Electro-corticography Systems in Surgery of the Brain

The human brain is a fantastically complicated organ. On any given day, the average man does not give much thought to this 3 pound; blood gorged, gelatinous mass stuck on his shoulders. However, the brain is responsible for controlling nearly ever human behavior and action. It is the source of all human creativity and accomplishments and everything mankind will ever achieve. It has long been known that all of this fascinating power is not distributed evenly throughout its neuronal interweave. Most brain functions are based in discreet areas, and often brain dysfunction occurs focally. These facts are critical to the modern neurosurgical approach to disease and are the basis for electrocorticography. The process of recording brain electrical activity directly from the exposed brain surface using electrodes, electrocorticography is most often used to precisely localize critical brain structures in order to avoid them when operating upon diseased areas of the brain. Additionally, electrocorticography is particularly useful while planning epilepsy surgery, as the onset and electrical propagation of a seizure may be mapped accurately. Electrocorticography may be used intraoperatively or at the bedside.

Several manufactures produce high quality advanced subdural electrode configurations allowing direct recording of electrical activity from nearly any area of the brain surface. Three companies which produce electrocorticography equipment are Ad-Tech, Astromed, and Micromar.

Ad-Tech’s Model CMU Cortical Mapping Unit is designed specifically for use in the operating room. The entire system includes a frame assembly; cranial clamp; mounting post; ground wire; sixteen sterile, disposable stainless steel, ball-tip electrode rods on flexible spring shafts; sixteen sterile, disposable spheres and one sterilization tray. It features independently positionable mounting plates; built-in adapter for Ad-Tech’s four contact strip electrodes and shielded three meter cable. Additionally, Ad-Tech’s CMU has two built-in TECH-ATTACH® connector blocks which allow easy use of Ad-Tech/Wyler brand strip or grid intraoperative electrodes.

In contrast to the Ad-Tech stainless steel electrode package, Astromed features either 16 cotton-wick (R-2) or gold ball (R-3) electrodes in a double-horn assembly. Cortical Electrode Assembly Model CE1 has each electrode in a ball and socket joint for ease in positioning and a supporting bone clamp design simplifies three dimensional adjustments.

Micromar presents yet another option with its electrocorticography electrode set consisting of 16 carbon tip electrodes housed within a composite assembly structure. The entire assembly may be attached to the skull with a mounting post for intraoperative recording. The electrodes have a ball joint and flexible wire. A clip electrode is used as a reference and pin connector diameter may be customized depending upon the EEG machine being employed.

In addition to the above systems designed for dedicated operating room use, several different types of grid or strip electrodes may be placed in the operating room and the electrocorticography performed in the less restrictive environment of a typical hospital room. Ad-Tech/Wyler subdural strip and grid electrodes are available in various dimensions, having anywhere from 4 to 64 electrode contacts. These electrodes all feature transparent, flexible bodies, barium markers, and numbers on the top row of every grid. They are available in a choice of stainless steel or platinum contacts.

Integra NeuroSciences also produces strip and grid electrodes with 4 to 64 contacts. Additionally, a 16 contact, dual-sided interhemispheric strip is available. Each implant grade stainless steel or platinum contact is mounted flush with the electrode surface and individually numbered. Strip electrodes are fitted with a gold plated mini-PC board connector; larger grids incorporate a single gold-plated Flex Connector. Electrode leads are extra long and durable to ensure reliable recording. Strip and grid electrodes have standard 1 cm spacing.

A third choice for electrocorticography recording electrodes is those produced by PMT Corporation. Any of a wide selection of special contact arrays may be shipped sterile with or without radiopaque marking. Stainless steel or platinum electrodes are numbered and are equipped with dependable connectors and cables.

Recent advances in materials and computer processing make it possible to understand the physiology of the brain at a more detailed level than ever before. Through electrocorticography brain surgery may be performed with a level of safety and precision not otherwise available.