Grid Monitoring and Intraoperative Electroencephalography

Number: 0289

Table Of Contents

Applicable CPT / HCPCS / ICD-10 Codes


Scope of Policy

This Clinical Policy Bulletin addresses grid monitoring and intraoperative electroencephalography.

  1. Medical Necessity

    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; or
      3. Monitoring cerebral function during parietal tumor resection or resection of lesion near the eloquent cortex.

      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, investigational, or unproven.

    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.
  2. Experimental, Investigational, or Unproven

    1. Aetna considers intraoperative EEG experimental, investigational, or unproven for open-heart surgery and for all other indications not listed above (e.g., prediction of post-operative delirium) because its clinical value has not been established.
    2. Aetna considers grid monitoring experimental, investigational, or unproven for all other indications not listed above because its clinical value for these indications has not been established.
  3. Policy Limitations and Exclusions

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

  4. Related Policies


CPT Codes / HCPCS Codes / ICD-10 Codes

Code Code Description

Information in the [brackets] below has been added for clarification purposes.   Codes requiring a 7th character are represented by "+":

Intra-operative electroencephalographic (EEG) monitoring of cerebral function during intracranial vascular surgical procedures:

CPT codes covered if selection criteria are met:

95812 Electroencephalogram (EEG) extended monitoring; 41-60 minutes
95813     greater than 1 hour
95822 Electroencephalogram (EEG); recording in coma or sleep only)
95940 Continuous intraoperative neurophysiology monitoring in the operating room, one on one monitoring requiring personal attendance, each 15 minutes (List separately in addition to code for primary procedure)
95941 Continuous intraoperative neurophysiology monitoring, from outside the operating room (remote or nearby) or for monitoring of more than one case while in the operation room, per hour (List separately in addition to code for primary procedure)

Other CPT codes related to the CPB:

31200 - 31230, 61000 - 61253, 61304 - 61576, 61590 - 61619, 61623 - 61645, 61680 - 61711, 61720 - 61791, 61850 - 61888, 62000 - 62148, 62160 - 62165, 64716, 67570, 69501 69530, 69601 - 69605, 69635 - 69646, 69666 - 69667, 69720 - 69745, 69805 - 69806, 69910 - 69915, 69950 - 69955 Intracranial vascular surgical procedures

HCPCS codes covered if selection criteria are met:

G0453 Continuous intraoperative neurophysiology monitoring, from outside the operating room (remote or nearby), per patient, (attention directed exclusively to one patient) each 15 minutes (list in addition to primary procedure)

ICD-10 codes covered if selection criteria are met:

C71.3 Malignant neoplasm of parietal lobe [parietal tumor]
C79.31 Secondary malignant neoplasm of brain [parietal tumor]
D33.0 Benign neoplasm of brain, supratentorial [parietal tumor]
D43.0 Neoplasm of uncertain behavior of brain, supratentorial [parietal tumor]
D49.6 Neoplasm of unspecified behavior of brain [parietal tumor]
G93.89 Other specified disorders of brain [lesion near the eloquent cortex]

Intra-operative electroencephalographic (EEG) monitoring of cerebral function during carotid artery surgery:

CPT codes covered if selection criteria are met:

95955 Electroencephalogram (EEG) during non-intracranial surery (eg, carotid)

Other CPT codes related to this CPB:

37236 - 37237, 37242, 33510, 33889, 33891, 34001, 34151, 35001 - 35002, 35121 - 35122, 35301, 35341, 35390, 35501, 35506, 35508 - 35512, 35515 - 35516, 35518, 35521 - 35523, 35525 - 35526, 35531, 35601, 35606, 35642, 35691, 35694 - 35695, 35701, 36100, 36221 - 36224, 36227 -36228, 36595, 37215 - 37218, 37600, 37605 -37606, 60600, 60605, 61590 - 61592, 61596, 61611, 61710 Carotid artery surgery

ICD-10 codes not covered for indications listed in the CPB :

F05 Delirium due to known physiological condition [post-operative delirium]

Grid Monitoring (Electrocorticography, ECoG) :

CPT codes covered if selection criteria are met:

95829 Electrocorticogram at surgery (separate procedure)

Other CPT codes related to this CPB:

61531 Subdural implantation of strip electrodes through one or more burr or trephine hole(s) for long term seizure monitoring
61533 Craniotomy with elevation of bone flap; for subdural implantation of an electrode array, for long-term seizure monitoring
61535     for removal of epidural or subdural electrode array, without excision of cerebral tissue (separate procedure)
61760 Stereotactic implantation of depth electrodes into the cerebrum for long term seizure monitoring
95812 - 95830 Electroencephalography (EEG)
95954 - 95967 Special EEG Tests
95961 Functional cortical and subcortical mapping by stimulation and/or recording of electrodes on brain surface, or of depth electrodes, to provoke seizures or identify vital brain structures; initial hour of attendance by a physician or other qualified health care professional
+95962     each additional hour of attendance by a physician or other qualified health care professional (List separately in addition to code for primary procedure)

Other HCPCS codes related to the CPB:

S8040 Topographic brain mapping

ICD-10 codes covered if selection criteria are met:

G40.00 - G40.919 Epilepsy and recurrent seizures
R56.1 Post traumatic seizures
R56.9 Unspecified convulsions


Standard scalp electroencephalography measures and records the electrical activity of the brain by placing electrodes on the scalp/head; most commonly used when a physician is trying to establish the presence of a seizure disorder.

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.

Prediction of Post-Operative Delirium

Fritz and colleagues (2016) stated that post-operative delirium is a common complication associated with increased morbidity and mortality, longer hospital stays, and greater health care expenditures.  Intra-operative EEG slowing has been associated previously with post-operative delirium, but the relationship between intra-operative EEG suppression and post-operative delirium has not been investigated.  In this observational cohort study, a total of 727 adult patients who received general anesthesia with planned intensive care unit (ICU) admission were included.  Duration of intra-operative EEG suppression was recorded from a frontal EEG channel (FP1 to F7).  Delirium was assessed twice-daily on post-operative days 1 through 5 with the Confusion Assessment Method for the ICU. Thirty days after surgery, quality of life (QOL), functional independence, and cognitive ability were measured using the Veterans RAND 12-item survey, the Barthel index, and the PROMIS Applied Cognition-Abilities-Short Form 4a survey.  Post-operative delirium was observed in 162 (26 %) of 619 patients assessed.  When these researchers compared patients with no EEG suppression with those divided into quartiles based on duration of EEG suppression, patients with more suppression were more likely to experience delirium (χ(4) = 25, p < 0.0001).  This effect remained significant after these investigators adjusted for potential confounders (odds ratio [OR] for log(EEG suppression) 1.22 (99 % confidence interval [CI]:, 1.06 to 1.40, p = 0.0002] per 1-minute increase in suppression); EEG suppression may have been associated with reduced functional independence (Spearman partial correlation coefficient -0.15, p = 0.02); but not with changes in QOL or cognitive ability.  Predictors of EEG suppression included greater end-tidal volatile anesthetic concentration and lower intra-operative opioid dose.  The authors concluded that EEG suppression is an independent risk factor for post-operative delirium.  Moreover, they stated that future studies should examine if anesthesia titration to minimize EEG suppression decreases the incidence of post-operative delirium.

This study has several major drawbacks:

  1. because this was an observational study, the findings cannot indicate whether the relationship between EEG suppression and delirium is causal.  Delirium was assessed as part of routine clinical care, and such assessments have limited sensitivity despite high specificity,
  2. some patients either left the ICU prior to the first delirium assessment or were sedated at all assessment time points,
  3. the post-discharge outcomes may be limited due to incomplete survey responses, particularly because patients who experienced post-operative delirium were less likely to return the survey,
  4. the Barthel Index was not performed pre-operatively, and thus it was not possible to distinguish whether patients who experienced EEG suppression had reduced functional independence before surgery as well, and
  5. this study also restricted its focus to patients with planned ICU admission after surgery, so care should be taken when applying these results to a broader surgical patient population. 

This  research group is currently conducting the ENGAGES clinical trial (NCT02241655), which may shed further light on the association between intra-operative burst suppression and post-operative delirium.

Prediction of Emergence Agitation After Sevoflurane Anesthesia

Jang and colleagues (2018) noted that emergence agitation (EA) is common after sevoflurane anesthesia, but there are no definite predictors.  In a prospective, predictive study, these researchers examined if intra-operative EEG can indicate the occurrence of EA in children.  EEG-derived parameters (spectral edge frequency 95, beta, alpha, theta, and delta power) were measured at 1.0 minimum alveolar concentration (MAC) and 0.3 MAC of end-tidal sevoflurane (EtSEVO) in 29 patients.  EA was evaluated using an EA score (EAS) in the post-anesthetic care unit on arrival (EAS 0) and at 15 and 30 minutes after arrival (EAS 15 and EAS 30).  The correlation between EEG-derived parameters and EAS was analyzed using Spearman correlation, and receiver-operating characteristic curve analysis was used to measure the predictability.  EA occurred in 11 patients.  The alpha power at 1.0 MAC of EtSEVO was correlated with EAS 15 and EAS 30.  The theta/alpha ratio at 0.3 MAC of EtSEVO was correlated with EAS 30.  The area under the receiver-operating characteristic curve of percentage of alpha bands at 0.3 MAC of EtSEVO and the occurrence of EA was 0.672.  The authors concluded that children showing high-alpha powers and low theta powers (= low theta/alpha ratio) during emergence from sevoflurane anesthesia were at high risk of EA in the post-anesthetic care unit.  These preliminary findings need to be validated by well-designed studies.

Intraoperative Electroencephalography During Parietal Tumor Resection

Mueller et al (1996) examined the usefulness of functional magnetic resonance imaging (fMRI) to map cerebral functions in patients with frontal or parietal tumors.  Charts and images of patients with cerebral tumors or vascular malformations who underwent fMRI with an echoplanar technique were reviewed.  The fMRI maps of motor (11 patients), tactile sensory (12 patients), and language tasks (4 patients) were obtained.  The location of the fMRI activation and the positive responses to intra-operative cortical stimulation were compared.  The reliability of the paradigms for mapping the rolandic cortex was evaluated.  Rolandic cortex was activated by tactile tasks in all 12 patients and by motor tasks in 10 of 11 patients.  Language tasks elicited activation in each of the 4 patients.  Activation was obtained within edematous brain and adjacent to tumors.  fMRI in 3 cases with intra-operative electrocortical mapping results showed activation for a language, tactile, or motor task within the same gyrus in which stimulation elicited a related motor, sensory, or language function.  In patients with greater than 2 cm between the margin of the tumor, as revealed by MRI, and the activation, no decline in motor function occurred from surgical resection.  The authors concluded that fMRI of tactile, motor, and language tasks was feasible in patients with cerebral tumors; fMRI showed promise as a means of determining the risk of a post-operative motor deficit from surgical resection of frontal or parietal tumors.

Karatas et al (2004) noted that cases with intractable epilepsy may present with multiple lesions in their brains.  Ictal- electroencephalography (EEG) carries a great value in identification of the primary epileptogenic source.  On the other hand, removal of low-grade tumors located around the eloquent cortex may be risky with conventional techniques.  Functional-neuronavigation (f-NN) is the integration of fMRI and stereotactic technologies; and provides interactive data regarding localization of the motor cortex.  This report presented a case with dysembryoplastic neuro-epithelial tumor (DNET), which was removed using f-NN and electrocorticography (ECoG) techniques.  A 19-year old patient with intractable complex partial and secondary generalized seizures was presented; MRI revealed a low-grade tumor located in right parietal region just behind the motor cortex, and a contralateral temporal arachnoid cyst.  Ictal-EEG demonstrated the right parietal origin of the seizures.  The patient underwent a right parietal craniotomy and tumor excision using f-NN and ECoG techniques intraoperatively.  ECoG findings correlated with epileptogenicity of the parietal lesion.  Post-operative course was uneventful; no post-operative deficit was observed.  The patient was seizure-free in 8 months follow-up.  Pathological examination reported the lesion as DNET.  The authors concluded that ictal-EEG had a very important role in identification of the epileptogenic focus in cases with multiple brain lesions.  Preservation of the functional cortex was the most prominent aim during lesional surgery of epilepsy.  Intra-operative mapping using f-NN and ECoG supported the orientation of the neurosurgeon to the functional and epileptogenic cortical areas; and thus, increased the safety and efficacy of surgical procedures.

Maesawa et al (2016) stated that few studies have examined the clinical characteristics of patients with lesions in the deep parietal operculum facing the sylvian fissure, the region recognized as the secondary somatosensory area (SII).  Moreover, surgical approaches in this region are challenging.  These investigators reported on a patient presenting with SII epilepsy with a tumor in the left deep parietal operculum.  The patient was a 24-year old man who suffered daily partial seizures with extremely uncomfortable dysesthesia and/or occasional pain on his right side.  MRI revealed a tumor in the medial aspect of the anterior transverse parietal gyrus, surrounding the posterior insular point.  Long-term video-EEG monitoring with scalp electrodes (for determination of epileptogenesis) failed to show relevant changes to seizures.  Resection with cortical and subcortical mapping under awake conditions was performed.  A negative response to stimulation was observed at the subcentral gyrus during language and somatosensory tasks; thus, the transcortical approach (specifically, a trans-subcentral gyral approach) was used through this region.  Subcortical stimulation at the medial aspect of the anterior parietal gyrus and the posterior insula around the posterior insular point elicited strong dysesthesia and pain in his right side, similar to manifestation of his seizure.  The tumor was completely removed and pathologically diagnosed as pleomorphic xantho-astrocytoma.  His epilepsy disappeared without neurological deterioration post-operatively.  In this case study, 3 points were clinically significant.  First, the clinical manifestation of this case was quite rare, although still representative of SII epilepsy.  Second, the location of the lesion made surgical removal challenging, and the trans-subcentral gyral approach was useful when intra-operative mapping was performed during awake surgery.  Third, intra-operative mapping demonstrated that the patient experienced pain with electrical stimulation around the posterior insular point.  Thus, this report demonstrated the safe and effective use of the trans-subcentral gyral approach during awake surgery to resect deep parietal opercular lesions, clarified electrophysiological characteristics in the SII area, and achieved successful tumor resection with good control of epilepsy.

Yao et al (2018) noted that using intra-operative ECoG to identify epileptogenic areas and improve post-operative seizure control in patients with low-grade gliomas (LGGs) remains inconclusive.  These researchers retrospectively reported on a surgery strategy that was based on intra-operative ECoG monitoring.  A total of 108 patients with LGGs presenting at the onset of refractory seizures were included.  Patients were divided into 2 groups.  In Group I, all patients underwent gross-total resection (GTR) combined with resection of epilepsy areas guided by intra-operative ECoG, while patients in Group II underwent only GTR.  Tumor location, tumor side, tumor size, seizure-onset features, seizure frequency, seizure duration, pre-operative anti-epileptic drug therapy, intra-operative electrophysiological monitoring, post-operative Engel class, and histological tumor type were compared between the 2 groups.  Univariate analysis demonstrated that tumor location and intra-operative ECoG monitoring correlated with seizure control.  There were 30 temporal lobe tumors, 22 frontal lobe tumors, and 2 parietal lobe tumors in Group I, with 18, 24, and 12 tumors in those same lobes, respectively, in Group II (p < 0.05).  In Group I, 74.07 % of patients were completely seizure-free (Engel Class I), while 38.89 % in Group II (p < 0.05).  In Group I, 96.30 % of the patients achieved satisfactory post-operative seizure control (Engel Class I or II), compared with 77.78 % in Group II (p < 0.05).  Intra-operative ECoG monitoring indicated that in patients with temporal lobe tumors, most of the epileptic discharges (86.7 %) were detected at the anterior part of the temporal lobe.  In these patients with epilepsy discharges located at the anterior part of the temporal lobe, satisfactory post-operative seizure control (93.3 %) was achieved after resection of the tumor and the anterior part of the temporal lobe.  The authors concluded that intra-operative ECoG monitoring provided the exact location of epileptogenic areas and significantly improved post-operative seizure control of LGGs.  In patients with temporal lobe LGGs, resection of the anterior temporal lobe with epileptic discharges was sufficient to control seizures.

Maesawa et al (2018) stated that epilepsy surgery aims to control epilepsy by resecting the epileptogenic region while preserving function.  In some patients with epileptogenic foci in and around functionally eloquent areas, awake surgery is implemented.  These investigators analyzed the surgical outcomes of such patients and discussed the clinical application of awake surgery for epilepsy.  They examined a total of 5 consecutive patients, in whom these researchers performed lesionectomy for epilepsy with awake craniotomy, with post-operative follow-up of greater than 2 years.  All patients showed clear lesions on MRI in the right frontal (n = 1), left temporal (n = 1), and left parietal lobe (n = 3).  Intra-operatively, under awake conditions, sensorimotor mapping was performed; primary motor and/or sensory areas were successfully identified in 4 cases, but not in 1 case of temporal craniotomy.  Language mapping was performed in 4 cases, and language areas were identified in 3 cases.  In 1 case with a left parietal arterio-venous malformation (AVM) scar, language centers were not identified, probably because of a functional shift.  Electrocorticograms (ECoGs) were recorded in all cases, before and after resection; ECoG information changed surgical strategy during surgery in 2 of 5 cases.  Post-operatively, no patient demonstrated neurological deterioration.  Seizure disappeared in 4 of 5 cases (Engel class 1), but recurred after 2 years in the remaining patient due to tumor recurrence.  Therefore, for patients with epileptogenic foci in and around functionally eloquent areas, awake surgery allowed maximal resection of the foci; intra-operative ECoG evaluation and functional mapping allowed functional preservation.  This led to improved seizure control and functional outcomes.


The above policy is based on the following references:

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