gms | German Medical Science

Microsurgical removal of brain stem lesions remains a surgical challenge: Anatomical landmarks are inconstant, especially in the immediate vicinity of the fourth ventricle. Moreover, subependymal location of caudal cranial nerve nuclei and displacement of the anatomy by the lesion add to the difficulty of complete resections with preserved function. However, especially when operating on children, the prognosis is directly related to the radicality of the resection. Intraoperative neuromonitoring might be helpful in minimizing surgical morbidity, so that we prospectively investigated a series of 21 patients with lesions involving the lower brain stem.

This prospective study included 21 patients with various lesions extending into the fourth ventricle. Neurological exams were performed preoperatively, postoperatively and on follow-up visits to assess surgical morbidity. Nervous structures were monitored intraoperatively by EMG and MEP. EMG activity was made audible to the surgeon and additionally reported. Neurophysiological changes and reactions of the surgeon (pausing and/or changing the site of manipulation) were documented. The intraoperative neuromonitoring results were correlated with postoperative neurological deficits and the numbers of true or false positive or negative monitoring events were recorded.

There was a good correlation between monitored intraoperative events and postoperative neurological function. The percentage of false positive or negative events was low (12% and 1,6% respectively). Transient or permanent pathological activity during intraoperative neuromonitoring was highly correlated with an attributable postoperative deficit. In general, transient prolonged spontaneous activity in EMG recordings was associated with transient paresis of the respective muscle, whereas permanent spontaneous activity was associated with a permanent deficit.

Intraoperative neuromonitoring may be used to predict postoperative neurological function in patients with tumours of the lower brain stem and fourth ventricle. In this study, intraoperative monitoring of motor function proved to be a valuable tool for guiding the neurosurgeon during the operation and might thus be helpful in reducing surgical morbidity.