Electrophysiology in Spinal Surgery

Intraoperational neuromonitoring in surgery of intradural tumors of spinal cord
Assoc.Prof.Selcuk GOCMEN, Neurosurgery Department, Anadolu Medical Center, In Affiliation with John Hopkins Medicine

Surgical strategy

• Preop. clinical status
• Location / tiny thoracic vascularity
• Radiological characteristics/spinal cord atrophy
• Plane between spinal cord & tumor
• Biopsy when infiltrative nature ?
• Long term control/cure with preserved function
• IONM (neuromonitoring)
• Microsurgery w/wo CUSA
• Intraoperative USG/Fluorescein filter microsope?

Surgical steps

• Radiological confirmation of level
• Opening – One level above & below incision – Laminectomy – Postlaminectomy kyphosis – Pay attention in pediatric group
• Laminoplasty
• Unilateral approach – Start from cranial side – Strict epidural hemostasis

Dural opening

• Slightly Trendelenburg position – Preventing over drainage of CSF
• Arachnoid knife / surgical blade (no 15/11)
• Hang up suture of dura & arachnoid
• Cottonoid patties & strips – Protection of medulla – No direct suction – Special suction cannula


• Dorsal median sulcus (DMS) – Midline – Shifting due to tumor!
• Sensory pathways disorders
• Dorsal root entry zone (DREZ) – Off the midline tumors – Asymetric neuro/pain – Between two roots – Motor pathway damage!
• Exophytic tumors


• Dorsal Median Sulcus – Not a sulcus – No arachnoid – No crossing axons – Thin blade of collagen from pia mater – Indicator; dorsal sulcal vein
• Avoid bipolar coagulation
• If necessary, discontinuous (holocord tumors)
• Pial stitching for medulla retraction

Microsurgical resection

• Micro instruments – Cranio-caudal
• Bipolar
• CUSA – In-out debulking – Motor pathway damage!
• Laser – CO2 / Nd:YAG – Shrinkage – IONM continues
• Microscope (fluorescein?)

Pial-Dural closure

• Goto et al. 2003 Neurosurg – Arachnoid - Dorsal tethering – Painful dysesthesia
• Raco et al. 2005 Neurosurg – 5% reoperation for dorsal tethering
• Dural closure only (5-6/0 vicril-prolene)

• 3% of CNS astrocytoma
• NF1 may associated
• Heteregeneous pathology – Low-grade, fibrillary/pilocytic (75%) – Malignant, glioblastoma/ganglioglioma/oligodendroglioma
• AA & GBM (10% peds & 20% adults)
• First three decades
• Cystic
• Diffuse cord enlargement, multiple levels, holocord
• More infiltrative - poor plane
• Heterogeneous enhancement
• Aggressive resection versus long term benefit questionable


• 3th intramedullary spinal tumor
• Non-encapsulated vascular origin
• Pial attachment / dorsal or dorsolat. location
• 1/4 of patients with VHL (cervical location) – Type I wo / Type II w pheochromocytoma
• 80% syptomatic by 4th decade
• Presentation similar to glial neoplasm – Rarely present sudden deficit from hemorrhage
• Bright homogeneous enhancement
• No more than 1 VB in length
• 80% cystic tumor nodule / syrinx
• Angiography & embolization possible prior to surgery
• 60% postop. exacerbation of signs


• 3% of CNS, 60% in spinal cord
• NF2 (gene merline) may associated
• Most of histologically benign – Cellular (C spine or anywhere)grade II-III – Myxopapillary (conus, slightly M)
• Mean age 40 y/o
• Homogeneous enhancement
• Cystic degeneration (>50%) – Not predictor for outcome after surgery
• Diffuse cord enlargement, multiple levels
• Myelotomy length according to tumor size
• Sharp delineation from cord, good plane
• Total resection is possible
Electrophysiology in Spinal Surgery
Learning Objectives
Electrophysiological monitoring of spinal cord and roots history
Requirement and Purpose
Monitoring techniques
Affecting factors
Reliable and safe threshold values
Threshold deviations and distortions history
Necessity of Neuromonitorization
Spinal cord tumors
Legal protection?!
Purpose of Neuromonitorization
Evaluation of spinal cord and nerve roots in risky surgeries
Avoiding neurological damage
Revision cases 40%
Pediatric cases 55%
Implantation cases 2 times high
Neurological deficit / neuromonitorization
Nerve root 11%
Cauda equina% 8
Spinal cord 40%
Neurological Deficit Recovery
No healing
Nerve root 4.7%
Cauda equina 9.6%
Spinal cord 10.6%
Partial recovery
Nerve root 46.8%
Cauda equina 45.2%
Spinal cord 43%
Full recovery
Nerve root 47.1%
Cauda equina 45.2%
Spinal cord 45.7%
Anesthesia technique

BIS: EEG value indicating the degree of alertness
Appropriate value range: 50-65
Non-invasive cutaneous system
Total iv anesthesia
No muscle relaxant (MEP affected)
Intraoperative Neurophysiological Monitoring
D wave
Multimodal Monitoring
Threshold value definition
First used for correction of scoliosis
Dorsal column-medial lemniscus pathway
Tactile discrimination
Vibration / proprioception
Primary somatosensory cortex recording
Not in real time!
No change in ischemic arterial ischemia!
Continuous monitoring
92% sensitivity - 98% specificity
Somatosensory evoked potentials
Median-ulnar & Posterior tibial-peroneal
Spinal Cord Functions
Nerve root function monitoring does not have a lot of value
Normal SSEP
N20 (Negative potential-upper extremities)
P37 (Positive potential-lower extremities)
Basal recording values
Before Anesthesia
50% reduction in cortical amplitudes
10% increase in cortical latency
Unilateral changes
Surgical maneuvers
Perfusion problems
Anesthesia cooperation and evaluation
Factors Affecting SSEP
Halogenated agents, nitrous oxide
Electrical interferences
Incorrect negative% 1-25
Transcranial motor evoked potentials (1990s)
Cortical neurogenic stimulation
Single pulse (very sensitive to anesthetic effects)
Multi-pulse stimulation
Peripheral nerve record
Corticospinal tract
Muscle recording (Compound muscle action potential-CMAP)
Spinal cord (D wave - epidural recording over T11)
Recording Muscles
Upper Extremity (C3-4)
APB (intrinsic)
Forearm flexor & extensor
Lower limb (C1-2 / 3-4)
they adductor
Plantar Foot Muscles
Threshold Value Interpretation
Always / No criteria
Most used road
Total loss of MEP signals
Amplitude criterion
Basal threshold value criterion
Criteria of wave morphology
Cannot perform continuous monitoring
Send frequent stimulus
D wave measurement is not possible in every case
Technical difficulties
95% of the upper extremity
65% of the lower extremity
40% if preop motor defect
Total i.v. anesthesia
DBS, Cochlear implant, Cardiac battery
Previous cranial surgery
sEMG (free-run)
No stimulation, spontaneous recording
Surgical manipulations
Nervous root pushing, pulling, compression
Thorn or explosion style waves
Cautery, ECG, motor use
* Pedicle screw and direct intradural fibril stimulation
Breaking the medial wall of the pedicle
Lumbar Threshold
<10 mA (+)
10-20 mA (-) 90% (CT control)
> 20 mA (-)
Thoracic threshold
<6mA (+)
* hydroxyapatite screws not suitable
Spinal Surgery
Sensitivity 52% & specificity 100%
Sensitivity 100% & specificity 96%
sEMG (root damage)
Sensitivity 30% & specificity 95%
Sensitivity 100% & specificity 25%
Potential Fall
Check electrodes
Increase MAP level
Check Hb-Htc
Warm the patient and the surgical pitch
Look at the depth of anesthesia
Stop surgery, check for pressure-damage
Remove press-straighten
Remove deformity correction rod
Remove screws
42 Y / K
Significant paraparesis on the left for 1 year
Abnormal achilles clonus on the left
Babinski bilat. positive
DTR hyperactive
T7est8 hypoesthesia
Unable to get KCR
T9 intradural extramedullary tumor
Neuromonitor Records
Significant tibial response on the left, prolongation of latencies and amplitudes
Prone position
IV anesthesia
Right unilateral approach
T9 hemi / T8-10 partial laminectomy
Microsurgical resection
Perop falling on the right tibial responses
Initial values
Perop values
Multimodal Neuromonitorization
Basal value recording
MEP before or after risky maneuvers
D wave measurement in case of doubt
Compliance with anesthesia
Neurology specialist control
Legal protection in risky surgeries?!
Thank you