Demonstration of cerebral plasticity by intra-operative neurophysiologicalmonitoring: Report of an uncommon case

It has been postulated long ago that "eloquent" areas shift their location in patients with arteriovenous malformations (AVM). Obviously the "motor re gion" in not located in the precentral gyrus in a patient with an AVM in th e "motor region". We report on the case of a 15-year old boy with an AVM in the left sensorim otor cortex, in whom intra-operative mapping showed an inexcitability of th e precentral gyrus, while stimulation of the cortex anterior to the primary motor cortex elicited motor responses. This indicates that motor function was translocated from the primary to the supplementary motor cortex. Surger y was performed under general anaesthesia. Neurophysiological monitoring wa s performed throughout surgery. The central sulcus was identified by phase reversal of the somatosensory evoked potentials. The motor cortex was mappe d by direct high-frequency (500 Hz) monopolar anodal stimulation. In the patient herein reported, stimulation of the "anatomically" defined p rimary motor cortex induced no motor response, as expected. Motor response was elicited only by stimulation of the cortex anterior to the precentral g yrus. There was no postoperative deterioration of motor function. These obs ervations indicate that the precentral gyrus was functionally "useless". Th e motor region was relocated into more rostral areas in the supplementary m otor carter. This translocation of function in the presence of an AVM indic ates cerebral plasticity.