Henry and Igor operating on Marian.
A craniotomy is a surgical procedure in which a section of the skull is removed to expose the brain underneath. It may be performed during surgery for various neurological problems, including epilepsy, or when an injury or infection has occurred in the brain. The sections of the skull that are removed vary in size, ranging from very small dime-sized pieces that are taken out in order to remove small tumors or drain blood clots to larger sections, called bone flaps, that are taken out to allow doctors to access the brain itself. A craniotomy is usually preceded by an MRI scan, and the surgeon uses the resulting image to determine where and how much bone will be removed in order best to access the relevant area of the brain.
When a patient has a tumor that is located near the region of the brain that controls motor and speech, a neurosurgeon may choose to perform the procedure while the patient is alert. A functional MRI (fMRI) can show areas of the brain that are activated during speech and motion, but the most accurate results are achieved by mapping these critical areas of the brain during surgery while the patient is awake. First, the patient is placed under anesthesia, and then doctors open his or her skull, carefully moving the skin and bone aside in order to gain access to the brain. Next, the patient is gently awakened. Because the brain itself does not have pain receptors, the patient usually does not experience discomfort during the procedure. A doctor -- often a neuropsychologist -- engages the patient in constant conversation or asks the patient to read while a probe with a mild electrical current is applied to the surface of the exposed brain. If the stimulation hinders the patient's performance of the task or causes the patient confusion, the area of the brain being stimulated is noted and that area is preserved.
Watch a video excerpt from Your Life in Their Hands, in which Henry Marsh performs an awake craniotomy.
The operating team then has a limited amount of time, usually no more than two hours from the moment the skull is opened, during which to remove as much of the tumor as possible. The patient continues to talk and engage with doctors as the operation is performed. This process lessens the risk of cutting into the fibers that connect speech areas. When as much of the tumor as possible has been taken out, the patient is put back to sleep. The skull is then closed and the procedure completed.
Source:
»Mayfield Clinic, Craniotomy
»UCLA Neurosurgery: Treatment Options: Awake Craniotomy
»BBC News: "I Was Awake During Brain Surgery"