Functional Neurosurgery

Dr Vincenzo Levi

Consultant Neurosurgeon, Saint Charles Hospital, Milan, Italy

Dr Levi has been interested in functional neurosurgery since he started his residency at the neurological institute Carlo Besta, where he had the chance to work with many experts in the field. He got inspired by Dr Angelo Franzini, who taught him a lot of things about this subspecialty and how to perform DBS for Parkinson’s Disease, Dystonia and some other rarer neurological conditions, like neuropathic pain and failback surgery syndrome. He is currently starting a program of functional neurosurgery at the same Institute.

Is There a Future for Lesion-Based Approaches in Functional Neurosurgery?

In the ’60s, the main application of functional neurosurgery was lesioning. Before discovering the pharmacological treatment for Parkinson’s disease, functional neurosurgeons treated Parkinson’s with the ablation of some brain nuclei, like the thalamus or the globus pallidus internus. Then the electrical therapy of DBS arrived which is less invasive and damaging than lesioning. So many people thought that the era of lesioning in functional neurosurgery will finish very soon. In recent years, this kind of mentality has changed because there are a lot of reasons to choose lesioning instead of electricity to treat pathological conditions.

What Are the Advantages of Lesion-Based Approaches over Neuromodulation in Functional Neurosurgery?

It’s not always feasible, and especially in developing countries, to have a DBS system, because it’s very expensive and there are many complications, like infections which can be very devastating for the patient. Doing a lesion is totally different, in that you cannot have an infection at all, and you do not have to spend a lot of money on neurostimulators or the electric leads you use in the brain. So in some situations, it’s very advantageous. With the advent of ultrasound, this technique is becoming very popular around the world, because ultrasound is another way to do a lesion in the brain. In the past we had to use a catheter to do a lesion, whereas today we do not need any kind of catheter – we just need a stereotactic apparatus and an MRI to check the lesion by seeing it in the MRI.

Why Is the Subthalamic Nucleus the Most Common Target in Deep Brain Stimulation Surgery?

Historically there were a lot of other targets, like the global pallidus internus and the thalamus, which are part of the same great brain system, the basal ganglia system. It is a system of subcortical nuclei that controls mainly the coordination and the movements of your body. When they are dysfunctional, they can generate some aberrant network that can produce abnormal movements like tremors or dystonia. In the beginning, the globus pallidus internus was the most chosen one, because the first statements were made there. Then in the ’90s, the team of Ben Abid in Grenoble discovered that stimulating the subthalamic nucleus (STN) with high frequency can produce unrest of the tremor. This group then tried to apply these results in Parkinson’s disease and got very good results. So today, the subthalamic nucleus is the most popular and prevalent in terms of targeting around the world.

How Does Targeting in Deep Brain Stimulation Vary between Europe and the US?

I spent almost one year in the US working at UCLA, and the way they stimulate was very surprising for me coming from Europe, because we have this legacy of the Grenoble group and in Europe, we almost still do the same. So I was very surprised to find out that in the US, they do a more personalised DBS. If the major component of the symptomatology is tremor, they do more STN, but for example, if the patient has more levodopa-induced dyskinesia, which are the movements that can be produced after a long therapy with the levodopa, they go for the GPI with great results. And because there is also a controversy about the electrical stimulation of STN – some believe that after a long period of therapy it can produce some problem with cognition, while GPI is not so involved in cognition. So there is this controversy, but I would say that STN absolutely is the most popular one, and it’s a very standard target today. Everyone knows how to target it and which will be the complication of targeting it.

What Are the Surgical Challenges of

Hitting the Subthalamic Nucleus for DBS?

The STN is very small, it’s 8mm3, and the main challenge is to do the right things when planning how to hit the target. I mean you have to be very careful and see with obsession the MRI of your patient, and there are different strategies that you can use. The oldest one is using some reference in your head: the anterior and the posterior commissure, which is called the indirect target. You use a stereotactic atlas and you have to get your coordinate in the brain and you find this point on the MRI. There is also one different technique which I use today, which is hitting the target directly by seeing the MRI. Today, we have very good MRI imaging, 3 Tesla imaging, and from this image, you can see the STN perfectly, and you can target directly on what you see on the MRI. There are some complications, but you can avoid them by seeing the MRI for things like haemorrhages for example. Still, you can plan your trajectory to get to the STN and avoid the small vessel along the tertiary.

Awake or Asleep DBS?

What Are the Pros and Cons of Each Method?

This is a very interesting question because there is an ongoing debate about the possibility to do this kind of surgery asleep as well. I currently do it awake because I’ve been taught like this, and I feel very confident to do this kind of surgery awake, as you have constant feedback from the patient. If there’s something that is not going well, you notice it immediately. But there are some new technologies, like intraoperative MRI or intraoperative CT scan, thanks to which you can immediately check if you’ve hit the target correctly. I guess this kind of technology will change the game, and I can imagine more asleep than awake DBS in the future. If you let the patient choose, I guess they will tell you, “doctor, please, I would like to sleep and not be awake”, because it’s a long surgery that takes up to 6-7 hours, and it’s very stressful for the patient. If you can do this safely with the patient sleeping, I guess this is the best solution.

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