ORIGINAL ARTICLES   

Journal of Neurosurgical Sciences 2003 June;47(2):79-88

Copyright © 2004 EDIZIONI MINERVA MEDICA

language: English

Brain surgery in motor areas: the invaluable assistance of intraoperative neurophysiological monitoring

Sala F., Lanteri P.

Department of Neurosurgery, University Hospital, Verona, Italy

Aim. Surgery for ­tumors in the cen­tral and pre­cen­tral ­region, as ­much as for insu­lar ­tumors, plac­es at ­risk the func­tion­al integ­rity of the ­motor cor­tex and the sub­cor­ti­cal ­motor path­ways. These pro­ced­ures may there­fore ben­e­fit ­from the assis­tance of intra­op­er­a­tive neu­ro­phys­io­log­i­cal mon­i­tor­ing (INM). INM con­sists of “map­ping” and ­true “mon­i­tor­ing” (the con­tin­u­ous “on-­line” assess­ment of the func­tion­al integ­rity of neu­ral path­ways) tech­niques. In ­spite of the ­large inter­est in map­ping tech­niques, mon­i­tor­ing tech­niques ­have ­received ­less atten­tion. We ­describe our expe­ri­ence ­with intra­op­er­a­tive neu­ro­phys­io­log­i­cal map­ping and mon­i­tor­ing of ­motor ­tracts dur­ing sur­gery for ­brain gli­o­mas in or ­near ­motor are­as, in ­order to sup­port the fea­sibil­ity and reli­abil­ity of mon­i­tor­ing as an essen­tial ­adjunct to map­ping dur­ing sur­gery in ­these are­as.
Methods. Between September 2000 and January 2002, 51 ­patients ­were sur­gi­cal­ly treat­ed for ­brain gli­o­mas locat­ed in the pre­cen­tral gyr­us (45.1%), the post­cen­tral gyr­us (23.5%), ante­ri­or to the pre­cen­tral gyr­us (15.6%), or in the insu­la (15.6%). INM of the ­motor ­system con­sist­ed of mon­i­tor­ing mus­cle ­motor ­evoked poten­tials (mMEPs) record­ed via nee­dle elec­trodes insert­ed ­into the con­tro­lat­er­al ­upper and low­er extrem­ity mus­cles and elic­it­ed by trans­cra­ni­al mul­ti­pulse electri­cal stim­u­la­tion (TES). Once the ­dura was ­open and the cen­tral sul­cus was iden­ti­fied ­using the ­phase rever­sal tech­nique, mMEPs ­were elic­it­ed by ­direct stim­u­la­tion of the ­motor cor­tex (DCS). Motor map­ping was per­formed ­with a mono­po­lar elec­trode ­using the ­same stim­u­la­tion param­e­ters as ­used for mon­i­tor­ing ­except for ­much low­er inten­sity (up to 20 mA).
Results. Ninety-­eight per­cent of the ­patients exhib­it­ed record­able base­line mMEPs. The suc­cess ­rate of the ­phase rever­sal tech­nique was 95.8%. Eight ­patients pre­sent­ed dis­ap­pear­ance of mMEPs dur­ing ­tumor remov­al. Using cor­rec­tive meas­ures, all intra­op­er­a­tive chang­es in mMEPs ­were ­reversed in ­time to pre­vent an irre­ver­sible com­plete inju­ry to the ­motor ­system and no ­patient ­lost mMEPs at the end of the oper­a­tion. At dis­charge, 66% of the ­patients ­remained at ­their pre­op­er­a­tive stat­us, 4% ­improved, and 24% had a ­mild wors­en­ing as com­pared to the pre­op­er­a­tive stat­us ­assessed ­using the Medical Research Council ­scale; 6% of the ­patients pre­sent­ed a mod­er­ate to ­severe sup­ple­men­tary ­motor ­area syn­drome.
Conclusion. Monitoring tech­niques sig­nif­i­cant­ly imple­ment the reli­abil­ity and effec­tive­ness of INM ­since ­these pro­vide: 1) con­tin­u­ous “on-­line” assess­ment of the func­tion­al integ­rity of ­motor path­ways ­with high­er ­chance to ear­ly ­detect a pro­gres­sive mechan­i­cal or vas­cu­lar inju­ry to the neu­ral tis­sue, as com­pared to map­ping tech­niques; 2) low­er ­risk to ­induce intra­op­er­a­tive sei­zures and ­strong mus­cu­lar twitch­es as com­pared to the sin­gle ­pulse map­ping tech­nique; 3) pos­sibil­ity to mon­i­tor ­motor path­ways – ­using TES –­also ­when ­there is no ­direct ­access to the ­motor cor­tex.