Radiology and Investigations Flashcards
What are the indications for brains imaging
Headache
Raised ICP
Seizures
Weakness or signs of stroke
Trauma
Loss of consciousness
Neurological deficit
Post-operative
What are the advantages of CT for head scans
CT is quick
Can be used in the emergency settings and ICU
Provides great bone detail (good for trauma cases)
Will show up acute bleeds
What are the disadvantages of using CT for head scans
Poor soft tissue detail and contrast
Older bleeds cannot be seen
Radiation exposure
What are the advantages of using MRI for head scans
Best contrast and soft tissue resolution
Shows up marrow and cord pathologies
Can view the cranial nerves
What are the disadvantages of using MRI for head scans
Less bony detail
Not compatible for pacemakers and implants
Takes a lot longer
Not compatible with ICU/emergency equipment
How many sequences do you need for a MRI
Usually need at least 3 sets
Usually T1, T2 and then FLAIR (water suppressed)
Gives a more complete picture
What are the two types of MRI
T1 and T2 weighted
Show up different materials as light and dark
Describe a T1 MRI
Bright sections are fat, methaemoglobin, mineral deposition, melanin and mush (fat and 4M’s)
Contrast will also show up bright if used
Dark areas are water, air and cortical bone, high flow areas (arteries)
Describe a T2 MRI
Bright areas are water, areas with less tissue and fat
Dark areas are blood products, mineral deposition, air and cortical bone, high flow areas
What are the features of ischaemic stroke on a brain scan
Thrombus visible in vessel - will be dense on CT
Areas of ischaemic tissue (blurring of white and grey matter border)
How do haemorrhages appear on brain scans
CT will show up acute bleeds (few hours)
MRI will show up for years
What is the best investigation for brain aneurysm
CT angiogram
Inject contrast
What is the best investigation for skull trauma
CT is the most sensitive
How does a subdural haematoma appear on scans
Concave/crescent shape that follows the brain outline
How does a extradural haematoma appear on scans
Convex/lens shape pushing in towards the brain
The dura is pushed away from the skull by accumulating blood
What is an extra-axial tumour
One found outside of the brain
What is an intra-axial tumour
One found inside the brain
What type of tumour is a pituitary adenoma
Extra-axial - in the pituitary gland not brain
Can be functional and produce hormones
Non-functional and will be silent until they cause mass effect
How does hydrocephalus present on a brain scan
Dilation of the ventricles
What is a Chiari malformation
Congenital brain malformation
Leads to flow obstruction from the 4th ventricle - hydrocephalus (accumulation of CSF)
Leads to mixed upper and lower MN signs
What is cortical dysplasia
Issue that occurs in brain development – cortex is not formed properly
Abnormality seen on scans
What is polymicrogyria
The gyri are small and too numerous
What is Creutzfeldt–Jakob disease
Brain condition caused by prions - can be sporadic, familial or acquired from beef
Patient presents gradually with memory and behavioural changes
Will then progress to coma and death
Water is white on which type of MRI scan
T2
What is an EEG
Electroencephalogram
It is a way of monitoring electrical activity in the brain.
What are EEGs used for
To characterise or help diagnose a range of conditions, particularly epilepsy.
It suuports the diagnosis of epilepsy but is NOT a definitve test
It can help differentiate between seizure type to guide treatment options.
What aspects of an EEG require consent
The first is for hyperventilation and photic stimulation as these have a small chance of evoking a seizure.
The second is for the use of video recording during the test - further consent needed to use these videos for teaching etc.
Why are EEG recorded on video
We see lots of movement and muscle artefact on the recording and use the video recording to confirm what the patient was doing at that time.
If a patient was to have an event during the recording, you have both the video recording and EEG to analyse
How are the electrodes placed in an EEG
An EEG requires 23 electrodes to be accurately attached to the head
Electrodes record from specific lobes of the brain
There is a system of specific measurements taken from landmarks on the head which ensure they are in the correct placed
Skin is rubbed with an exfoliator to lower resistance and then the electrodes are attached using an electrolyte paste
An ECG is recorded at the same time as an EEG - true or false
True
A lead 1 ECG is also recorded – there is an overlay between syncope events and seizures.
How does an EEG work
The electrodes pick up the electrical activity produced by the brain on the scalp. These tiny signals are amplified and sent to the computer to be analysed.
The computer then sorts these electrodes into pre-defined pairs. The waveforms seen are representing the potential difference between two electrodes
What are montages in relation to an EEG
Chains of electrode pairs created by the computer programme
Can be bipolar or reference
In bipolar montages each channel represents the voltage difference between two “poles” on the scalp. These are the standard montages used as they give a wider picture of the electrical activity in the brain
Reference montages compare “point of interest” electrodes to another electrode somewhere else on the body. often used to highlight abnormalities
Which procedures can be used to provoke signs on an EEG
Hypereventilation - Vigorous, deep breathing for 3 minutes results in a transient respiratory alkalosis leading to constriction of the small cerebral blood vessels decreasing O2 supply to the brain
Photic stimualtion - Stimulation with flashes of light to elicit visual responses in the occipital region
Which types of waves are seen on a normal EEG and what affects them
Alpha - most prominent when the eyes are closed and the patient is relaxed
Beta - Augmented by barbiturates and benzodiazepines
Theta - Increases in abundance with drowsiness and light sleep
Delta - Occurs in sleep at all ages but prominent in chidlren
Lamda waves - Can be evoked by looking at colourful patterns and attenuated by looking at blank paper (sharp waves from occipital area)
What are the contraindications for using hyperventilation to provoke an EEG
Aged over 65
Respiratory or cardiovascular disease
Raised intracranial pressure
Cerebrovascular disease
Recent cerebrovascular accident
Moya Moya disease
What can cause an artefact on an EEG
Electrical interference from beds, drips, oximeters and other machinery around the patient.
Movement of eyes, eyebrows, head
Jaw clenching
Rapid blinking
Talking
Yawning and ciughing
A normal EEG excludes epilepsy = true or false
False
Epilepsy is an electro-clinical diagnosis and the clinical background should take precedence over the EEG findings
Nerve conduction studies are used in the diagnosis of which types of disorders
Used for neuromuscular disorders
Includes pathology in the nerve cell bodies or axon, at the NMJ or in the muscle itself
Disorders of the nerve itself is the most common clinical application
Includes anterior horn, roots, plexus and nerves distant to the plexus
List disorders which affect nerves distal to the main plexus
Mononeuropathy - e.g. entrapment
Mononeuritis multiplex - inflammatory process
Polyneuropathy - more diffuse damage, usually length dependant
How are sensory nerve conduction tests carried out
Measure SNAP - Sensory nerve action potential
Apply a stimulus to the sensory area
If stimulus is enough then an AP is generated which is picked up by electrode
This AP can be measured (speed of onset, voltage of response, duration)
Can measure conduction velocity as well
Which types of fibres are tested in sensory nerve action potenital tests
Only large fibre function can be measured
How do post-ganglionic lesions present on SNAP tests
In post ganglionic lesions the SNAP will be abnormal
Seen if there are lesions in pleuxus, nerves distal to plexus or in sensory ganglion
How do pre-ganglionic lesions present on SNAP tests
In pre ganglionic lesions the SNAP will be normal
Seen in radicular pathology and anterior horn cell lesions
How are motot nerve conduction studies carried out
Motor tests are more varied but most basic is the compound muscle action potential
You stimulate the nerve and measure the output at a distal muscle innervated by that nerve (electrodes placed on muscle)
CMAP - sum response of action potentials generated by the various muscle fibres contracting
Measure onset, velocity, amplitude etc
How are motot nerve conduction studies used
Can be used to localise and determine the severity of abnormality
Also specific patterns associated with axonal loss and different types of demyelination (relevant for polyneuropathies as may have genetic and treatment implications)
How would axonal loss present on a motor nerve conduction study
Loss of amplitude
This is because amp represents number of axons
How does demyelination present on motor nerve conduction studies
Slowed conduction or increased latency
What are repetitive nerve stimulation tests used for
This is a specialist test used to investigate myasthenia
How would myasthenia present on repetitive nerve stimulation tests
You stimulate the same nerve multiple times
Will see a reduction in amplitude with repeated stimulus (CMAP decrease >10%)
Usually biggest drop between 4-5th stimulus
What are needle EMG tests used for
To look for evidence of myopathy
Assess the health of the nerve supplying the muscle that is affected/being sampled
How are needle EMG tests carried out
Place needle into the muscle
Assess muscle at rest and then under voluntary movement
Resting muscle should be electrically silent
Muscle activity generates a waveform and associated sound
What are the benefits of needle EMG tests
Needle can assess muscle directly
Can test areas not accessible to standard nerve conduction
Can localise the pathology
How would neuropathy present on a needle EMG test
APs would have long duration, fast firing, high amplitude
How would myopathy present on needle EMG
APs would have short duration, low amplitude, polyphasic
What is the most common use of nerve conduction studies
Diagnosis of carpal tunnel syndrome (median nerve entrapment)
This is also the most common type of nerve entrapment
List some physical barriers to nerve conduction tests
Obesity, oedema, emollients, thickened skin etc
What are the limitation of using nerve conduciton studies to assess ulnar neuropathy
ulnar sensory response can only be measured at risk, distal to actual pathology (usually around the elbow)
