Epilepsy Surgery Unveiled: Resection, Disconnection, and Cutting-Edge Neurostimulation

In this edition, I aim to explore Epilepsy Surgery in more depth, covering the different types of surgical interventions available, including resection, disconnective surgeries, and neurostimulation device implantation. We'll delve into how these procedures work, who might benefit from them, and the potential outcomes for patients.

Why Epilepsy Surgery?

It is important to establish that in 30% of patients, Anti-Epileptic Drugs (AEDs) are ineffective in stopping or reducing epileptic seizures. This condition is known as as Drug Resistant Epilepsy (DRE) or Refractory Epilepsy. Hence for those patients with DRE, alternative treatment approaches must be taken to help manage their seizures.

Hence, epilepsy surgery in this case would become a point of consideration, as a final resort, due to the risks that it holds, such as complications, infection, emergence of alternative side effects - all of which will be discussed throughout.

Epilepsy Surgery can help to reduce the epileptic seizures, or in some cases, eliminate them completely. For example, according to the Epilepsy Society , approximately 70% of individuals who undergo temporal lobe surgery become seizure free, with 50% of patients maintaining this seizure-free status even after 10 years. However, we must note that each epileptic case is unique of it's own, and so has it's own personalised treatment approach.

Epilepsy Surgery Eligibility

These are the following conditions to be eligible for epilepsy surgery:

1. Tried two or more AEDs - all of which have been unsuccessful in controlling or reducing the seizures
2. Have a type of epilepsy that can be treated using surgery - usually focal epilepsy

Tests must be completed to find the seizure origin in the brain, and whether this part of the brain could cause any complications or side effects in the patient.

Resective Surgery

This is the most common type of epilepsy surgery, and involves the surgical removal or 'resection' of the part of the brain causing the seizures (seizure origin) to prevent further seizure production.

This type of surgery is only compatible with those who have focal epilepsy, as the seizure origin is confined in a specific area that can be surgically removed.

There are 3 main types of Resective surgery including:

1) Temporal Lobe resection

This is the most common type of surgery for those with Temporal Lobe focal epilepsy which involves the removal of the part of the temporal lobe contributing to the occurrence of the seizures. This procedure can also be referred to as Temporal Lobectomy.

Due to the role of the temporal lobe in memory, one of the risks of this surgical operating is the decline in memory.

This surgical operation can also be performed in the other lobes of the brain (frontal, occipital and parietal) - and can be referred to as 'Extratemporal surgery'. Their risks are associated with disrupting their respective functions which can be found here.

2) Lesionectomy

This surgical procedure involves the removal of lesions, tumours or abscess (swollen parts with accumulated puss) in the brain which are causing the seizures. This is also for focal epilepsy.

Risks associated with a Lesionectomy are associated with the location of the lesion, due to the risk of damaging any surrounding brain structures, which could impair any particular functions within the individual, such as memory or vision.

Another risk involves the type of lesion, as there may be a risk of regrowth of the lesion post-surgery. This would require close monitoring with doctors after the surgery.

3) Hemispherectomy

This is an extremely rare procedure, where it's purpose is to functionally isolate or eradicate the epileptogenic zone. This procedure is only conducted on patients with focal epilepsy, where their seizures originate on only one brain hemisphere.

This procedure can be split into 2 types:

1. Anatomic: surgical removal of an entire affected hemisphere (including the frontal, occipital, parietal and temporal lobes) that is causing the seizures
2. Functional: This is both a resective and disconnective surgery (see below), that involves:

• Removing a smaller portion of the diseased hemisphere (rather than completely removing it)
• Disconnecting diseased hemisphere from the healthy, normal hemisphere.

The corpus callosum (a bundle of nerve fibres connecting the two hemispheres) is cut, to stop seizures from spreading to the other healthy brain hemisphere.

The risks of this procedure depend on the site of surgery and type of surgery performed, however potential risks involve major problems in bleeding, infection, loss in motor skills, muscle weakness, visual impairment, allergic reaction to anaesthesia and speech difficulties.

More information on Hemispherectomy can be found here.

Disconnective Surgery

Disconnective epilepsy surgery aims to reduce seizures by cutting or 'disconnecting' the nerve pathways of which the seizure impulses travel through the brain.

This procedure is usually done for drug resistant patients with severe, uncontrolled seizures, who either have generalised epilepsy, or have focal epilepsy where the seizures originate in a section of brain tissue that cannot be safely removed.

Aside from Functional Hemispherectomy which has been discussed earlier, there are 2 other types of Disconnective surgeries which are: Corpus callosotomy and Multiple subpial transections.

Corpus callosotomy

This procedure is utilised for those with severe, drug resistant generalised epilepsy. It involves the cutting of the Corpus callosum, to prevent seizure impulses from travelling from one hemisphere to another.

Corpus callosotomy can be performed as a 'partial callosotomy', where only two-thirds of the Corpus callosum is cut, or a 'complete callosotomy' where the entire Corpus callosum is removed. The latter is usually performed if a partial callosotomy is insufficient in providing seizure control.

On average, patients experience a 70 to 80 percent reduction in their seizure frequency after a partial callosotomy and an 80 to 90 percent reduction after a complete callosotomy.

However, the main risk of Corpus callosotomy is the occurrence of 'Disconnection syndrome' - where there is a disruption in the communication between the two brain hemispheres. This results in the patient struggling to complete difficult tasks, name objects and drive.

Multiple Subpial Transections (MST)

This extremely rare surgical procedure is important for patients who have focal seizures originating in areas of the brain responsible for vital functions such as speech and movement - and hence those regions of the brain cannot be removed safely via alternative surgical means.

The brain fibres that have a role in vital functions run vertically, whereas, the brain fibres that are responsible for the seizures run horizontally.

Through MST, the horizontal fibres causing the seizures are cut ('transected'), to spread the seizures from spreading to other parts of the brain, and without affecting important brain functions. However, this does not stop seizures from occurring.

More information about MST can be found here.

Neurostimulation

Rather than surgically removing or disconnecting parts of the brain, devices can be implanted into patients in order to control their seizures through stimulating the brain in different ways. This treatment is extremely beneficial for patients with drug resistant epilepsy.

There are 3 main types of Neurostimulation: Deep brain stimulation (DBS), Responsive Neurostimulation and Vagus Nerve Stimulation (VNS).

1) Deep Brain Stimulation (DBS):

This form of Neurostimulation consists of 3 main components: the implanted pulse generator (IPG), the electrode (lead), and an optional extension.

The pulse generator (which is similar to a pacemaker) is implanted under the skin and on the chest wall, and it delivers continuous stimulation via the extension to the electrodes. The electrodes are placed by drilling holes in the skull, specifically above the epileptic origins in the brain.

The signals from the pulse generator help to stop arising seizures.

More information on DBS can be found here.

2) Responsive Neurostimulation:

Rather that providing continuous stimulation as seen in DBS, responsive neurostimulation records brain activity and seizure patterns, and delivers stimulatory signals only when it detects that a seizure is about to occur to stop the seizure.

So in simple words, it only sends signals in response to the detected epileptic activity.

Responsive neurostimulation consists of: an electric generator implanted in the skull, and electrodes that are placed on the regions where seizures begin.

Vagus Nerve Stimulation (VNS):

The VNS device consists of 2 components: an electric generator (placed over the chest and under the skin) and a stimulator lead wire (attached to the vagus nerve located in the neck).

The electric generator stimulates the vagus nerve on a set schedule, which sends signals to the brain to reduce seizures and their severity.

More information can be found here.

Below is a comparison between all 3 different types of Neurostimulation, highlighting other key important details:

Takeaway

Epilepsy surgery offers a vital alternative for patients with Drug-Resistant Epilepsy (DRE) who do not respond to Anti-Epileptic Drugs (AEDs). While the prospect of surgery may seem daunting due to the associated risks, it can significantly reduce or even eliminate seizures for many patients.

This article explores the various surgical options, from resective and disconnective procedures to advanced neurostimulation techniques. Understanding these options, along with their potential benefits and risks, empowers patients and clinicians to make informed decisions about managing epilepsy and improving quality of life.

References

Casanova, M.F. and Casanova, E.L. (2018). The Modular Organization of the Cerebral Cortex: Evolutionary Significance and Possible Links to Neurodevelopmental Conditions.

Children’s Hospital of Pittsburgh. (n.d.). Functional Hemispherectomy Procedure | UPMC Children’s Hospital. [online] Available at: https://www.chp.edu/our-services/brain/neurosurgery/epilepsy-surgery/types-of-surgery/hemispherectomy [Accessed 25 Aug. 2024].

Jagtap Clinic and Research Centre. (n.d.). How is the Deep Brain Stimulator system implanted? | Jagtap Clinic and Research Centre. [online] Available at: https://www.jagtapclinic.com/terms/how-is-the-deep-brain-stimulator-system-implanted/6779 [Accessed 30 Aug. 2024].

Kiriakopoulos, E., Cascino, G. and Britton, J. (2018). Types of Epilepsy Surgery. [online] Epilepsy Foundation. Available at: https://www.epilepsy.com/treatment/surgery/types#Multiple-Subpial-Transections-(MST) [Accessed 30 Aug. 2024].

Sheffield Children's (2022). Vagus nerve stimulation (VNS) - Resource Library - Sheffield Children’s NHS Foundation Trust. [online] Resource Library - Sheffield Children’s NHS Foundation Trust. Available at: https://library.sheffieldchildrens.nhs.uk/vagus-nerve-stimulation-vns/ [Accessed 30 Aug. 2024].

SickKids. (2024). SickKids implants the first Responsive Neurostimulation Device in Canada to treat drug-resistant epilepsy. [online] Available at: https://www.sickkids.ca/en/news/archive/2024/sickkids-implants-the-first-responsive-neurostimulation-device-in-canada-to-treat-drug-resistant-epilepsy/ [Accessed 30 Aug. 2024].

The University of Queensland (2017). Corpus callosum. [online] qbi.uq.edu.au. Available at: https://qbi.uq.edu.au/brain/brain-anatomy/corpus-callosum [Accessed 30 Aug. 2024].

Villines, Z. (2021). Epilepsy surgery: Types, success rates, recovery, and cost. [online] www.medicalnewstoday.com. Available at: https://www.medicalnewstoday.com/articles/epilepsy-surgery#types-of-surgery [Accessed 30 Aug. 2024].

WebMD (n.d.). Epilepsy and Functional Hemispherectomy. [online] WebMD. Available at: https://www.webmd.com/epilepsy/functional-hemispherectomy [Accessed 26 Aug. 2024].