June 19, 2021
Mayo Clinic is investigating the use of magnetic resonance (MR)-guided focused ultrasound as an incisionless treatment for medication-refractory focal epilepsy. The thermoablative therapy has the potential to reduce or eliminate seizures for individuals whose epilepsy doesn't respond to medication without requiring any drilling through the skull.
"The focused ultrasound energy kills highly selected areas that we can select on imaging — disrupting the epilepsy network without surgical resection of the lesion," says Jamie J. Van Gompel, M.D., a neurosurgeon at Mayo Clinic's campus in Rochester, Minnesota. "Our hope is eventually to make many of these patients seizure-free without ever having to make an incision."
MR-guided focused ultrasound has been used to treat movement disorders, such as essential tremor. Mayo Clinic's study of the technology for the treatment of focal epilepsy is part of a multicenter clinical trial. Patient enrollment in the trial is by invitation only.
The technology focuses ultrasound waves through the skull to treat deep areas of the brain. MR guidance helps identify and target the tissue to be permanently treated and tracks the treatment in real time.
Ultrasound ablation of the hippocampal tail and fimbria
A. Pre-procedural imaging known as magnetization prepared rapid acquisition gradient echo (MPRAGE) registered to CT shows the calvarium (green) with a prior craniotomy (red) marked as a no-pass zone for ultrasound. The hippocampal tail remnant is outlined in magenta (black arrow). B. Intraprocedural MR thermometry shows the hippocampal tail target (yellow circle and crosshairs). C. Immediate post-procedural diffusion-weighted imaging shows the ablated hippocampal tail with bright signal (black arrow).
Mayo Clinic's first trial participant recently had MR-guided focused ultrasound ablation in a hippocampal remnant that remained after temporal lobectomy. "The patient has had a substantial reduction in seizures and is very happy with the results thus far," Dr. Van Gompel says.
He notes that MR-guided focused ultrasound potentially might be used to perform:
- Hippocampal disconnection, to prevent seizure outflow from the temporal lobe to the rest of the brain
- Thalamic ablation, for patients who previously responded to procedures that stimulated the anterior nucleus of the thalamus
- Ablation of hypothalamic hamartomas
- Ablation of cortical dysplasias
About one-third of people with epilepsy have medically refractory seizures. In the past, treatment relied on surgical removal of lesions in areas such as the temporal or frontal lobe or insular cortex.
Incisionless treatments require expert imaging to locate seizure-origin sites and to guide the performance of these interventions. Mayo Clinic's radiologists have extensive experience with ablative treatments elsewhere in the body and helped guide the adoption of those technologies for use in the brain.
"We have partnered with our neurosurgeons from the beginning of laser and focused ultrasound treatments in the brain," says Timothy J. Kaufmann, M.D., M.S., a neuroradiologist at Mayo Clinic in Minnesota. "Our experience with focused ultrasound thalamotomy has shown us that we can be very precise with our imaging and use of the ablation device."
Dr. Kaufmann notes that current technology limits the use of MR-guided focused ultrasound to lesions relatively close to the midline. "Because of the geometry and physics of the device, those are the areas where we can raise temperatures to a therapeutic level and induce ablation. However, recent experimental advances in the focused ultrasound equipment have extended the reach of this device to a degree," he says. "Small lesions also might be more suited to this treatment because it would take too much time to treat very large lesions, and the efficiency of brain heating diminishes over the course of an ablation."
The investigation of MR-guided focused ultrasound is part of Mayo Clinic's commitment to providing the least invasive care that will be effective for patients with refractory epilepsy. "We work on a variety of platforms to treat epilepsy without large cranial incisions," Dr. Van Gompel says. "Collaboration with our colleagues in Neuroradiology is critical to providing these treatment options for our patients."
For more information
InSightec. MR-Guided Focused Ultrasound in the Treatment of Focal Epilepsy (EP001). ClinicalTrials.gov.