S119. Low threshold Linked Quadri-Polar (LQP)-TceMEP during left middle cerebral artery aneurysm clipping: A case report

Abstract

Introduction Traditional TceMEP stimultion (one anode and one cathode) during aneurysm surgery is limited due to the use of higher stimulation intensity ( ∼ 150 V) activating the motor tract at a subcortical level, bypassing the cortical and superficial subcortical level. (LQP)-TceMEP technique has the advantage of using two anodes and two cathodes stimulating electrodes bilaterally. Using lower threshold stimulation allows widening the range of current spread, and may activate a more cortical or superficial subcortical level. Methods A 65 year old female underwent an elective surgery for a left MCA bifurcation clipping. No history of neurological disease or contraindication for intraoperative neurophysiological monitoring (IONM). Image : 7 mm AP by 5 mm transverse by 6.5 mm cranio-caudal posteriorly projecting saccular aneurysm at the left middle cerebral artery (MCA) bifurcation. Baselines were obtained prior to incision, and Desfluorane:3.0%, Propofol:75 g/kg/min. Remifentanil 0.3 g/kg/min, was implemented for this case. We strongly recommend TIVA for this type of cases. SSEPs (MN-UN-PTN). (LQP)-TceMEP at low threshold (40–48 V), train of 4, ISI 1.5, PW:75. CMAP were recorded from distal muscles: brachioradialis or flexor carpi radialis, abductor pollicis brevis, first dorsal interosseous and abductor hallucis. EEG. Results After placement of the first temporary clip at the M1 position there were no (LQP)-TceMEP changes noted at 48 V/150 mA. After another temporary clip was placed at the aneurysm neck, the potentials remain stable at 48 V/152 mA. After placement of a longer clip at the base of the neck of the aneurysm, the (LQP)-TceMEP showed significant changes at 48 V/150 mA and the intensity was increased to 54 V/158 mA with no improvement noted; the surgical team was notified. The upper and lower extremities cortical component of the SSEPs remain unchanged related to aneurysm clipping.After approximately 20 min the (LQP)-TceMEP was able to be evoked, however at a higher stimulation intensity (60 V), which we hypothesized to be bypassing the area of injury. Conclusion The use of the (LQP)-TceMEP technique gave us the opportunity to monitor the motor pathway continuously without patient movement related to transcranial stimualtion and without interfering with the surgical procedure due to the low stimulation used in this case, (40–48 V). With low threshold stimulation, we assume activation of the motor tract at a cortical or superficial subcortical level without bypassing critical brain areas. (TIVA) strongly recommend (not in this case), we had reliable responses throughout the case (until the aforementioned incident), which was also dependent on the patient’s preexisting conditions and body type. After surgery, the patient demonstrated a pure motor deficit (right hemiplegia), expressive aphasia (Broca’s area) and normal sensation. Imaging studies showed cortical (left inferior frontal lobe) and subcortical stroke. Three months after surgery the patient recovered movement and speech.