Motor Cortex Stimulation (transdural electrical stimulation of the precentral gyrus)
Motor cortex stimulation (MCS) is a surgical option reserved for patients with trigeminal neuralgia pain, which proves difficult to alleviate. As the name suggests this procedure involves stimulation of the region of the outer portion of the brain (motor cortex) most immediately involved in movements of the face, neck, trunk, and arm and leg.
Pre-operatively a specific region (the precentral gyrus), is located by electrode recording, three-dimensional magnetic resonance imaging (MRI) of the brain surface with a reference grid attached to the patient’s skin or by a stereotactic frame-based MRI. Operatively, usually under general anesthesia a craniotomy is performed and a quadripolar plate electrode is inserted into the space outside the tough fibrous membrane covering the brain (epidural space) and above the precentral gyrus. The facial motor region is stimulated using the grid electrode and the face observed for indications of muscular contraction. Intraoperative electrode stimulation may result in complete pain relief. A longer trial stimulation is however usual before permanent implantation of a pulse generator.
The electrode is tested as soon as the patient is fully awake and continues until the patient can consistently confirm that stimulation reduces the preoperative pain by at least 50%. A second craniotomy, also under general anesthesia, is required for permanent implantation of a pulse generator. The pulse generator is usually positioned in a pocket in the upper chest wall and permanently connected to the electrode.
Risk of Motor Cortex Stimulation
Procedure-related risks include; intraoperative seizures, stimulator/pulse generator-pocket infection, an accumulation of blood between the skull and the dura (epidural hematoma), fluid release into the dura (subdural effusion), gradual loss of benefit, and painful stimulation.