Pediatric Section Update: Innovation in the Surgical Treatment of Epilepsy
The surgical treatment of pediatric epilepsy is currently undergoing a transformation in the neurosurgical approaches to diagnostic evaluation and therapeutic treatment. Several techniques have been innovated and modified with a common theme of less invasive procedures that provide comparable results with quicker recovery. Many innovations are made possible by advances in technology that either improve a previous technique, such as robotic guidance for stereo-electroencephalography (SEEG), or introduce a new modality for achieving a similar result, as with laser interstitial thermal therapy (LITT) for focal ablation. Other techniques have also continued to be modified to be performed through a minimally invasive approach. Collectively, these advances set the stage for a very exciting time for pediatric neurosurgeons to be caring for patients with epilepsy.
SEEG has seen tremendous growth among pediatric neurosurgeons throughout North America in recent years. Even though SEEG has been well described and routinely used in Europe for several decades, the introduction of surgical robotics and high-quality CT angiography has led to greater accuracy and shorter procedure times for placing SEEG electrodes. In addition to the numerous cases series and, more recently, a meta-analysis in the adult literature, two recent reports on institutional pediatric experiences have further supported the safety of SEEG (Goldstein, et al 2018 and Ho, et al 2018). Both reports included >20 pediatric patients and report no major complications (1 asymptomatic extra-axial hemorrhage) and 92-95% went on to a therapeutic surgical procedure. Both made use of the ROSA surgical robot for stereotactic placement and MRI or CT angiography to avoid vasculature when planning electrode trajectories.
Neuromodulation in Pediatric Patients
Resection, disconnection or ablation of the seizure onset zone remains the primary goal of most pediatric epilepsy surgery. However, neuromodulation for non-localized epilepsy continues to make significant advances. Vagal nerve stimulation (VNS) is the most commonly employed method for reducing seizure burden by modulating the central nervous system through the peripheral stimulation of the vagus nerve. VNS therapy is supported by a large number of well-orchestrated studies that led to initial FDA device approval in 1997 for patients older than 12 years of age. Recently, additional studies have included younger patients demonstrating similar efficacy and low complication rates. This led to recent FDA approval for children at age 4 years and greater.
Deep brain stimulation for movement disorders is an established procedure that has recently seen adoption for non-focal epilepsy. DBS for epilepsy has been reported most in adult populations with studies like the SANTE (Stimulation of the Anterior Nuclei of the Thalamus) trial. Recently a systematic review by Yan, et al, was published in 2018 that identified 40 pediatric cases across 21 reports in the literature. Overall, 85% of cases reported seizure reduction and 12.5% achieved seizure freedom with DBS. These cases spanned a wide range of targets, including the centromedian nucleus of the thalamus, anterior nucleus of the thalamus, subthalamic nucleus, hypothalamus, mammillothalamic tract, and the zona incerta. Although the results are exciting, much work is still needed to determine the optimal patient selection and the best target for stimulation.
Interestingly, one innovative case study by Kokoszka, et al (2018), made use of the responsive neurostimulation (RNS, NeuroPace) device for both cortical and deep brain responsive stimulation. Their configuration placed a surface lead on the temporal neocortex and a second lead in the ANT. By detecting seizures from the neocortex and stimulation on both the temporal surface and ANT, they achieved closed-loop corticothalamic stimulation resulting in a 50% reduction in seizure frequency. The relative strengths of closed-loop stimulation through RNS compared to open-loop neuromodulation devices like VNS and DBS are not fully resolved. However, all of these modalities carry great potential for intervention in non-focal medically refractory epilepsy.
Innovative Approaches to Surgical Disconnection
Beyond neuromodulation, advances in reducing surgical morbidity are being achieved by adopting endoscopy and LITT for hemispherotomy and corpus callosotomy. Chandra, et al (2018), published a comparison of endoscopic assisted and open hemispherotomy in pediatric patients, with detailed operative photographs and an accompanying surgical video. They describe a hybrid approach using an operating scope of similar diameter to an exoscope, which is typically held outside of the surgical cavity but positioned intracranially at a distance to facilitate a wider field of view. They also used the ROSA surgical robot for precise positioning of the endoscope. A similar endoscopic approach to hemispherotomy was also reported by Wagner, et al (2018). They detail the technical approach in a cadaveric study followed by the successful clinical translation of the procedure performed in 2 pediatric patients.
Corpus callosotomy alone, or as a step of a functional hemispherotomy can similarly be achieved via an endoscopic- assisted technique. Endoscopic approaches have been described with variations in approach from the vertex (Sood, et al, 2015), similar to endoscopic hemispherotomy techniques, as well as a posterior approach that requires less interhemispheric dissection (Sood, et al, 2016).
Alternatively, LITT is being increasingly adopted at institutions across the country. While LITT is used more frequently for tumors or lesional ablation, it has also been described for achieving corpus callosotomy with a much less invasive procedure. LITT is also referred to as magnetic resonance-guided LITT (MRgLITT) or as MRI-guided laser interstitial thermal ablation (MTLA) and is FDA approved to necrotize or coagulate soft tissue. Therefore, by placing a laser fiber along the length of the corpus callosum, surgical disconnection can be achieved by ablating tissue along the length of the trajectory. Palma, et al (2019), describe their approach to LITT callosotomy in 3 patients (2 of which are pediatric) with > 3 years follow up. Variations in laser fiber trajectory are used depending on the specific anatomic considerations.
These and many other innovative approaches to the neurosurgical treatment of epilepsy are making tremendous strides to improving the care of pediatric patients with medically refractory epilepsy (MRE). It is well known that significant numbers of patients with MRE never undergo evaluation at a comprehensive epilepsy center where surgical interventions can be considered. By advancing the field with greater options for surgical treatment, particularly less invasive options that improve discomfort, shorten hospital stay, and reduce risks, we have great potential to increase the accessibility and acceptability to patients, parents, and referring providers to seek appropriate neurosurgical evaluation. The studies above suggest pediatric neurosurgeons are contributing to this goal by surgical innovations that make use of evolving technology.