NS-01PEDIATRIC INTRAOPERATIVE NEUROPHYSIOLOGICAL MONITORING IN POSTERIOR FOSSA SURGERY

Intraoperative neurophysiological monitoring (IOM) has recently become a promising tool in neurosurgery. Experiences in children are scattered and the real contribution of this technique to extent of resection and post-operative neurological impairment prevention has not be fully determined yet. We describe our experience in 33 consecutive posterior fossa surgical procedures (30 patients, 19 males and 11 females) in the last two years. Standard monitoring setting included trans-cranial motor evoked potentials (tcMEP), somatosensory evoked potentials (SEP), continuous electromyography (EMG) and brainstem evoked potentials (BAEPs). Relevant IOM information was recorded and correlated to tumor characteristics, intraoperative modifications of surgical strategy, post-operative neurological deficits. Spontaneous EMG activations were observed in 100% of brainstem lesion, in 80% of those infiltrating the floor of the IV ventricle and in less than 50% of cerebellar hemispheric ones. Brainstem infiltration was found to be highly predictive for transient EMG activation (94% in infiltrating vs 37% in non-infiltrating lesions). Transient EMG activation was highly predictive of early post-operative neurological impairment (84% at 72 hours) but did not correlate with long term neurological deficits (35% at 3 months). MEP modifications were only found in presence of brainstem infiltration and resulted in modification of surgical strategy. 75% of patients showing potential drops were found to suffer early motor impairment after surgery. SEP modifications were also rare (12%) but correlated to early post-operative sensibility/motor deficit (75%). No significant variation of BAEPs was observed in our study. No specific IOM pattern was observed in the two patients with post-operative posterior fossa syndrome.