Epilepsy becomes refractory in roughly one-third of newly diagnosed patients.1 Surgical resection is an option for some of these patients, but is problematic when the seizure focus resides in eloquent cortex (such as language, motor, or visual areas).2 For these patients, nondestructive neuromodulatory operations, such as vagus nerve stimulation (VNS), deep brain stimulation (DBS), and responsive neurostimulation (RNS), are alternative therapies that have generated increasing interest in the past decade.3 Yet, one of the original techniques for treating eloquent seizure foci is sometimes overlooked: multiple subpial transections (MST).
MST were first described by Frank Morrell and colleagues in 19894 as a means of treating refractory epilepsy when the focus lay in what they termed unresectable cortex.4 The technique uses a small metal wire with a right-angle hook at its end, extending ∼4 mm. This hook is inserted into 1 side of a cortical gyrus, as close to the sulcus as possible, and then driven to the far side subcortically, toward the next sulcus. The bent end of the wire is subsequently raised to the pial surface, and the hook dragged under the pia back to the wire’s entry point. This maneuver severs intracortical fibers along the wire’s course, but spares subcortical white matter and U-fibers. Cuts are made perpendicular to the gyrus, from one sulcus to the other, and repeated roughly every 5 mm. The extent of the cuts spans the unresectable epileptic focus. The concept behind this technique is to prevent ictal activity from spreading throughout the focus via intracortial connections, but preserve the major subcortical inputs and outputs of the eloquent region. In their initial study of 20 patients, Morrell et al4 reported a seizure freedom rate (Engel class I) of 55% with no significant induced deficits.
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