Nathan R. Selden, MD, PhD
Chair, Department of Neurological Surgery, Oregon Health & Science University (OHSU)
Campagna Chair of Pediatric Neurosurgery, Doernbecher Children’s Hospital
Watching a young child have a seizure is heartbreaking and frightening, especially for parents. Fortunately, modern medicine has had a profound impact on this problem. Since Sir Victor Horsley removed a brain seizure focus in 1886, neurosurgery has evolved to dramatically improve the health and well-being of many epilepsy patients.
Today, two major trends are driving profound change in epilepsy surgery. The first is a major shift in the demographics and timing of care, which has been building steadily for over a decade. The second, more recent and even more sudden, is a complete rethinking of the topographical approach to epilepsy surgery for diagnosis and treatment. Both of these trends are having a substantial impact on the work of pediatric neurosurgeons and the hospitals in which they practice.
Historically, neurologists were hesitant to refer children for invasive epilepsy monitoring and surgery based on the hope that many cases of pediatric epilepsy would resolve spontaneously with development. Decades of data from longitudinal follow-up of these patients has shown instead that, with rare and well-defined exceptions, most pediatric epilepsy patients who fail initial therapy with two anti-convulsant medications will continue to suffer from epilepsy into adulthood. The effects of prolonged epilepsy and chronic anti-convulsant medication therapy on these patients are generally profound and often devastating to neurodevelopment, intellectual achievement, independence as an adult and quality of life. Fortunately, our pediatric neurology colleagues have responded vigorously, identifying and referring children with medically refractory epilepsy early to centers capable of a full range of diagnostic, medical and surgical interventions.
Recently, the care given to children at these major, accredited epilepsy centers has also changed dramatically, taking advantage of new technology that helps pediatric epilepsy surgeons access remote areas of the brain. Epilepsy is often a limbic system disease. Tucked largely into the mesial temporal, parietal and frontal lobes, and the insula, the limbic system is relatively difficult to access using traditional open surgical approaches along the hemispheric convexity. Children have a very high incidence of epilepsy secondary to malformations of cortical development (MCD’s) that are often more widespread than epileptogenic lesions in adults, and also more likely to occur outside the temporal lobe. Because of this, determining the location and extent of epileptogenic cortex in children using traditional invasive mapping techniques — such such as subdural grids and strips — has been particularly challenging. As a result, failure rates for pediatric epilepsy surgery have traditionally been significant, particularly in widespread MCD’s and in extra-temporal epilepsy, which are more common. The most frequent reason for poor seizure control after surgery in many pediatric patients is the presence of residual epileptogenic tissue. Often, topographically difficult to access limbic areas, particularly prone to seizures, remain undetected and untreated.
Recent and dramatic advances in surgical technology are helping to mitigate these challenges to pediatric epilepsy surgery. The most important recent advances combine point-to-point navigation technology, advanced imaging and robotic surgical control to minimally invasively access widespread mesial cortical and limbic structures. This approach allows implantation of traditional depth electrodes to detect and map even deep and remote seizure foci, followed by delivery of laser energy to ablate and treat them.
Depth electrode placement is not new. Modern MRI-guided neuro-navigation has supported hippocampal and other mesial hemispheric depth electrode placement, for example, for decades (see Figure 1). Using this approach for children with potential widespread MCDs was far too complex using traditional stereotactic frame-based depth electrode placement. New robotic technology, like that we have acquired for OHSU and Doernbecher Children’s Hospital, radically expands the practicality and safety of placing well over a dozen depth electrodes per hemisphere, each monitoring mesial and superficial cortical sites along a single trajectory. In addition, simultaneous bilateral hemispheric monitoring has become much more feasible where indicated by initial imaging and surface mapping studies.
When invasive mapping identifies mesial temporal or other deep hemispheric or limbic seizure foci, ablation of this deep tissue can now also be done more effectively with minimally invasive, robotic-assisted techniques. The same robot used to place depth electrodes is ideal for inserting a stereotactic probe capable of delivering laser energy to ablate the offending seizure focus thermally. At Doernbecher and OHSU, we perform these procedures in a 3-Tesla intraoperative MRI scanner, allowing real-time imaging of the thermal bloom resulting from the laser treatment. This approach provides exquisite control of the anatomical location, size and shape of the ablative lesion, without ever leaving the sterility and safety of a fully equipped neurosurgical operating room (see Figure 2).
Bringing this amazing technology to bear, we can now treat a patient — who would have once had two open craniotomies — with a series of tiny punch incisions and minimally invasive access for both diagnosis and curative therapy, often in a single, very short hospital stay. Most importantly, even though these approaches are minimally invasive, they offer more widespread access to the relevant cortical and limbic anatomy, and thus the promise of even higher cure rates for patients suffering from severe and medically refractory epilepsy.
Continual innovation by scientists, engineers and pediatric neurosurgeons is providing dramatic new hope to children who were previously ineligible for a chance at a surgical cure of their epilepsy. Parents now have options for powerful, minimally invasive therapies that were unthinkable only a few years ago. These advances are also generating renewed energy and optimism amongst the community of physicians caring for children with epilepsy.
Editor’s Note: We encourage everyone to join the conversation online by using the hashtag #PedsNeurosurgery.