Electrocorticography

Electrocorticography

1. ELECTROCORTICOGRAPHYELECTROCORTICOGRAPHY
(ECOG)(ECOG)
Syed Ahmed Imran
Senior Neurophysiology Technologist
BSc,DCN,REEGT,CNIM
King Faisal Specialist Hospital
Riyadh, Saudi Arabia

2. What is ECOG?What is ECOG?
ECOG is a neurophysiologic technique
that records cortical electrical potentials
directly from the surface of the brain.

3. Why we do ECOG?Why we do ECOG?
To determine the site and borders of
epileptogenicity and offers predictive
information about post surgical outcome.

4. Types of ECOG recording?Types of ECOG recording?
Intraoperative Recording
Extraoperative Recording

6. Intraoperative RecordingIntraoperative Recording
Intraoperative ECOG refers to the
recording of neurophysiologic potentials
directly from the brain within the
confines of the operating room.
When used as a presurgical tool,
intraoperative ECOG is limited because
of the brief opportunity for recording
during surgery.

7. Intraoperative RecordingIntraoperative Recording
ECOG is recorded with standard EEG
equipment brought to the operating room.
Seizures are rarely recorded in utilizing
ECOG.
The IED provide bulk of information
obtained within the OR.
IOECOG has been used in an effort to
localize the site of epileptogenicity through
the demonstration of IED persistence,
frequency, and distribution.

8. Points to note in IOECOGPoints to note in IOECOG
Functional relationship between IED and
seizure onset are not always
commensurate (equal).
Furthermore, spikes and sharp waves
that are propagated or even volume
conducted are not readily distinguishable
from spikes and sharp waves involved in
the primary generator.
Hence seizure may arise from sites
outside the ECOG sites of IED.

10. Extraoperative RecordingExtraoperative Recording
Extraoperative ECOG allows clarification
of briefer Intraoperative recordings by
increasing the length of recording and
obtaining information from intracranial
ictal EEGs.
It also allows more prolonged cortical
mapping time when necessary.

11. Points to note in ExECOGPoints to note in ExECOG
Intraparenchymal (Intracortical or depth) or
Extraparenchymal (Subdural strip/grid)
recordings are used during the intracranial
phase of epilepsy monitoring.
Deep seated anatomic structures, including
the hippocampus, amygdala, and subcortical
abnormalities within the brain, may serve as
generators for seizures.
Placement of depth electrodes near these
generators allow for more accurate
localization.

12. Types of ElectrodesTypes of Electrodes
Subdural electrodes are available in
various configuration that comprise grid
and strip electrodes.
Stainless steel and platinum alloys are the
principal compounds composing the
electrodes.
They are embedded in a clear malleable
silicon or polyurethane array to permit
visualization of underlying cortical
structures during placement.

13. Types of ElectrodesTypes of Electrodes
Variety of electrode styles are available,
typically include strips with 2 to 8
contacts and grids that contain 16 to 64
contacts.
Each contact is 5mm wide in diameter
and spaced 1cm apart.

15. Points to note for electrodesPoints to note for electrodes
The advantage of subdural electrodes over
depth electrodes are that they are less likely
to create morbidity, are easier to implant,
and can cover a large cortical surface.
Depth electrodes are intraparenchymal
electrodes that sample a small surrounding
area of brain at the site of placement.
Depth electrodes have the advantage to
allow more precise localization from the
mesial temporal structures.

16. Technique to perform ECOGTechnique to perform ECOG
After the patient is taken to the OR and has
undergone general anesthesia, the head is
secured using Mayfield pin holders, shaved,
prepped and draped in a sterile fashion.
A craniotomy is performed to expose the
dura mater, which is then opened to expose
the cortical surface for placement of
electrodes.
The placement of subdural grid requires a
craniotomy, while strip electrodes may be
placed through individual burr holes.

17. Technique to perform ECOGTechnique to perform ECOG
Recording ECOG inside and outside the
OR uses the same technique.
A preoperative plan is developed prior to
surgery.
Selection of electrode types to be used
and plans for an implanted electrodes
array are required.
The leads from the individual electrodes
connect to the EEG machine for direct
recording in the OR.

18. Technique to perform ECOGTechnique to perform ECOG
For Extraoperative recording, the
electrode leads are tunneled under the
skin and exit through a short distance
away from the craniotomy site.
This helps minimize the risk of CSF
leakage and infection.

20. Risk of infectionRisk of infection
The risk of infection and hemorrhage
with insertion of subdural strip
electrodes is less than 1%, while grid
electrodes carry a higher risk of
complications.
Besides infection, transient neurological
deficits, hematoma, increased intracranial
pressure, cerebral infarction, and
herniation can occur by the placement of
electrodes.

21. Risk of infectionRisk of infection
The greater the number of electrodes,
the longer the recording time, the older
the patient, the greater the number of
skull breaches, or dominant hemispheric
implantation, the greater the risk of
complications.

22. Effects of anesthesia on ECOGEffects of anesthesia on ECOG

23. Samples of ECOGSamples of ECOG

31. QUESTIONS??QUESTIONS??