
What are the majority of intracranial tumours in adults?
Metastases = from lung, breast, renal cell or colorectal cancer, or melanoma
What is the first line investigation for intracranial masses?
CT = hypo/hyperdense, often rounded
CT useful for determining oedema or mass effect
Why may contrast be used when imaging intracranial masses?
May make lesions more conspicuous
What are some features of metastases?
Usually multiple = supra/infratentorial
Lots of oedema and mass effect
Avidly enhance
What does the grade of a primary tumour influence?
The degree of oedema, mass effect and enhancement seen
