Intraoperative Neurophysiological monitoring, also called IONM, plays an important role in awake-asleep craniotomy, decreasing patient risk and improving patient confidence in the procedure.
What is a Craniotomy?
A craniotomy is a surgery that involves temporarily removing a section of the skull to gain access to the brain. Following the surgery, the piece of bone that was removed (called a bone flap) is replaced. Craniotomies may be recommended for:
- the diagnosis, removal, or treatment of brain tumors
- repairing a fracture in the skull
- repairing damage to the dura mater (lining of the brain)
- implanting devices designed to treat certain disorders like Parkinson’s
- Aneurysm repair
- Treatment of epilepsy
- removing arteriovenous malformations (AVM)
- Removal of blood clots or blood
- Relieving pressure following stroke or trauma
- draining an abscess in the brain
In some cases, the scalp incision is very small, as is the corresponding bone flap. In other cases that require a large bone flap, the skin incision is also bigger. The size of the incision depends on the cause for surgery. Craniotomies are only recommended when the physician believes the benefits outweigh the risks.
Understanding Awake-Asleep Craniotomy
During an awake-asleep craniotomy, the patient is conscious while the surgeon stimulates different parts of the brain and asks the patient to perform tasks that may be affected. By doing this step first, the surgeon is able to map out eloquent areas of the brain, that is, areas that affect speech and language. Because these parts of the brain cannot be clearly identified through MRI or other diagnostic testing, the awake portion of an awake-asleep craniotomy is important in decreasing the risk of poor patient outcome and neurological deficits.During an awake-asleep craniotomy, the patient is sleeping while the bone flap is removed, awake and conscious for mapping, and then asleep for the surgical procedure and the replacement of the bone flap. This is accomplished through careful administration of general anesthesia by a qualified anesthetist.
The Role of IONM
Intraoperative neurophysiological monitoring provides the surgeons with instant and very reliable feedback on the functioning of the nervous system during the times of the operation that the patient is asleep and cannot be evaluated clinically. It is also essential during the awake portions of this procedure, in helping the surgeon identify the eloquent areas of the brain mentioned above.Measurements are taken through sensors connected to the patient and monitored on site by an experienced neurodiagnostic technologist. A remote reading physician also monitors the activity. IONM ecompasses somatosensory evoked potentials (SSEP), transcranial motor evoked potentials (TcMEP), electromyography (EMG), electroencephalography (EEG), and brainstem auditory evoked responses (BAER).When IONM is used during neurological procedures, live monitoring aids in detecting deficits in neurological function. Should a deficit be detected, instant feedback ensures that surgeons are able to intervene immediately, instead of waiting for a wake-up test to be performed and then taking corrective action. This reduces patient risk and improves the chances of a positive outcome.
All surgeries are accompanied by inherent risk, but neurological surgeries such as craniotomies can pose higher risk than others. IONM provides instant feedback of neurological deficits during surgery to allow the surgeon to map the eloquent brain without waking the patient. Patients should consider selecting a surgeon who uses this state-of-the-art technology for their safety and best possible outcome.