Seizure outcomes in nonresective epilepsy surgery: an update

Abstract

In approximately 30 % of patients with epilepsy, seizures are refractory to medical therapy, leading to significant morbidity and increased mortality. Substantial evidence has demonstrated the benefit of surgical resection in patients with drug-resistant focal epilepsy, and in the present journal, we recently reviewed seizure outcomes in resective epilepsy surgery. However, not all patients are candidates for or amenable to open surgical resection for epilepsy. Fortunately, several nonresective surgical options are now available at various epilepsy centers, including novel therapies which have been pioneered in recent years. Ablative procedures such as stereotactic laser ablation and stereotactic radiosurgery offer minimally invasive alternatives to open surgery with relatively favorable seizure outcomes, particularly in patients with mesial temporal lobe epilepsy. For certain individuals who are not candidates for ablation or resection, palliative neuromodulation procedures such as vagus nerve stimulation, deep brain stimulation, or responsive neurostimulation may result in a significant decrease in seizure frequency and improved quality of life. Finally, disconnection procedures such as multiple subpial transections and corpus callosotomy continue to play a role in select patients with an eloquent epileptogenic zone or intractable atonic seizures, respectively. Overall, open surgical resection remains the gold standard treatment for drug-resistant epilepsy, although it is significantly underutilized. While nonresective epilepsy procedures have not replaced the need for resection, there is hope that these additional surgical options will increase the number of patients who receive treatment for this devastating disorder-particularly individuals who are not candidates for or who have failed resection.

Keywords: Brain stimulation; Disconnection; Epilepsy surgery; Review; Seizure outcome.

Figure 1. Stereotactic laser ablation (SLA) for mesial temporal lobe epilepsy

A–C) Shown are T1-weighted MRI axial (A), sagittal (B), and coronal (C) images showing during laser probe placement along the axis of the left hippocampus, prior to SLA in a patient with mesial temporal lobe epilepsy. D–F) Contrast-enhanced T1-weighted MRI axial (D), sagittal (E), and coronal (F) images obtained approximately 5–10 minutes after thermal ablation of mesial temporal lobe structures, with contrast enhancement seen in the region of ablation. Lesioning is performed with real-time MRI thermal measurements. A: anterior; L: left; P: posterior; R: right.

Figure 2. Development of radiologic changes in a patient with mesial temporal lobe epilepsy treated with a 24-Gy dose Gamma Knife stereotactic radiosurgery (SRS)

FLAIR (A–E) and T2 (K–O) hyperintensity appeared within the medial temporal lobe beginning by the 10th postoperative month and peaked in intensity at 12 months, corresponding to a decline in the proportion of patients experiencing complex partial seizures. Contrast enhancement (F–J) followed a similar time course, except that it preceded T2 changes and diminished quickly after months 10–12. Enhancement was typically ring-enhancing and centered over the target region. Figure and legend reproduced with license and permission from Chang et al. [17].

Figure 3. The responsive neurostimulation device (RNS)

A) Shown is a NeuroPace RNS device configured for stimulation of one four-contact depth electrode and one four-contact strip electrode. B) Artistic depiction of implanted RNS device, including a depth electrode and a cortical strip electrode. Images provided courtesy of NeuroPace.