S115. Multimodal intraoperative neurophysiology monitoring during the resection of a 4th ventricular mass in a 2 year-old boy with hemifacial spasm and seizure

Abstract

Hemifacial spasm is a disorder of the seventh cranial nerve characterised by irregular, involuntary, clonic or tonic spasms of the facial muscles. In adults it is typically a primary disorder, predominantly affecting females in the fourth and fifth decades. Neonatal onset is much rarer, in and in most instances associated with a posterior fossa mass. We report the case of a 2 year-old boy who, soon after a normal and term delivery, developed unilateral hemifacial twitching. An associated ipsilateral mass in the floor of the fourth ventricle was subsequently seen on magnetic resonance imaging of the brain. A craniotomy was performed for resection of the visualised mass. A complex post anaesthetic Neurophysiology set up for intraoperative neurophysiology monitoring (IONM) and mapping was required. Brainstem auditory evoked potentials (BAEP), trans-cranial electrical motor evoked potentials (tceMEP) from face and upper limb, somatosensory evoked potentials (SEP) from the upper limbs, cranial nerve mapping and electrocorticography (ECOG) were all performed. Subdermal needle electrodes were used to record from orbicularis oris, oculi, masseter, lateral rectus and abductor pollicus brevis muscles bilaterally for tcMEPs and cranial nerve monitoring. A monopolar stimulator with needle reference was used to stimulate the cranial nerves. Buds placed in the auditory canals were used for BAEP stimulation and held in with bone wax. After opening and exposure, an 8-contact depth electrode was placed into the lesion to record resting ECOG in a referential montage, checking for interictal epileptiform activity. SEPs were obtained from stimulation of the ulnar nerves in both upper limbs and recording from corkscrew electrodes on the scalp. Cranial nerve mapping allowed the surgical team to avoid damaging the intact structures. ECOG provided real-time interictal data directly from the lesion, with no intralesional epileptiform abnormalities recorded. At closure there were no significant changes from baseline SEPs and tceMEPs. The lesion was fully resected, and the patient had a post-operative neurological exam with no deficits noted as predicted by closing neurophysiology data. To date, the patient has had no further episodes. IONM played a pivotal role during this procedure for the surgical team to tailor their surgical approach safely with maximal resection.