“Unlocking the Potential of Brainstem Mapping and Reflex Monitoring in Pontine Tumor Resection”

We report a 54-year-old female who presented with an unsteady gait and a recent fall. MRI revealed a right Pons mass, suspected as a breast cancer metastatic disease. A craniotomy for a surgical biopsy was planned. The tumor was of few millimeters in diameter but relatively close to the Facial nuclei, Trigeminal sensory nuclei, and lemniscus pathways. Multimodal intraoperative monitoring (IOM) was used to avoid devastating intra-axial brainstem tumor surgical complications. Methods of choice for neurophysiological monitoring included: early brainstem auditory evoked potentials, free-running electromyography, cranial nerve mapping with direct nerve stimulation, Corticobulbar Motor Evoked Potentials (CoMEP): Oculi, Masseter, Nasalis, Oris, Glossopharyngeal, vocal muscles. Four extremities, Somatosensory, and Motor evoked potentials, and brainstem reflexes such as Blink, Masseter, and Laryngeal adductor reflex were also set up. Following mapping the fourth ventricle and identifying facial colliculi, the Surgeon made an incision to the presumptive tumor location. During the approach, Blink reflex monitoring was continuously done to avoid any impending damage to the Facial nucleus, Trigeminal principal nucleus, or their intra-axial connection. Dissection and adequate biopsy material acquisition was completed without IOM changes. The patient presented nausea and vomiting post-operative period in ICU. In this case, our primary focus was mapping the fourth ventricle to access the tegmentum and the Blink reflex for a true continuous IOM. Brainstem mapping enabled the Surgeon to make a safe entry for biopsy; Blink reflex Monitoring enabled to execute the biopsy without damaging nearby structures: Facial Nuclei, trigeminal sensory nuclei, and their interconnections located within the brainstem.