Background

Epilepsy is a common chronic neurological disorder characterized by recurrent unprovoked seizures. These seizures are transient signs and/or symptoms of abnormal, excessive or synchronous neuronal activity in the brain. While more likely to occur in young children or people over the age of 65 years, epilepsy can occur at any age. Epilepsy is usually controlled, but cannot be cured, with medication.

Epilepsy surgery is an option for patients whose seizures remain resistant to treatment with anticonvulsant medications and who also have symptomatic localization-related epilepsy: a focal abnormality that can be located and therefore removed or inactivated. Mesial temporal lobe epilepsy (TLE) is the most frequent cause of medically intractable epilepsy in adults. TLE consists of neuronal loss, atrophy and gliosis within the amygdala-hippocampus and limbic system. The most common type of epilepsy surgery is the anterior temporal lobectomy, or the removal of the front portion of the temporal lobe including the amygdala and hippocampus. Surgery for temporal lobe epilepsy is effective and durable. However, invasive brain surgery entails small but real risks of hemorrhage, infection and other complications despite contemporary MR-guided techniques.

Current State

Focused ultrasound may someday be used in the treatment of temporal lobe epilepsy (TLE). One technical hurdle that remains is the ability to safely ablate epileptogenic brain tissue close to (<2.5 cm) the skull base. Excessive heating of non-targeted brain tissue may occur when the target is close to bone, given that the bone absorbs approximately 50 times the ultrasound energy of soft tissue, with significant resultant heating. In addition, a safe treatment paradigm must allow for protection of the optic tract and other cranial nerves and important blood vessels in the region.

If these technical hurdles can be overcome, a clinical trial of focused ultrasound for temporal lobe epilepsy may be indicated. Given the significant risk of loss of verbal fluency after dominant temporal resections, the ROSE trial has been devised to compare selective temporal lobe resections with Gamma knife radiosurgery in the treatment of TLE. Results of that study may impact on the design of a focused ultrasound trial. Focused ultrasound would have a distinct advantage over Gamma knife radiosurgery in causing a fairly rapid cessation of seizures and in not involving ionizing radiation.