Stereotactic radiosurgery for medically refractory non-lesional epilepsy: A case-based Radiosurgery Society (RSS) practice review.

Introduction: Medically refractory epilepsy (MRE) occurs in about 30 % of patients with epilepsy, and the treatment options available to them have evolved over time. The classic treatment for medial temporal lobe epilepsy (mTLE) is anterior temporal lobectomy (ATL), but an initiative to find less invasive options has resulted in treatments such as neuromodulation, ablative procedures, and stereotactic radiosurgery (SRS). SRS has been an appealing non-invasive option and has developed an increasing presence in the literature over the last few decades. This article provides an overview of SRS for MRE with two example cases, and we discuss the optimal technique as well as the advantages, alternatives, and risks of this therapeutic option.

Cases: We present two example cases of patients with MRE, who were poor candidates for invasive surgical treatment options and underwent SRS. The first case is a 65-year-old female with multiple medical comorbidities, whose seizure focus was localized to the left temporal lobe, and the second case is a 19-year-old male with Protein C deficiency and medial temporal lobe sclerosis. Both patients underwent SRS to targets within the medial temporal lobe, and both achieve significant improvements in seizure frequency and severity.

Discussion: SRS has generally been shown to be inferior to ATL for seizure reduction in medically refractory mTLE. However, there are patients with epilepsy for which SRS can be considered, such as patients with medical comorbidities that make surgery high risk, patients with epileptogenic foci in eloquent cortex, patients who have failed to respond to surgical management, patients who choose not to undergo surgery, and patients with geographic constraints to epilepsy centers. Patients and their physicians should be aware that SRS is not risk-free. Patients should be counseled on the latency period and monitored for risks such as delayed cerebral edema, visual field deficits, and radiation necrosis.