Surgery in Movement Disorders Flashcards
Traditional Neurosurgery restores abnormal anatomy
- Aims to modify pathological anatomy
- Usually deals with acute disease
- Often lifesaving surgery
Why should we perform functional neurosurgery?
- Surgical intervention - change in function
- patient with chronic neurological disorders
- Rarely life threatening
What is the ultimate aim for functional neurosurgery?
To improve symptoms and quality of life
What are the indications for functional neurosurgery?
- symptoms of movement disorders: PD, dystonia, tremor
- Chronic pain syndromes: phantom pain, cluster headache
- Neuropsychiatric conditions: Tourette, OCD, depression
- Epilepsy
What does functional neurosurgery demand?
Minimal risk of inflicting morbidity and mortality
In 1930, what did the american neurosurgeon suggest?
Basal Ganglia were involved in the control of movement
What is the history of surgery for movement disorders: desperate measures?
Lesions can modulate the brain circuits that control the movement
- Victor Horsley-1890
- Corticospinal tract
- Stereotaxis - Meyers 1930
- Basal Ganglia
- Open procedures
What is the stereotactic technique?
- Accurate navigation within the brain in a minmally invasive fashion
- Horsely and Clarke frame (1905)
- Hindered by lack of imaging - Spiegel & Wycis (1947)
- Ventriculography
- Internal landmarkers
- Need for stereotactic atlases
What did Irving Cooper do?
- He made a small temporal craniotomy – lifted the brain up and he went underneath the brain to cut the cerebropeduncle – he was cutting the corticospinal tract rather than taking all of the cortex out disconnecting the cortex by dividing the corticospinal tract
- He nicked the anterior choroidal artery on his way in – he couldn’t stop the bleeding
- Place a small silver clip across the small blood vessel to occlude it
- Anterior choroidal artery goes to the basal ganglia
- Ligation of the left anterior choroidal artery
What can lesions positively alter?
Neural function
History: lesions can positively alter neural function
- Surgery for Parkinson’s disease, chronic pain, psychiatric disorders
- Tens of thousands of pallidotomy/thalamotomy procedure was performed - there was no other treatment
What happens if you ligate the anterior choroidal artery in 40 patients?
About 2-3 patients will die because the anterior choroidal artery has variability it is very big
Why did surgery fall out of favour?
- The age of drugs
- L-dopa 1967 (Cotzias)
- Chlorpromazine - Indiscriminate use of lobotomy by psychiatrists
Why has surgical neuromodulation made a come back?
- Intolerable side effects
- Lack of efficacy
- Motor fluctuations
Parallel circuits … with significant crosstalk!
- This shows you some of the major connections between different areas of the brain – doesn’t show you all of the connections
- The model is clear that the cortex sends information via the corpus stratium through the Basal Ganglia and back to the cortex via the thalamus
- There are circuits that are running in parallel between motor parts of the cortex, limbic part of the cortex and cognitive/associative part of the cortex – these go through the basal ganglia in parallel but there is a lot of crosstalk between them
- There is a lot off cross talk between these circuits
Parkinson’s disease
you lose a lot of neurons in particular neurons of the substantia Nigra in pars compacta
• Parkinson’s disease has various stages – start losing nigral neurons quite late – start losing gut cells and medullary cells far before we start losing substantia nigra cells – you have to lose 50-70% of your nigra cells before you get symptoms
What is substantia nigra pars compacta?
Susceptible pathophysiology of alpha-synuclein accumulating in parkinsonian nerve cells - they have a very high metabolic requirement
What does alpha-synuclein affect?
Mitochondrial functions
What do each substantia nigra pars compacta cells thought to make?
100,000 synapses with different neurons throughout the brain
What happens when you lose substantia nigra?
You get a mismatch and cardinal symptoms of Parkinson’s diseaseget mismatch of activity in various parts of the basal ganglia
What happens when the thalamus doesn’t excite the cortex?
The cortex gives the bradykinesia
When do we get an improvement?
• If we put a lesion in the subthalamic nucleus in the Globus pallidus interna or stick an electrode and pass an electrical current through the area blocking the information that is going through that pathway
What is the function of the parallel circuits?
- Function of the brain is information processing
- Brainstem is the vegetative part of the brain – breathing and cardiac function, acid-base balance, homeostasis
- Reactive system – saw tooth
- Subconsciously you are making a prediction of what is going to happen – if the prediction is wrong, the movement will be pathological
- Emotion is an internal prediction of what is happening on outside
What will help with movement?
If we lesion STN
What can different circuits control?
Different symptoms of different movement
What can treat different symptoms?
Different targets of the brain
Where is subthalamic nucleus situated between?
Midbrain and diencephalon - target that and improve all cardinal symptoms in Parkinson’s disease - improve motor fluctuations
What do symptoms dictate?
Brain target: tailored surgery
Subthalamic nucleus (STN)
- Can help with dopamine responsive symptoms
- Improves motor fluctuations, braykinesia/akinesia, rigidity, gait, tremor
- Reduction in medication
- psychological side effects - Speech articulation
Pallidum
- Effective for dyskinesia/dystonia
- Less likely to interfere with psychology
- Does not improve bradykinesia much
Motor thalamus (Vim)/Zona incerta (ZI)
Useful in tremor
What are the advantages and disadvantage of lesion?
- Advantages:
- Cheap
- No implanted hardware - Disadvantage:
- Irreversible
What are the advantages and disadvantages of high frequency stimulation
- Advantages:
- socially more acceptable
- Relative reversible - Disadvantages
- Expensive
- Labour intensive
- Hardware problems
Deep Brain Stimulation: Mechanism of action:
- It has an effect on voltage gated channels by blocking action potentials
- It activates inhibitory axons and most neurons in your brain are inhibitory
- You can deplete transmitters at synapses
- Disrupting network activity
DBS: mechanism of actions?
- High frequency stimulation has a similar clinical effect to lesioning
- Effect increases with rate and reaches a plateau
What are the physiological effect of DBS?
- Effect on V-gated channels block action potentials (depolarisation blockade
- DBS activates inhibitory axons (synaptic inhibition)
- Transmitter depletion (synaptic depression)
- Disruption of network activity (desynchronisation)
What are the many initial concern for MRI in functional neurosurgery?
- Geometric distortion
- Targeting accuracy
- Efficacy
Methods of compensating for geometric distortion
What does MRI raise the possibility of?
Acquiring the target on the first pass through the brain in the majority of cases
- important safety implications
What is the reference point
mid-commissural point– that is between the anterior commissure and the posterior commissure – you can see these points in ventriculograms, also seen on CT and MRI
The subthalamic nucleus
roughly 12mm from the midline and 2mm behind the mid-commissural plane, 5mm below the AC-PC line
What is found lateral to the lentiform nucleus?
the putamen, medially there is Globus pallidus – divided into both externa and interna and there is a lamina between them
If your motor is post-lateral
your limbic is inferior-medial (temporal lobe) and you associative is in the front – those circuits are the same
What does recognising the firing of patterns of neurons tell us?
that we are in the subthalamic nucleus
What is the brain?
Very vascular organ– it receives 20% of your blood flow
Adjust target to visualised image
- Direct Targeting
- Corrects for anatomical variation
- Requires the recognition of the imaging correlates of anatomical structures
- Multiple imaging planes (redundancy)
Thalamic Targets
- Thalamic nuclei not reliably visualised at 1.5T
- More reliance on atlas based coordinates
- more forigiving target
- stronger role for LA - Anatomical clues from pallidothalamic border/ relationship to ZI
