Intraoperative Electrophysiologic Studies on the Functions of Nerve Roots Involved in Cervical Dumbbell-shaped Schwannoma and Their Clinical Utility

BACKGROUND: It is difficult to expect the degree of neurologic deficits after resection of involved nerve roots before and during the surgery for cervical dumbbell-shaped schwannoma. We present the results of studies for cervical nerve root functions in patients with cervical schwannoma using intraoperative electrophysiologic assessment and the potential of their clinical relevance is also discussed. OBJECTIVE: To present the utility of intraoperative electrophysiologic studies to detect the functions of the nerve roots involved in cervical schwannoma and adjacent nerve roots. METHODS: Five patients with dumbbell-shaped cervical schwannoma arising from the cervical nerve roots composing the brachial plexus were studied. Compound muscle action potentials (CMAPs) after stimulation of nerve roots involved in the schwannoma were recorded from upper limb muscles anatomically correspond to their myotome. Adjacent nerve roots were also stimulated. Motor-evoked potentials (MEPs) after transcranial electric stimulation were also recorded during surgery. In 3 patients, sensory nerve action potentials (SNAPs) after digital nerve stimulation were also recorded from cervical nerve roots. RESULTS: In 4 patients, CMAPs after stimulation of cervical nerve roots involved with the schwannoma were not obtained or were very small compared with those obtained after stimulation of adjacent nerve roots. In 2 of 4 patients, SNAPs after digital nerve stimulation were recorded with small amplitude from the nerve roots involved in schwannoma. Minimal (n=2, within 80% attenuation of amplitude) or no changes (n=2) were observed after total resection of the schwannoma and no apparent motor weakness occurred in these 4 patients. In a patient with cervical schwannoma involved in C8 nerve root, CMAPs with large amplitude were recorded after stimulation of the C8 nerve root. SNAPs after stimulation of digit V were recorded with larger amplitude from the T1 root compared with those recorded from the C8 nerve root. Intradural parts of the tumor arising from C8 posterior rootlets were completely removed after transaction of posterior rootlets. During removal of intraforaminal parts of the tumor, motor evoked potentials were decreased over 50% of controls. Incomplete removal was chosen to avoid deterioration of motor function. Transient dysesthesia of digit V and slight weakness occurred after surgery. CONCLUSIONS: The residual function of motor and sensory nerve roots involved with cervical schwannoma differed between individuals and could be detected using intraoperative electrophysiologic assessment.