Intraoperative neurophysiology of the cerebellum: a tabula rasa

PURPOSE: Cerebellar mutism (CM) is a condition that occurs predominantly in children, after posterior fossa surgery (PFS). It is characterized by motor, speech, and behavioral disorders. Despite widespread use of intraoperative neurophysiological monitoring (IONM), little is known about the neurophysiological aspects involved in the pathophysiology of CM. We reviewed the IONM literature to identify working hypotheses aimed to investigate intraoperatively the circuits involved in CM. METHODS: A systematic review of the literature was conducted using PubMed central database. Papers describing the use of IONM techniques in the cerebellum were selected, thoroughly reviewed, and discussed. RESULTS AND DISCUSSION: Only two studies reported the use of intraoperative neurophysiology of the cerebellum, suggesting a possible somatotopic motor organization of the cerebellar cortex. In addition, extra-operative studies using transcranial magnetic stimulation showed the possibility to modulate-possibly through the dentato-thalamic-cortical (DTC) pathway-primary motor cortex output using an appropriate cerebellar stimulus. In theory, the preservation of this either inhibitory or facilitatory modulation may predict the preservation of this pathway, while a loss of the effect may indicate an injury to the pathway, and predict a CM. Analogously, in the extra-operative setting, the comparison of pre-operative and post-operative transcranial magnetic stimulation of the cerebellum may predict the onset of CM whenever a pre-existing modulatory effect is lost as a result of surgery. CONCLUSION: Virtually, no data exist on the intraoperative neurophysiology of the cerebellum. This limited knowledge, nevertheless, offers a unique opportunity to pediatric neurosurgeons to develop and test working hypotheses on the pathophysiology of CM, through the use of IONM.