Intraoperative neurophysiological monitoring during resection of infratentorial lesions: the surgeon's view

Abstract

OBJECTIVE Methods of choice for neurophysiological intraoperative monitoring (IOM) within the infratentorial compartment mostly include early brainstem auditory evoked potentials, free-running electromyography, and direct cranial nerve (CN) stimulation. Long-tract monitoring with somatosensory evoked potentials (SEPs) and motor evoked potentials (MEPs) is rarely used. This study investigated the incidence of IOM alterations during posterior fossa surgery stratified for lesion location. METHODS Standardized CN and SEP/MEP IOM was performed in 305 patients being treated for various posterior fossa pathologies. The IOM data were correlated with lesion locations and histopathological types as well as other possible confounding factors. RESULTS Alterations in IOM were observed in 158 of 305 cases (51.8%) (CN IOM alterations in 130 of 305 [42.6%], SEP/MEP IOM alterations in 43 of 305 [14.0%]). In 15 cases (4.9%), simultaneous changes in long tracts and CNs were observed. The IOM alterations were followed by neurological sequelae in 98 of 305 cases (32.1%); 62% of IOM alterations resulted in neurological deficits. Sensitivity and specificity for detection of CN deficits were 98% and 77%, respectively, and 95% and 85%, respectively, for long-tract deficits. Regarding location, brainstem and petroclival lesions were closely associated with concurrent CN IOM and SEP/MEP alterations. CONCLUSIONS The incidence of IOM alterations during surgery in the posterior fossa varied widely between different lesion locations and histopathological types. This analysis provides crucial information on the necessity of IOM in different surgical settings. Because MEP/SEP and CN IOM alterations were commonly observed during posterior fossa surgery, the authors recommend the simultaneous use of both modalities based on lesion location.

ICAR: endoscopic skull‐base surgery

“…Thus, interventions addressed to reverse the significant SSEP changes by increasing perfusion, modifying or pausing the surgical procedure, might prevent neuronal death or infarction in some cases. Resection of tumors in petroclival and brainstem regions and vascular tumors such as cavernomas and hemangioblastomas are most likely to result in SSEP changes due to nerve traction and vascular injury, respectively . ICA injury is an uncommon and underreported complication of ESBS surgery.…”

“…The significant challenge in CMAP response for CNs is lack of normative data for the onset latency and amplitude during the ESBS or conventional skull‐base approach to determine significant changes. Based on published reports on conventional skull‐base surgery and University of Pittsburgh experience during ESBS (unpublished data, University of Pittsburgh, Thirumala P, Gardner P, Wang E, Snyderman C), monitoring extraocular CNs is particularly useful in surgeries of the clivus, cavernous sinus, pons, and midbrain; trigeminal nerve in surgeries involving Meckel's cave and the infratemporal fossa; and facial nerve and lower CNs in surgeries involving the petroclival region …”

“…In large tumors that encompass CNs completely, corticobulbar MEP maybe more helpful than tEMG during initial tumor debulking because it can provide information about the integrity of the CNs before obtaining tEMG response via direct stimulation. Although not performed widely, corticospinal MEP has the potential to serve as a useful adjunct in monitoring corticospinal changes during petroclival tumor resection …”

Intraoperative Neurophysiological Monitoring for Endoscopic Endonasal Approaches to the Skull Base: A Technical Guide

“…Transcranial electrical motor evoked potentials (tceMEPs) have played a role in the operating room since it was first demonstrated that the pulse-train stimulation technique could successfully evoke MEPs in the anesthetized patient [ 31 , 55 ]. While routine use of tceMEP monitoring began in spinal surgery in the 1980s, it is now also commonly used in many supratentorial [ 56 – 61 ] and infratentorial [ 62 – 66 ] procedures, as well as procedures in which peripheral nerves or spinal nerve roots are at risk [ 67 – 69 ]. Given the limitations of EEG and SSEPs mentioned above, the addition of tceMEPs to the multimodality IONM plan can paint a more comprehensive picture of nervous system function when monitoring cases using the EEA.…”

“…Inclusion of tceMEPs monitoring is the only means of detecting insult to the long-tract motor pathways. Although the utility of tceMEPs in detecting functional motor change has been demonstrated in a wide range of intracranial procedures [ 56 – 66 ], their efficacy using the EEA is scarce.…”