VISUALASE: epilepsy surgery with the laser catheter

Epilepsy patients are currently treated with either medication or surgical options. The aim is to remove the distinct regions of the brain that cause epileptic seizures. Laser ablation for epilepsy is a new, catheter-based surgical procedure that is now also available in Europe, preventing patients from having to undergo open brain surgery.

In this MEDICA-tradefair.com interview, Prof. Jürgen Voges talks about the "VISUALASE" (manufactured by Medtronic) surgery treatment, explains how MRI technology is used during the surgery and describes the patients who are good candidates for this option.

Prof. Voges, what is "VISUALASE MRI-Guided" Laser Ablation technology?

Prof. Jürgen Voges: This laser-based procedure allows us to ablate various morphological pathologies of the brain in real-time by using heat energy and magnetic resonance imaging (MRI) guidance. These include brain tissue mutations that cause epileptic seizures. The "VISUALASE" system has been used in the US since 2007 and has won CE Mark approval in March 2018. We used it to treat the first epilepsy patient in Germany in March of this year.

Apart from the treatment of epilepsy, the laser can also be used to remove small, well-differentiated tumors. We have treated epilepsy by using radiofrequency thermal ablation probes for some time. However, their application is limited when it comes to treating larger areas, and this process also does not facilitate real-time MRI monitoring during treatment. We initially decided to treat epilepsy since we have already gained a lot of experience in this area using radiofrequency thermal ablation.

How does the surgery work?

Voges: Using a stereotactic approach, we first place the laser probe in the patient's brain. After the surgery, the patient is moved to the MRI scanner. We first conduct a pre-ablation scan before we remove the target tissue. We raise the temperature of the tissue to no more than 40 degrees Celsius. Free water molecules are created when we deliver energy to the tissue via the laser and heat it up. They register via special MRI sequences. This information is used to create an image that displays the varying temperatures in different colors.

We use the image changes at 40 degrees as the checkpoint for the actual ablation, for which we heat the tissue to the targeted range of 43-57 degrees. The temperature change is monitored on the MRI image. By retracting or advancing it, we can then reposition the laser to another location and first conduct a pre-ablation scan and subsequently make the targeted ablation. We repeat this process until the area that is causing the epileptic seizures is detached from the surrounding, healthy brain tissue.

The patient remains in the MRI unit the entire time. We use a ceramic stereotactic frame that has no negative impact on the MRI images or thermal maps. This allows us to control the patient position. Theoretically, we could also completely change the position of the probe.

The description of this procedure also shows that you need the knowledge and expertise of various medical specialties (neurosurgery, anesthesiology, MRI physics, and neuroradiology) to guarantee a smooth ablation process.

How does this procedure differ from earlier thermal ablation systems?

Voges: This diode laser emits at a wavelength of 980 nanometers. It essentially has the same problems as previous laser thermal ablation: if we apply too much energy, it can result in uncontrolled tissue damage. However, this laser probe uses a special catheter with a continuously circulating saline solution. This cools the laser probe and allows us to heat larger volumes without deflagration, unlike previous probes.

Which patients are the best candidates for this type of treatment?

Voges: The best candidates are patients with a variety of pathologies that can cause epilepsy. This includes epilepsy involving the temporal lobe (with or without hippocampal sclerosis), periventricular nodular heterotopia, hamartomas, cavernomas and focal cortical dysplasia. In certain instances, these changes can also be treated and removed via conventional neurological surgery or resection. In other cases, they are located in functionally critical brain regions, making them difficult to reach by using neurosurgical resection, thus increasing the risk of adverse effects.

For tumors where surgical removal may prove difficult, I prefer stereotactic brachytherapy, i.e., local radiation therapy with a stereotactically implanted radiation source. From a biological perspective, it is conceivable that this type of radiation therapy results in beneficial side effects at the edge of the tumor, which locally boost the immune system for example. It remains to be seen how the laser probe fares in comparison.

What are the advantages compared to open surgery?

Voges: Needless to say, it takes far less surgical effort to implant the laser probe. For patients who are generally surgical candidates but have reservations about conventional resection, laser thermal ablation might be a viable alternative.

Right now it seems that the effectiveness and specifically the seizure reduction is comparable to open surgery. Having said that, it is still unclear whether laser ablation has fewer severe side effects compared with conventional temporal lobe resection. We will only be able to assess both facets over the course of time once a sufficient number of patients has received laser ablation treatment.