Electrocorticography (ECoG) uses epidural or subdural electrode arrays to record the electroencephalogram (EEG) from the cerebral cortex. ECoG is an invasive procedure; a craniotomy is required for implantation of the electrodes. The purpose of ECoG is to localize a suspected seizure focus in the cerebral cortex in patients who are candidates for surgery.

Extraoperative electrocorticography is considered medically necessary on a prior approval basis for the purpose of recording seizures. Prior to undergoing ECoG, the patient must:

• have debilitating seizures intractable to anticonvulsant medication;
• have undergone standard testing that does not clearly localize a seizure focus but does indicate strongly the presence of a focus; and
• the suspected seizure focus must be in an area of the brain that is accessible for surgery.

Extraoperative ECoG is considered investigational for stimulation and recording in order to determine electrical thresholds of neurons as an indicator of seizure focus.

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Intraoperative ECoG is a long-standing technique used to map abnormal brain tissue in the motor and/or sensory cortex prior to resection of the abnormal tissue. As such, intraoperative ECoG is an integral part of the surgical procedure and is not eligible for coverage as a separate procedure.

For the purposes of concurrent review, high frequency of recording sessions or long duration of implantation may indicate that the ECoG is being used for stimulation and recording to determine neuronal thresholds. EEGs that result from such sessions may show stimulation artifacts that would not occur if EEG recording was performed without stimulation. However, such stimulation artifacts can be filtered out in the recording process and, therefore, will not always be evident in the EEG.

A search of the literature was completed through the MEDLINE database for the period of January 1992 through October 1995. The search strategy focused on references containing the following Medical Subject Headings:

– Electrocorticography
 
– Electroencephalography

Research was limited to English-language journals on humans.

See also:

Technology Evaluation and Coverage 1988: p. 212

Electrocorticography
Electroencephalography