Combination Of Frameless Navigation And Intraoperative Neurophysiology For Motor Cortex Stimulation.

Konstantin Slavin, MD, Keith Thulborn, MD, PhD, Univeristy of Illinois at Chicago, Chicago, IL, USA
kslavin@uic.edu

Motor cortex stimulation is one of the few available options for management of central deafferentation pain syndromes. Originally described only several decades ago for the treatment of thalamic and trigeminal pain syndromes, this non-destructive procedure is gradually gaining popularity among neurosurgeons and pain specialists. Recently, we began using a combination of computer-guided navigation and intraoperative electrophysiological monitoring for localization of the motor cortex in patients with medically intractable pain following a stroke or surgical intervention. The pain involved one side of body or face contralateral to the infarction or ipsilateral to surgical procedure; the patients did not respond to medical management including a trial of intrathecal opioids. The motor cortex was initially identified using a functional MRI on 3-Tesla scanner; this information was then used during intraoperative computer-aided navigation with a frameless guidance system. In order to further verify location of the motor cortex, we used epidural recording of the somatosensory evoked potentials after a small craniotomy was made under general anesthesia. Reversal of the polarity of the N20 peak indicated the line separating the primary motor and sensory cortical areas. The quadripolar electrode(s) (Medtronic) was then positioned over the motor cortex. During the trial, the pain relief was obtained with bipolar stimulation below the threshold of motor stimulation. There were no stimulation-induced paresthesias, the pain relief from the stimulation was almost immediate and lasted for few minutes after the stimulation was stopped. After a weeklong trial the electrode(s) was internalized under the general anesthesia. Using this combination of functional MRI, image-guided computer navigation, and intraoperative electrophysiological testing, we were able to precisely localize the primary motor cortex and subsequently achieve excellent pain relief in patients with medically intractable deafferentation pain. We present the details of our technique, report an illustrative case and discuss general aspects of the motor cortex stimulation procedure. The motor cortex stimulation may be an option for patients with chronic pain syndromes due to strokes, post-surgical procedures and other deafferentative conditions.

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