What Is Laser Ablation’s Role in Treating Hippocampal Epilepsy?

PHILADELPHIA—Among patients with hippocampal epilepsy, MRI-guided laser ablation of the hippocampus and amygdala may provide good seizure outcomes, improved cognitive outcomes, and fewer surgical complications, compared with anterior temporal lobectomy, according to research presented at the 69th Annual Meeting of the American Epilepsy Society. In addition, patients who decline to have an open resection may be willing to undergo laser ablation, said John W. Miller, MD, PhD.

John W. Miller, MD, PhD

“We have found that laser ablation is a disruptive technology. It’s disruptive in a good sense because it has taken over a good part of our epilepsy surgery practice,” said Dr. Miller, Director of the University of Washington Regional Epilepsy Center and Professor of Neurology and Neurological Surgery in Seattle.

In anterior temporal lobectomy, surgeons access the hippocampus by removing the front end of the temporal lobe, which often is not responsible for causing seizures, and the resection may have cognitive consequences.

MRI-guided selective laser ablation of the amygdala and hippocampus is designed to prevent injury to the adjacent temporal cortex and white matter. It entails a posterior approach to the target tissue through a small burr hole in the occipital skull. A laser fiber assembly heats the target, and real-time temperature monitoring and estimates of thermal damage ensure that the target tissue is ablated. The FDA has approved laser ablation devices (ie, Visualase in 2010 and NeuroBlate in 2013) for thermocoagulating brain tissue, although not specifically for treating epilepsy.

Naming and Recognition Tests

In a study published in 2015, Daniel L. Drane, PhD, and colleagues found that patients with temporal lobe epilepsy who underwent laser ablation of the amygdala and hippocampus declined less on measures of naming and object recognition, compared with patients who underwent open resection. Dr. Drane, Associate Professor of Neurology and Pediatrics at Emory University in Atlanta, presented additional data at the meeting that suggest that patients who undergo laser ablation also may have improved episodic memory outcomes, compared with patients who undergo open resection. The rationale for performing laser ablation is based on those cognitive outcome findings, Dr. Miller said.

“With dominant anterior lobectomies, there are naming deficits, but with nondominant resections, there are recognition deficits. And often these are not well detected by standard testing procedures,” Dr. Miller said. “If the seizure outcome [for laser ablation] is reasonable, as it appears to be for hippocampal epilepsy, the laser ablation would be preferred, particularly if the patient was left-sided or [in] those cases with higher risk of poor cognitive outcome from anterior temporal lobectomy.”

Seizure Outcomes for Laser Ablation

Dr. Miller presented data that Robert E. Gross, MD, PhD, Professor of Neurosurgery, Neurology, Biomedical Engineering, and Neuroscience at Emory University, had compiled from centers that have performed laser ablation on significant numbers of patients. Of 130 patients who had laser ablation for mesial temporal lobe epilepsy without other lesions or pathology and at least one year of follow-up, 62% had an Engel Class I outcome at 12 months. In patients with hippocampal sclerosis, 66% had a Class I outcome after the procedure. These data show that seizure outcomes for laser ablation are “in the ballpark” of those for anterior temporal lobectomy, Dr. Miller said.

In a series of 325 patients in Australia who underwent standard anterior lobectomy, McIntosh et al found that the one-year seizure-freedom rate was 61%. The seizure-freedom rate at 10 years was 41%. In a subgroup of patients with hippocampal sclerosis, 67.7% of patients were seizure-free at one year, and 47% were seizure-free at 10 years. Other series reported similar results, Dr. Miller said.

Case series for selective amygdalohippocampectomy, another surgical approach designed to reduce collateral damage, suggest that seizure-freedom outcomes are similar to those for anterior temporal lobectomy. Two meta-analyses found that seizure-freedom rates are about 7–8% lower for selective amygdalohippocampectomy than for anterior temporal lobectomy.

Cognitive outcomes for selective amygdalohippocampectomy are difficult to assess because series may use different operative approaches and test batteries. “Overall, the majority of studies, but not all, show some superiority for the selective procedure over the anterior temporal lobectomy,” Dr. Miller said.

Dr. Miller hypothesized that laser ablation cannot be more effective in treating seizures than selective amygdalohippocampectomy. “In practice, the anterior temporal lobectomy may be preferred in situations were there’s less cognitive or perioperative risk,” he said. “For example, somebody who has severe baseline left-sided cognitive dysfunction would be at lower risk to develop worsening of that function. You might consider anterior temporal lobectomy because of its possible higher efficacy.”

Perioperative Complications