Vestibular Schwannoma Surgery with the use of Intraoperative Monitoring

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1 Vestibular Schwannoma Surgery with the use of Intraoperative Monitoring Division of Neurosurgery, University of Cape Town August 2018 SNSA Sonia Nunes, Alan Taylor, David Le Feveure

2 Vestibular Schwannoma Surgery Vestibular schwannoma (VS) is a benign tumor that arises from one or more constituent nerves comprising the eighth cranial nerve complex Goals in Vestibular Schwannoma (VS) treatment: Complete removal in one stage Preservation of neurological function Preservation of patient s quality of life Benefits of IOM Localization of the nerve displaced by tumour distortion Detects nerve injury during dissection Provides a means for assessing nerve function after dissection is complete

3 40 patients underwent surgery for VS all had IOM 38 had no post operative deficits Rectosigmoid surgical procedure and microscope Anesthetic Regime- TIVA protocol UCT Neurosurgery Required optimal Responses NO movement NO NMJ/muscle block NO Hypotension Normal Temperature Drugs causing interference with IOM Ketamine Dexmedatomidine Muscle Relaxants, Volatile agents and centrally acting- Diazepam

4 Technique Peripheral line with 3 way tap with Propofol/ Remifentanil infusions transfer to CVP quick Induction of Midazolam, 2% Propofol, Initial Fentanyl Suxamethonium for intubation Insert bite blocks, Temperature probe Antibiotics Dextrose in patients with low HGT or potentially low HGT Tend to lower does Propofol, periods of increase, but total dose important Use Opiates Waking Introduce Volatile ASAP with standard dose Remifentanil usually after dural closure and post IOM closing baselines DR RICHARD COOKE

5 IOM Modalities MEPS CMEPS Free- Running EMG ABR (dependent on clinical picture) Mapping Corticobulbar MEPS (CMEPS) Specific to motor pathways of the cranial nerve Essential to differentiate from peripheral stimulation Value to surgical outcome if good signals are obtainable Requires skilled neurophysiologists for interpretation

6 CMEP Stimulation Techniques

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9 Mapping Facial Nerve The distance from the nerve and the amount of intervening tissue will determine the current setting needed to elicit nerve depolarization.

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11 Post Operative Evaluations Facial Nerve function was evaluated using House Brackmann (H.B) grade Categorized as excellent (H.B grade 1/2), intermediate (H.B grade 3/4), or poor (H.B grade 5/6).

12 Case Reports Case 1 53 year old female patient presented with left VS Symptoms: Left sided pins and needles on face, sharp facial pain Numbness Left side hearing loss Radiation Gamma Knife

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14 Opening Baselines :Motor Evoked Potentials (MEPS) opening baselines at 300 V were attained bilaterally for upper limbs and 600 V for lower limbs bilaterally. Corticobulbar Facial nerve MEPS were attained at 500 V on the left side at supramaximal thresholds.

15 CMEPS- Facial decreased by 50% from opening baselines. CMEP alarm was called, and complete tumor resection was not possible. Post operatively woke up with a HB of 2.

16 Neurotonic Discharges The burst potential, which consists of a single polyphasic response due to near simultaneous activation of multiple motor units.burst potentials are observed after direct contact of the nerve with surgical instrumentation and are fatigable with repeated nerve contact.

17 Facial Nerve discharges during tumor removal. Arrows illustrating Facial nerve channels

18 Case 2 58 year old male with right sided VS- 4cm Symptoms Off balance Dizziness Right sided hearing loss Right facial numbness

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20 Opening MEPS C1/2/1 5 ST 400V and CMEPS C4/Z 4 ST and 1 ST 200 V

21 Facial CNAP with Bipolar probe at 0.1mA. Free Running EMG with sporadic irritation post FACIAL nerve stimulation

22 Neruotonic Discharges- A Train

23 Closing CMEPS C3/Z ; C4/Z 4ST and 1 ST 200V

24 Closing Baselines MEPS C1/2/1 5ST 400V ALL MEPs present

25 Philip et al Journal of Neurosurgery

26 Conclusion