Stereoscopic Monitoring Technique for Motor Area Tumors.

BACKGROUND: The balance between comprehensive intraoperative neurophysiological monitoring (IONM) for both upper and lower limbs while ensuring the reliability of motor evoked potentials (MEPs) is paramount in motor area surgery. It is commonly difficult to obtain good simultaneous stimulation of both upper and lower limbs. A series of factors can bias MEP accuracy, and inappropriate stimulation intensity can result in unreliable monitoring. The presented IONM technique is based on the concurrent use of both transcranial and cortical strip electrodes to facilitate simultaneous monitoring of both upper and lower limbs at optimized stimulation intensities to increase IONM accuracy during motor area surgery. METHODS: Ten nonconsecutive motor area tumors were studied. Good visualization of both limbs was observed in the series at a low amperage (1.2 mA from the strip electrode and 165.3 mA from the transcranial electrode). RESULTS: Our analysis confirms concordance between the IONM data and postoperative outcomes. An MEP reduction >20% and >50% correlated with postoperative modified Rankin scale score changes without false-negative IONM findings. CONCLUSIONS: The technique was demonstrated to be accurate in providing a good simultaneous neurophysiological evaluation of both upper and lower limbs with an optimized and stimulation amplitude. The technique results in a low encumbrance of electrodes in the surgical field. Our results have confirmed the "proof of concept," its reliability and feasibility.

Methods and Principles of the Intraoperative Neurophysiologic Monitoring in Neurosurgery.

Intraoperative neurophysiologic monitoring (IONM) is an innovation introduced in neurosurgery in the past decades. It aims to support and guide the neurosurgeon to obtain the best surgical result possible, preventing the occurrence of neurological deficits. The somatosensory evoked potentials (SSEP) assess the integrity of the sensory pathways monitoring the dorsal column-medial lemniscus pathway during spine and cerebral surgery. Motor evoked potentials (MEPs) provide information on the integrity of the motor pathway monitoring the efferent motor pathways from the motor cortex to the muscle through corticospinal (or corticobulbar) tracts. Free-running EMG is the standard technique to monitor peripheral nerves, roots, or cranial motor nerves during surgery. Intraoperative EMG signals are activated during cranial motor nerves damaging or after an irritative stimulus. The duration, morphology, and persistence of EMG reflects the severity of neural injury. Nerve mapping consists of recording muscle activations given by direct nerve stimulation. This technique makes use of a stimulation probe available to the neurosurgeon which allows administering current directly to the nervous tissue (nerves, roots, etc.). Intraoperative neurophysiological monitoring (IONM) represents the standard of care during many procedures, including spinal, intracranial, and vascular surgeries, where there is a risk of neurological damage. Close communication and collaboration between the surgical team, neurophysiologist, and anesthesiologist is mandatory to obtain high-quality neuromonitoring, thus preventing neurologic injuries and gaining the best surgical "safe" results.