The overall goal of this procedure is to construct and analyze the connectivity patterns in a map of cortical interactions built with the recordings from foramen ovale electrodes of patients suffering from temporal lobe epilepsy. This method can help answer key questions in the epilepsy field. As why, how the seizure originate in the epileptic network.
The main advantage of this technique is that the inner part of the epileptic network can be accessed by using a semi-invasive method at foramen ovale electrodes. Generally, individuals new to this method will struggle because of the highly interdisciplinary requirements needed to retain data from foramen ovale electrodes and properly analyze them on their network approach. We first have the idea for this method when we realized that ipsilateral low levels of synchronization were tightly related with seizure appearance in the same temporal site of the brain.
Begin by explaining the experimental procedure to the patient, and answer any questions. Then, obtain a signed informed consent form. Next, place the patient on the operating table in a supine position, with their neck gently extended at 15 degrees.
The foramen ovale is allocated in the posterior part of the greater wing of this sphenoid bone. For a correct needle introduction, mark the skin with a marker according to Hartel's landmarks, such that the entry point is approximately three centimeters lateral to the ipsilateral side of the oral commissure toward two points. One, immediately inferior to the ipsilateral pupil and the anterior posterior plane, and the other approximately 2.5 centimeters anterior to the external auditory meatus in the lateral plane.
Prepare the patient's cheek with an iodine solution, starting at the incision site and circling outward. Then, drape the area immediately surrounding the incision site. Puncture the skin with a 20 gauge spinal needle.
Put the finger just behind the last molar as a guide for the needle. Next, advance the needle toward the region of the foramen ovale under fluoroscopic guidance. Use the lateral views provided by the fluoroscopy images to determine the position of the needle tip.
When the needle passes the foramen ovale, remove the stylette and replace it with a six-contact foramen ovale electrode, or FOE. The electrode should pass through the foramen ovale close to the mandibular nerve, entering into the cranial cavity. Finally, position the electrode in the ambient cistern, recording from the mesial temporal lobe area.
Then, assess correct implantation of the FOE. After the FOEs are correctly positioned in the ambient cisterns, secure them to the skin with drapes. Finally, wake up the patient and lead them to the recovery room.
Lead the patient to the video electroencephalography, or VEEG room, for a stay of approximately five days. Mark the point 10%of the distance above the nasion, the Fpz electrode. Mark the Cz electrode to locate the FC position and complete the rest of the electrodes.
Next, clean and dry the skin. Place a moderate amount of collodion with conductive gel in each electrode cup and position the electrodes in the prepped areas. Dry the collodion with a hair dryer.
Connect all scalp electrodes and FOE wires to the electrode box, which is connected to an electroencephalographer. Ensure that the scalp electrode impedances are under 10 kilo-ohms and that all electrode signals are good. Then, acquire digital scalp EEG data and FOE data at 1, 024 hertz, using a video-synchronized electroencephalographer.
Use both interictal paroxysmal and ictal activities to approximately locate the ictogenic area. Identify the electrodes where epileptogenic elements appear, including the slow wave complex, polyspikes, runs of rapid spikes, sharp waves, sharp and slow wave complex, slow sharp waves, spikes, and spike and slow waves. Record the times of seizure onset and end as well as any other clinical signs or occurrences relevant to the study.
Finally, using stored data, run the numerical code to construct the cortical network to visualize the several network parameters and calculate the synchronization pattern. In this figure, notice that typical raw scalp and FOE signals show the appearance of a seizure at the left FOE, which spreads to the scalp and right FOE contacts. Here, a representation of the epileptogenic activity is shown during the transition from pre-ictal to the ictal and post-ictal periods.
Temporal dynamics of several network measures during the transition from the pre-ictal to the ictal and post-ictal stages. DOL and ACC values were higher during the seizure, with a decrease in the APL and MOD, suggesting an increase in the overall connectivity. There is a connectivity imbalance during both the interictal and the ictal periods, with lower ipsilateral connectivity as shown by the lower density of lines in the left FOE as compared with the density of lines in the right FOE.
The last figure shows raw EEG signals in the corresponding connectivity pattern between the electrodes. Most of the time, there is a decrease in the mesial connectivity ipsilateral to the seizure onset side, the left one. This lower ipsilateral connectivity exists during the pre-ictal stage as well as during the seizure.
A dramatic increase in the overall connectivity during and after the seizure is readily apparent in the number of links, as well as in the thickness of them. The connectivity progressively decreases during the post-ictal period. To properly perform this procedure, a well-trained interdisciplinary team is required with a fluid and informative communication between them.
Is that the way that anyone knows the needs and wants of anyone else. While attempting this procedure, it is important to remember the heuristic feature of the technique, which is mainly devised to identify the epileptic zone of unilateral mesial temporal lobe epilepsy patients. Following this procedure, other methods like spectroanalysis can be performed in order the answer additional questions like which frequency band predominate during seizures.
The use of both network theory and foramen ovale electrodes allows a fast and robust analysis of the connectivity imbalance in the mesial areas of temporal lobe epilepsy patients. After watching this video, you should have a good understanding of how to successfully perform the foramen ovale electrode implantation surgery and complete a network analysis of cortical activity. Don't forget that FOE implantation surgery may become extremely difficult and precaution sets up precise fluoroscopic guidance and a good post-surgical evaluation of the electrode placements would always be done when performing this procedure.
