Monitoring motor function during resection of tumours in the lower brain stem and fourth ventricle

OBJECTIVES: Even in the days of modern microsurgery, the removal of a brain stem lesion remains a surgical challenge. Especially when operating on children, the prognosis is directly related to the radicality of the resection; however, a radical resection is often associated with surgical morbidity. Intraoperative neuromonitoring could help to minimise the surgical morbidity, but few studies have been performed to clarify the value of this monitoring. We investigated a prospective series of 21 patients with lesions involving the brain stem for the prognostic value and benefits of neuromonitoring.

METHODS: We performed intraoperative neuromonitoring of cranial nerve function by electromyography (EMG) and motor evoked potential (MEP). The results were correlated with postoperative neurological deficits.

CONCLUSIONS: There is a good correlation between intraoperative neurophysiological events and postoperative neurological deficits in patients with lesions of the brain stem. In general, transient, prolonged, spontaneous activity in EMG is associated with a transient paresis of the respective muscle, whereas a permanent spontaneous activity is associated with a permanent deficit. Intraoperative neuromonitoring reliably predicts postoperative neurological function in patients with tumours of the lower brain stem and fourth ventricle. This neuromonitoring guides the neurosurgeon in the operation and may decrease surgical morbidity. We recommend using monitoring of MEP and EMG of the lower cranial nerves in surgery on all patients with lesions involving the lower brain stem and fourth ventricle.