Acute CT Brain Flashcards
How to differentiate between a fracture or a suture on a brain CT
- Sutures* are found in anatomical locations and characteristically jagged with corticated edges.
- Fractures* are generally straight and not corticated, will often have an accompanied intracranial haemorrhage
What’s the issue with identifying basal skull fractures and how do we get around this?
They can be difficult to identify, but in the setting of a head injury, a fluid level (blood) in the sphenoid sinus can be a helpful sign
How does brain volume change with age?
Brain volume decrease throughout adulthood/dementia/alcoholism.
Eg; small ventricles in a child and large ones in adults are both normal
What is Hydrocephalus and how is it seen on CT
the result of increased production or decreased absorption of CSF.
This can result in a massive enlargement of the ventricles.
What happens with acute hydrocephalus
May cause damage to the ependyma (the lining of the ventricles) which results in oedema of the periventricular white matter.
“transependymal oedema”
Characteristic features of Alzheimers disease on brain CT
- Reduced volume of temporal lobes
- ****medial side especially***
- Enlargement of the temporal horns of the lateral ventricles
- specific sign of volume loss of the temporal lobes
What can happen with increased brain volume/cerebral oedema
- Brain swells → generalised reduction of the CSF space volume and loss of differentiation between grey/white matter.
Generalised low density of the cerebral white matter is a common sign of?
Chronic ischaemia due to small vessel disease
many patients with chronic small vessel disease also have generalised loss of brain volume.
What do old lacunar infarcts look like on brain CT and what vascular territory are they in?
Appear as small areas of well-demarcated areas of low density on CT due to cell death.
This is the same for all old territorial infarcts
In the typical distribution of the MCA perforator branch territory.
* acute infarct may not be clearly visible!
What do you see on an initial CT in the setting of acute ischaemic stroke?
Often nothing! the main purpose of this is to exclude intracranial haemorrhage.
- Subtle low density in the affected area
- “hyperdense artery”
- “insular ribbon sign”
- these are all often overlooked!
What is this sign and what does in indicate?
This is the ‘Hyperdense artery sign’ and occurs in the setting of an acute infarct, where thromboembolic material may be within a cerebral artery
(most commonly MCA)
What is this sign and what does it indicate?
the insular ribbon sign
The insular normally has a thin layer of cortexr, but in the context of acute infarct, this can be lost.
Intracranial bleeding is either intracranial (inside brain), or extra-axial (outside brain)
what are the three types of extra-axial haemorrhage and what do they look like??
- Extra dural haematoma: lens shaped collection
- Subdural haematoma: Cresent shaped collection
- Subarachnoid haemorrhage: occupy CSF spaces; sulci, fissures, ventricles, basal cisterns
When do you get extradural haemorrhage, what artery is usually damaged and how does this cause the haemorrhage?
A post-traumatic event resulting from an injury to an intracranial artery (usually MCA).
Leakage from affected artery → collection of blood which strips the dura mater away from the inner table of the skull (so lens shaped collection is tightly held by the dura to the limitation of cranial sutures)
When do you get subdural haematoma what vessel is usually damaged and how does this cause the haemorrhage?
Eldery and anticoagulated patients have more fragile cerebral veins.
Minor trauma or even no trauma can cause injury to these.
Not limited by dural attachment points to bone → cresent shaped instead.
**no blood extends into the sulci as the arachnoid remains intact
Common and less common causes of subarachnoid haemorrhage?
Commonly: trauma or spontaneous bleeding from intracranial anaerysm.
Only visible on CT if large
Uncommonly: spontaneous congenital arteriovenous malformation or perimesencephalic subarachnoid haemorrhage (bleeding from veins around brainstem)
What is the mechanism for the distribution pattern of subarachnoid haemorrages?
Small foramina connect the subarachnoid space with the fourth ventricle.
Blood can therefore pass into any part of the CSF space: sulci, fissures, ventricles, basal cisterns
Intra-axial haemorrhage, or ‘intracerebral haemorrhage’, can be due to ________
spontaneous or trauma reasons
These can look IDENTICAL.
look for fractures.
Both are often accompanied by leakage into the extra-axial spaces.
What are the usual suspects form Intra-axial lesions seen on brain CT.
Intra-axial lesions are more commonly neoplastic and malignant over benign.
- Single intra-axial lesions with ‘ring-enhancment’ post-contrast:* likely primary malignant mass (Glioma)
- Multiple lesions:* likely metastatic
What is this and what will happen post-contrast?
Likely intra-axial brain metastises that will show ‘ring-enhancement’ post-contrast
Most common extra-axial lesion and its characteristics?
meningioma: benign but can grow very fast with a larger adjacent area of adjacent cerebral oedema.
- Smooth edge
- Rounded shape
- Central Calcification
- dural tail
- Bright enhancement of whole lesion post-contrast
What is “mass effect”?
The brain is a soft tissue structure inside a cranial vault.
It’s volume cannot change, so any ‘space-occupying lesion’ may increase IC pressure and displace the brain tissue.
Many pathological processes can do this, and surrounding cerebral oedema often worsens this (why infarcts can actually be ‘space occupying’)
What are the stages of mass effect on the brain
- Effacement of the sulci adjacent to the lesion
- Partial/complete effacement of the adjacent ventricles
- for both this may extend across the whole hemisphere
- Displacement of the midline structures
- Effacement of contralateral sulci and ventricles
***5. Extreme cases may show herniation of structures through the incisura tentorii (gap at top of ten normally occupied by the brainstem & basal cisterms) or coning (extrusion of the posterior fossa structures through the foramen magnum) = poor prognosis
