Epilepsy Definition: Abnormal electrical discharge originating from neuron groups in the brain is called epilepsy.
Incidence: Especially 12.5% – 25% of partial complex seizures are resistant epilepsy.
Resistant epilepsy: These are epilepsies whose seizures cannot be controlled despite adequate dose, duration, optimal antiepileptic drug blood level and appropriately selected antiepileptic drugs.
History of Epilepsy Surgery
Sir Viktor Horsley; He tried to prevent epilepsy with brain surgery for the first time in 1886,
Forster; after the First World War, he performed scar resection in traumatic epilepsy,
Falkoner; First time performing amygdala hippocampectomy,
Van vaganen; Performed the first commissurotomy,
Bogen; He performed the first callosotomy surgery.
Causes of Epilepsy
Unknown causes (possibly genetic), known ones are genetic-chromosomal abnormalities, perinatal damages, brain infections, tumors, vascular diseases, head trauma, degenerative brain diseases, metabolic and hormonal diseases , some drugs and alcohol withdrawal, others (porphyria, eclmpsia, etc.) are causes of epilepsy.
Which Patients Should Have Epilepsy Surgery?
First of all, the patient to be operated must have drug-resistant epilepsy. Seizures should be uncontrollable despite adequate blood levels of high-dose antiepileptic drugs. The emergence of unacceptable side effects of these drugs and the deterioration of the patient’s quality of life are considered in patient selection. If, despite the use of one or more antiepileptic drugs, tonic-clonic seizures or recurrent partial complex seizures prevent the person from working, driving, and social life, patients with such conditions are examined for epilepsy surgery. On the other hand, surgical treatment can be decided earlier in patients with congenital or acquired brain lesions.
In this way, patients with brain lesions show resistance to drugs and have a high success rate in epilepsy surgery. Although it is not a general rule, patients should use antiepileptic drugs properly for at least 1–2 years before deciding on epilepsy surgery. If seizures are very frequent and prevent normal life, surgical treatment can be performed within 1 year from the onset of epilepsy.
Which patients may find it difficult to perform epilepsy surgery?
1- Having a progressive disease reduces the success of epilepsy surgery.
2- The benefits and harms of epilepsy surgery should be considered in patients with severe systemic medical disease.
3- Patients with low intelligence (IQ<70) cannot undergo resective surgery, because there is usually diffuse or more than one epileptic seizure focus, which often renders the surgical outcome unsuccessful.
4- If the patient who will undergo temporal lobectomy surgery has impaired memory function in the contralateral temporal lobe in the WADA test, surgery should not be performed because severe dementia will occur in the patient after surgery.
5- If cooperation cannot be established with the patient in pre-surgical examinations, the surgical decision should be abandoned.
6- Surgery should not be decided for patients with active, chronic psychosis regardless of seizures.
Epilepsy Surgery Diagnostic Methods
Each epilepsy center applies different criteria, examination techniques and surgical approaches within the individual experience of doctors. The purpose of the review is to determine the most appropriate surgical method for each patient or to reveal any contraindications.
Epilepsy examinations consist of 4 stages;
Stage I: Noninvasive tests and video/EEG monitoring with scalp surface electrodes
Stage II: Bilateral carotid angiography and intracarotid sodium amobarbital test
Stage III: video/EEG monitoring with invasive intracranial electrodes
Stage IV: Surgical treatment
Magnetic resonance imaging (MRI) is an appropriate imaging modality for demonstrating mesial temporal sclerosis in the investigation of patients with refractory epilepsy. Positron Emission Tomography (PET) displays hypometabolism areas in 70% of patients with temporal lobe epilepsy and in approximately 60% of patients with frontal lobe epilepsy. The diagnostic accuracy of PET is quite high, and it can be mistaken if it is below 5%. SPECT, especially interictal SPECT, is less sensitive and specific than PET, and ictal SPECT is a very useful diagnostic method in identifying seizure focus, especially in patients with non-temporal lobe epilepsy.
Neuropsychological evaluation is a standard method in the pre-surgical examination of epilepsy. These tests help evaluate sensory perception, speech, memory, intellectual functions, and personality structure. Thus, it helps to localize the areas of the brain where cognitive functions are preserved or impaired. There is often a relationship between areas where cognitive functions are impaired and seizure focus.
The most important part of the preoperative stage 1 examination is long-term video/EEG monitoring with surface electrodes. Video/EEG recordings have made great contributions in demonstrating the type and location of seizures. Monitoring continues uninterrupted until at least 3 or more of their seizures are observed. The patient’s image and simultaneous EEG are recorded between the seizures and during the seizure period. The patient’s antiepileptic medications are often tapered or discontinued altogether to elicit seizures. Seizure onset focus or area is investigated by examining inter-seizure recordings and seizure EEG changes during sleep and wakefulness, and different EEG recordings. A correlation is established between the clinical features of the recorded seizures and the simultaneous EEG information. A definite localization may not be possible with surface EEG in patients with a specific epilepsy focus. Muscle and movement artifacts may be due to the bilateral symmetrical spread of discharges from the onset of seizures in deep structures to the lateral neocortical areas, or the absence of reflection of the discharges to the surface electrodes. In these cases, other examination results of the pre-surgical Stage I examination, location or side of the abnormality may be helpful.
Stage II examination: Sodium amobarbital test (WADA) test is performed with bilateral carotid angiography in patients who have completed their stage I examination and are still considered surgical candidates. With this test, the hemisphere with speech dominance is determined and the adequacy of the hemispheres for memory is measured. All information is reviewed with the epilepsy surgical team following the Stage I and Stage II pre-surgical investigations. These are patients whose specific focus cannot be determined with less harmless tests, or who cannot be safely resectioned because their seizure focus conflicts with areas with important cortical function. These patients undergo stage III examination before surgery.
Stage III examination: The patient is scheduled for recording with invasive electrodes. In line with previous investigations, only deep electrodes, subdural strip, grid, or epidural strip electrodes or a combination of these are placed in areas where seizure may occur. Deep electrodes are most successful when precise localization of patients with temporal lobe epilepsy cannot be achieved. Patients with lateral neocortical seizures can be shown more precisely with a subdural grid. Recordings made with less harmful brain electrodes are continued until at least 3 typical epileptic seizures are observed, as in recordings with surface electrodes. Video/EEG recordings are made with the same techniques as recordings with surface electrodes. There are also some complications that vary depending on the type and number of invasive brain electrodes.
Stage IV: It is applied to patients who are considered good candidates for surgery after Stage I, II and, if necessary, Stage III. Surgery is recommended by explaining the postoperative success rate and the risks that may occur during or after the surgery. In addition, the limits of the surgery can be determined by making electrocorticography recordings before or during the brain resection. Thanks to electrocorticography (EcoG), recordings are made from the surfaces of the brain or from deep structures within it. Thus, the width of the epileptogenic area can be determined according to the observed inter-seizure discharges.
Epilepsy Surgical Techniques
Anterior temporal lobectomy, Selective amygdala hippocampectomy, Callosotomy, Hemispherectomy, Multiple subpial transection, Vagal nerve stimulator are counted.
Anterior temporal lobectomy (ATL): It is the most common epilepsy surgery method with the most successful results. Surgery in the dominant hemisphere can be performed more limitedly by mapping speech functions. There are centers that prefer only selective amygdalohippocampectomy in seizures known to have mesial temporal onset. Seizure control is around 70% in ATL. However, auras may persist in 10-15% of patients. A significant improvement in seizures is observed in 20-25% of patients. There is no significant change in 10-15% of patients. As a result, a significant improvement in seizure control is seen in 85% of patients. Most patients use less medication after surgery than before surgery. Approximately 10-20% of patients’ medications are completely discontinued.
Frontal lobectomy: It is the second most frequently performed surgery after temporal lobectomy. If the frontal lobe is too large, epileptic seizures originating from one area quickly spread to multiple adjacent brain areas. Since it is difficult to record the epilepsy focus originating from deep brain structures, the location of the frontal lobe seizure focus is very difficult.
Callosotomy: This surgical method is applied to patients with drug-resistant multiple or bilateral and independent foci or in whom seizure focus cannot be identified. Seizures in which this method is most effective are atonic, tonic and tonic-clonic seizures. In many patients, surgery is performed by incision of the anterior 2/3 of the corpus callosum in order to significantly reduce the frequency of epileptic seizures. Sometimes in patients with this incision, the remaining posterior part of the corpus callosum is cut with a second attempt.
Hemispherectomy: It is a surgical technique performed in children with severe seizures originating only from one half of the brain. Before surgery, these patients typically have neurological findings such as hemiplegia, loss of touch and vision on the contralateral side of the body.
Multiple subpial transection and partial hemispherectomy: This technique was first described in 1989 by Morrel et al. With this technique, in order to ensure the integrity of the functional columns, the vertical fibers of the brain are preserved at 5 mm intervals and the horizontal fibers are cut. In this way, seizures originating from the cortical areas of the brain, which have important functions such as sensory, motor and language, are controlled or often prevented. It is reported that it does not cause significant post-operative neurological sequelae. Although the efficacy of seizure control with this technique is not well known, promising studies are reported.
In conclusion
1) Epileptic focus can be defined by investigating resistant epilepsy patients with today’s modern non-invasive or invasive examination techniques conducted by a multidisciplinary team.
2) Very successful surgical results are obtained in resistant epilepsies by applying appropriate surgical techniques to patients with defined epilepsy focus.
3) Antiepileptic drugs used by epileptic patients for a long time are reduced and discontinued and the patient is protected from the side effects of these drugs.
