Information alert

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For some patients having a craniotomy to treat a tumour, there is a risk of injury to the brain surface (cortex) or the underlying connecting wires (white matter) that control movement.

Movement is also called motor function. An injury to these areas of the brain during craniotomy can cause weakness, or even paralysis down one side of the body.

The risk of injury depends on how close the tumour is to the motor areas of the brain. If the risk to your motor function during your craniotomy is high, your surgeon might suggest a technique called motor mapping and monitoring. We can perform this under general anaesthesia.

Electrodes are placed on the head, limbs, and surface of the brain. The surgery is performed in the standard way but the electrodes are monitored to look for any break in the signal between the brain and the limbs that might suggest a potential injury.

A separate probe is used to stimulate parts of the tumour before they are removed to establish areas critical to motor function before and during removal of the tumour. This will guide the surgeon to stop the procedure if necessary or allow them to continue to take more of the tumour if it is safe.

Motor mapping and monitoring is not needed for every patient. It does have some complications. Your surgeon will be able to explain the risks and benefits to you in full but the main risks are as follows:

  • Having motor mapping and monitoring might increase the duration of an operation, meaning more time under anaesthesia. There is a very small chance that this could increase the risk of post-operative infection or complications of general anaesthesia, such as chest infection.
  • The use of electrical stimulation during motor mapping and monitoring can induce an epileptic seizure. This risk is around three per cent. If you have a seizure during the procedure, you may need to take medication to prevent further seizures. The surgeon may not be able to continue with motor mapping and monitoring following a seizure.
  • Motor mapping and monitoring can fail at any stage in the procedure should the machinery break down or wires become disconnected. This would be a very rare event. Should this happen your surgeon would make a judgement as to how far to continue with the tumour removal.

Even with the use of motor mapping and monitoring, there remains a risk of injury to motor function. Some patients having surgery to tumours in the motor area of the brain will have some temporary weakness. This can be quite intense. The use of motor mapping and monitoring can help us predict whether any weakness will be temporary but in a small number of patients, weakness will be long-term.

If it is felt that motor mapping and monitoring is not suitable for you, or you choose not to undergo this, we can perform a more limited operation to reduce the tumour size and provide tissue for diagnosis.

We may consider you for a procedure where you are awake, or for a biopsy.

If your surgeon is planning to use motor mapping and monitoring under general anaesthesia they will discuss this with you during as part of the consent process, and will be able to answer any of your questions.

If you need a large print, audio, braille, easy read or translated copy of this document, please contact the department directly. We will try our best to meet your needs.


Page last updated: 23 May 2024

Review due: 01 March 2025