1. Intraoperative Electroencephalography (EEG): Aetna considers intraoperative scalp EEG medically necessary for the following indications:

   1. Monitoring cerebral function during carotid artery surgery; or
   2. Monitoring cerebral function during intracranial vascular surgical procedures.

   Aetna considers intraoperative EEG experimental and investigational for open-heart surgery and for all other indications because its clinical value has not been established.

   Note: The use of intraoperative EEG to monitor brain function for anesthetic drug administration in order to determine depth of anesthesia is considered integral to the anesthesia and not separately reimbursed. In addition, this use of intraoperative EEG is considered experimental and investigational.

2. Grid Monitoring (Electrocorticography, ECoG): Aetna considers grid monitoring to determine the location of the epileptogenic focus for possible surgical resection medically necessary for members with intractable seizures when any of the following conditions is met:

   1. Seizures arise from functionally important brain areas; or
   2. Surface (scalp) electroencephalogrphy (EEG) recording did not adequately localize the epileptogenic area, or
   3. There is a discordance between electrophysiological localization and that provided by other neurodiagnostic studies suggesting an abnormality in more than one region of the brain.

Aetna considers grid monitoring experimental and investigational for all other indications because its clinical value for these indications has not been established.

Notes: Grid monitoring is considered appropriate only when used by centers that have expertise and experience, especially with younger persons.

See also CPB 0322 - Electroencephalography (EEG) Video Monitoring, CPB 0394 - Epilepsy Surgery, and CPB 0425 - Ambulatory Electroencephalography.

For patients with intractable seizures, the best surgical outcome is attained after precise localization of the seizure focus. Scalp electroencephalography (EEG) monitoring may be insufficient and invasive subdural EEG monitoring (by means of subdural grid electrodes) has been used. Subdural electrodes provide coverage of large areas of neocortex and are ideally suited for evaluating children with intractable epilepsy and to functionally map critical cortex.

Multi-contact depth electrodes may be implanted into the brain to record electrical activity from deep or superficial cortical structure. Strips or rectangular grid arrays (subdural electrodes) can be placed under the dura to record activity in this region.

Subdural grid electrodes can be used for recording as well as for stimulating neural tissue to identify the underlying function (e.g., language areas, sensation or motor function). These electrodes remain in place for several days to up to 1 to 2 weeks, as needed to record seizures and map brain. They are then removed and epilepsy surgery performed, if findings are favorable for such surgery. In some patients in whom invasive monitoring fails to locate the seizure focus, re-investigation with invasive subdural electrodes can identify the origin of seizure and allow successful surgical treatment.

Invasive EEG monitoring with subdural grid electrodes is associated with significant complications; however, most of them are transient. Higher complication rates are related to an increased number of electrode contacts, increased length of the monitoring period, placement of burr holes in addition to the craniotomy, and multiple cable exit sites.

An American Academy of Neurology Technology Assessment (Nuwer, et al., 1990) stated that electrocorticography (ECog) from surgically exposed cortex can help to define the optimal limits of a surgical resection, identifying regions of greatest impairment. Regions of attenuated or absent EEG, or those with relatively increased slow activity, decrease in fast activity, or abnormal spike discharges help to define regions of cortex that are impaired or abnormal. When used together with long-term EEG/video monitoring, ECoG can help to define the limits of resection for surgery for epilepsy.

An American Academy of Neurology Technology Assessment (Nuwer, et al., 1990) stated that intraoperative scalp EEG monitoring has long been carried out in an effort to safeguard the brain during carotid endarterectomy. The assessment stated that this technique has been shown to be safe and efficacious for such use and for other similar situations in which cerebral blood flow is at high risk. For this purpose, monitoring should be carried out at least at the anterior and posterior regions over each hemisphere. The AAN technology assessment stated that sixteen channels are preferable to identify occasional embolic complications.

A Medicare National Coverage Determination (CMS, 2006) on EEG monitoring during surgical procedures involving the cerebral vasculature states that EEG monitoring may be covered routinely in carotid endarterectomies and in other neurological procedures where cerebral perfusion could be reduced. Such other procedures might include aneurysm surgery where hypotensive anesthesia is used or other cerebral vascular procedures where cerebral blood flow may be interrupted. A Medicare National Coverage Determination on EEG monitoring for open-heart surgery stated that the value of EEG monitoring during open heart surgery and in the immediate post-operative period is debatable because there are little published data based on well designed studies regarding its clinical effectiveness. The NCD states that the procedure is not frequently used for this indication and does not enjoy widespread acceptance of benefit.

One or two channel intraoperative EEG analysis modules have been used by anesthesiologists to gauge depth of anesthesia, such as the Bi-Spectral device (BIS). Such use of limited channel intraoperative EEG for monitoring depth of anesthesia (and level of consciousness) is considered integral to the anesthesia service and not separately reimbursable. In addition, a one or two channel EEG device does not meet the minimal technical requirements for EEG testing as set forth by the American Clinical Neurophysiology Society.