Neurophysiology Department - Brain mapping and monitoring during surgery leaflet

Your surgeon would like you to have neurophysiology spinal cord monitoring during your surgery. This involves monitoring of the motor and sensory parts of your spinal cord that are at risk of injury either directly from surgery or indirectly from blood loss or stroke. The motor part is responsible for moving your arms and legs and is monitored using transcranial motor evoked potentials (MEPs), the sensory part is responsible for your sensation in your arms and legs and is monitored using somatosensory evoked potentials (SSEPs).

What are Transcranial Motor Evoked Potentials (MEPs)?

MEPs are responses recorded from your muscles when your brain is stimulated through your scalp. Once you are asleep and ready for surgery needle electrodes are placed in different muscles in your hand, leg and foot and corkscrew electrodes are inserted into your scalp for stimulation.

What is MEP monitoring?

During surgery your brain is stimulated through special corkscrew electrodes placed in your scalp, responses are recorded from the needle electrodes placed in muscles in your hand, leg and foot. The size of the responses obtained are monitored and significant changes reported directly to the surgeon. Changes in MEPs are used to predict the risk of weakness after surgery and if it is likely to be permanent or temporary. Feedback to the surgeon helps to protect you from permanent motor injury, weakness or paralysis. This aspect of monitoring is particularly important during spinal cord correction when the spine is manipulated by the surgeon.

After surgery

You may have small sore areas where the needle electrodes have been placed in your muscles and scalp. All electrodes are removed before you wake up.

Are there any risks to Transcranial MEPs?

Neurophysiological monitoring is considered safe; the most serious safety concern is seizure this is considered rare using the stimulus techniques required for transcranial MEP monitoring. No reports of seizures resulting from MEP monitoring in anesthetized patients have been published to date. There are unpublished observations by Deletis and MacDonald of rare seizure occurrences.

The placement of needle electrodes in a sterile manor for stimulation and recording have never been associated with inflammation or severe bleeding or more serious complications. The greatest risk associated with transcranial MEP monitoring is tongue biting, the incidence and severity of this is variable we estimate in approximately 10% cases there will be a tongue bite with variable severity.

Are there any alternative monitoring techniques?

The alternative technique to MEP monitoring is to perform the surgery with SSEPs only however SSEP monitoring only monitors the posterior portion of the spinal cord (no motor pathways) greatest risk of damage occurs in the anterior portion of the spinal cord therefore without MEP monitoring the risk of permanent motor injury, weakness or paralysis is significantly increased.

What if I don’t have MEP monitoring?

Without MEP monitoring you are at significant risk of permanent motor injury, weakness or paralysis which can only be assessed once you have been woken up at this point the damage may be irreversible. The risk is greatest during spinal cord correction.

What are Somatosensory Evoked Potentials (SSEPs)?

SSEPs are responses that are recorded from the brain when nerves in your hands or feet are stimulated. Corkscrew electrodes are placed in your scalp while you are asleep and stimulating electrodes placed at the wrist and ankle.

What is SSEP monitoring?

During spinal surgery the nerves in the hand or foot are stimulated and responses recorded directly from the brain. The responses recorded are monitored, changes in SSEPs are used to predict the risk of sensory loss after surgery. Feedback to the surgeon helps to protect you from permanent sensory loss which includes paraesthesia , numbness or complete loss of sensation.

After surgery

You may have small sore areas where the corkscrew electrodes have been placed in your scalp. All electrodes are removed before you wake up.

Are there any risks to SSEPs?

SSEPs are considered safe with no reported risks or side effects from SSEPs.

Are there any alternative mapping techniques?

Functional MRI mapping can be undertaken prior to surgery and used to guide surgery, this is not a live image and cannot be used for surgical monitoring.

What if I don’t have SSEP monitoring?

The surgeon won’t be able to monitor the posterior part of the spinal cord where the sensory pathways are located increasing the risk of a permanent sensory injury after surgery.

What type of spinal surgery requires MEP / SSEP / monitoring?

• Scoliosis surgery
• Spinal deformity / correction surgery
• Removal of spinal disc

If you have any questions (before or after your surgery) please ring 0151 529 5602