This is a highly specialised procedure performed when tumours are present very close to areas of the brain that control movement, speech and language, to minimise injury to these areas and preserve function. An important part of the brain, which controls voluntary movement of the opposite side of the arm, leg, face and tongue, is called the motor cortex. (See fig below)
The anatomical region of the brain known as Area 4 (coloured red in the figure above) was given the name primary motor cortex after the Canadian Neurosurgeon Dr Wilder Penfield showed that focal stimulations in this region elicited highly localized muscle contractions at various locations in the body. The motor cortex also includes Area 6, which lies in front of Area 4 and is divided into the premotor area (or premotor cortex) and the supplementary motor area. The premotor cortex is believed to help regulate posture by dictating an optimal position to the motor cortex for any given movement. The supplementary motor area, for its part, seems to influence the planning and initiation of movements on the basis of past experience. The mere anticipation of a movement triggers neural transmissions in the supplementary motor area. Tumours in the Premotor and supplementary motor areas can be removed in most instances without any significant loss of function to the patient, though there may be some temporary weakness on the opposite side of the body if these areas are removed on the dominant side (i.e. in the majority of people (both right and left handed) the left half of the brain is dominant). However tumours in the primary motor cortex are difficult to remove without loss of function of the opposite side of the body. Any injury to the primary motor cortex is in most instances likely to lead to irreversible loss of function of the arm, hand , leg or face of the other side of the body.
If a glioma is present very close to the primary motor cortex then an 'Awake craniotomy' can be performed to minimise injury to this area. In this procedure the patient is awake (but pain free) during parts of the operation to remove the tumour. The surgeon and his team are able to talk to the patient while the operation is in progress. The surgeon stimulates various areas of the brain and looks for muscle contractions in the patient and sometimes correlates with electrical recordings obtained from specific muscle groups in the arm and leg. The patient is also asked to move the arm, hand, and leg repeatedly to observe for any decrease or loss of function while removal of the tumour is underway. In this way the surgeon is able to obtain a map of the opposite side of the body on the brain surface and is able to avoid injury to areas of the brain that he/she knows is responsible for movement. This is known as 'Cortical mapping'. This procedure is also performed when tumours that are very close to the speech / language areas of the brain have to be removed. In this case the patient is asked to repeat a variety of small simple tests (like naming objects, counting numbers etc) while the operation is underway to help prevent any injury to the speech & language areas of the brain. The risk of developing a neurological disability like weakness of arm / leg or difficulty in speech can be significantly reduced by performing this procedure where appropriate, but the risk can never be completely eliminated.
Carefully selected patients with a suspected malignant glioma on an MRI scan may be eligible for application of Gliadel wafers in the tumour cavity at the time of surgery to resect the tumour. A team of experts at the Multi disciplinary meeting will make the decision about the suitability for this treatment. If the patient is assessed and found suitable for this treatment then the Neurosurgeon will discuss this in detail with the patient and family at the initial consultation. Gliadel is a form of topical chemotherapy containing the drug called Carmustine (or BCNU), which has shown some benefit in clinical trials. NICE has approved this treatment in selected cases of newly diagnosed malignant glioma.