Bilateral epidural D-wave monitoring during resection of an eccentric cervical astrocytoma with evidence of asymmetrical corticospinal desynchronization.

BACKGROUND AND IMPORTANCE: The surgical management of intramedullary spinal cord tumours (IMSCT) poses inherent risk to neurologic function. Direct-wave (D-wave) monitoring is routinely reported to be a robust prognostic measure of spinal cord function via midline recording within the epidural or intradural space in a cranial-caudal montage. We explored the feasibility of bilateral epidural D-wave monitoring with routine evoked potentials in promoting safe and maximal resection in a patient with diminished midline D-wave baselines associated with an eccentric intramedullary cervical astrocytoma. CLINICAL PRESENTATION: We describe the presentation, surgical management, electrophysiological findings and post-operative outcome of a 46 year-old female patient who underwent two resections for an eccentric intramedullary cervical astrocytoma. During the first procedure we encountered clinically significant motor evoked potential signal change and discontinuation of resection pending further review. Midline D-wave signals showed no change, however peak amplitude was diminutive (7 uV) and overall morphology was characteristic of corticospinal desynchronization. Post-operatively the patient experienced significant but transient left sided weakness. A subsequent revision procedure incorporating ipsilesional and contralesional D-wave monitoring in addition to routinely incorporated evoked potentials was proposed in order to facilitate a safer resection. The ipsilesional D-wave response was considerably lower in amplitude (2.5 uV) in contrast to the contralesional D-wave (20 uV). CONCLUSION: To the authors' knowledge this is the first description of bilateral D-wave monitoring as an adjunct to cranial-caudal D-wave montages during IMSCT surgery. In patients with corticospinal desynchronization evidenced by abnormal midline D-wave morphology, bilateral D-wave monitoring in conjunction with routine evoked potentials may be clinically indicated for preservation of motor function and promotion of safe and maximal resection.

Facilitating complete resection of intrinsic motor cortex glioma with titration of high-frequency cortico-subcortical mapping train count informed by navigated transcranial magnetic stimulation: illustrative case.

BACKGROUND: The dilemma of neuro-oncological surgery involving suspected eloquent cortex is to maximize the extent of resection while minimizing neurological morbidity, referred to as the "onco-functional balance." Diffuse lower-grade gliomas are capable of infiltrating or displacing neural function within cortical regions and subcortical white matter tracts, which can render classical anatomic associations of eloquent function misleading. OBSERVATIONS: This study employed presurgical navigated transcranial magnetic stimulation (nTMS) to determine the motor eloquence of a diffuse lower-grade glioma at the superior frontal gyrus extending and intrinsic to the primary motor cortex in a 45-year-old female. Positive nTMS findings were confirmed intraoperatively with high-frequency direct cortico-subcortical stimulation (HF-DCS). Modification of the HF-DCS train count from train-of-five to train-of-two permitted resection beyond classic anatomical boundaries and conventional HF-DCS safe stopping criteria. LESSONS: Anatomical correlates of function can inaccurately inform the surgical management of diffuse lower-grade glioma, which represents the utmost opportunity for progression-free survival. Integrating an individually tailored nTMS-DCS surgical strategy contributed to complete resection, negating the requirement for adjuvant therapy. Serial nTMS follow-up may assist with the characterization of tumor-induced functional reorganization. https://thejns.org/doi/10.3171/CASE24197.