Extratemporal Lobe Epilepsy Surgery (Progress in Epileptic Disorders)

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Both can localize certain cortical functions non-invasively but require dedicated units that are not widely available. After the resection strategy is decided upon, tissue removal is carried out using subpial resection techniques.

Cortical gray and white matter is carefully removed by suction or cavitron so that the pia remains intact over the adjacent gyri. This tends to form a nonscarring barrier and preserves blood supply to the remaining cortex as well. Following removal, some centers carry out post-resection cortical EEG recordings and may carry out further removal if considerable epileptic activity remains at the resection margins. With the advent of MRI, many patients with recurrent seizures are now discovered to have small, previously unrecognized lesions such as cavernous angiomas, low-grade astrocytomas, cortical dysplasias and areas of focal atrophy that are clearly the cause of their seizures.

In general, if these are located in extratemporal sites, removal of the lesion and a small rim of surrounding cortex is often successful in controlling seizures. Removal of significant perilesional cortex may be necessary to achieve optimal seizure control in some patients.

In many instances, if only a portion of the lesion is removed, the surgical result is suboptimal. The majority of resections involve the temporal lobe and initially consisted of the classical anterior temporal lobectomy. This was either carried out "en-bloc" under general anesthesia or using a more tailored resection with electrocorticography and cortical mapping under local anesthesia.

The majority of temporal lobectomies, whether in the dominant or nondominant hemisphere, can now be safely performed under general anesthesia with or without electrocorticography. In the dominant hemisphere, temporal lobe removals usually extend back 4. In the non-dominant hemisphere, temporal lobectomies can extend beyond 7 or 8 cm but will result in a contralateral superior quadrantanopsia because of encroachment upon the optic radiation. It is important that the mesial temporal structures are included in the removal because most neurosurgeons believe that the hippocampus is intimately involved in seizure propagation or amplification.

Studies also indicate that recurrent seizures are more likely following temporal lobectomy when the hippocampus is not removed. The so-called antero-medial temporal lobectomy with amygdalo-hippocampectomy is a modification of the classical temporal lobectomy by reducing the amount of cortical removal and extending the hippocampal resection. Morbidity and mortality figures for cortical excisions are quite low, less than 0. Specific cognitive testing may detect permanent subtle deficits consistent with the site of removal but generally these are nonspecific.

This may be acceptable if required for seizure control since it is usually unnoticed by the patient and does not interfere with normal daily living. Memory impairment has occurred with unilateral temporal removals in rare cases but this complication is avoided by preoperative testing of speech and memory function during the intracarotid amytal test.

If memory is affected by amytal injection ipsilateral to the proposed side of the temporal removal, temporal excision may be designed to spare the hippocampus and medial structures but this approaach may reduce operative success rates. Extra-temporal resections are much less commonly performed with the majority being carried out in the frontal lobe. En bloc standardized resections are not generally suitable and most surgeons guide their resections by detailed electrocorticography, both intra- and extra-operatively along with detailed cortical mapping.

Frontal resections range from localized topectomies to complete frontal lobectomies and must be carefully individualized. Identification of the primary motor cortex is essential to avoid motor deficits and anterior language cortex to avoid speech difficulties. Parietal and occipital resections are rarely carried out but may be gratifying in patients with clear structural lesions. The results of cortical excision for extratemporal epilepsy are variable depending upon patient selection and method of presurgical evaluation. Outcome statistics are not as impressive for extra- temporal resections as they are for temporal removals.

Nevertheless, extra-temporal resections including the frontoparietal and occipital regions can give excellent results. Patients with epileptic discharge limited to the lobe of resection obviously tend to do better than those with more widespread discharges. In addition, some patients have more wide spread epileptogenic zones that require multilobar resections. Hemispherectomy is another form of cortical excision that is limited to patients with congenital hemiplegia, chronic encephalitis, hemi-megalencephaly or Sturge-Weber syndrome.

These patients tend to have severe epilepsy with wide spread independent epileptic discharges that often extend to the contralateral normal hemisphere. It is only performed on patients who have a dense hemianopsia and are already hemiplegic with no fine motor activity on the affected side. The acute surgical risk is that some crude movement or sensation on the opposite side of the body would be adversely affected. A chronic complication was recognized to occur approximately 8 to 10 years after gross total hemispherectomy.

This condition called superficial cerebral hemosiderosis resulted from chronic leaking of blood into the resection cavity producing recurrent seizures, sensori-neural deafness and hydrocephalus. Residual cerebral tissue either decreases the risk of hemorrhage into the resection cavity or alternatively absorbs any blood that might leak in. Alternatives to anatomical hemispherectomy include hemispherotomy, cerebral hemicorticectomy, dural plication and ventriculoperitoneal shunting.

All of these modifications attempt to reduce the risk of superficial cerebral hemosiderosis by minimizing cortical resection while maintaining complete functional disconnection. Corpus callosotomy has been offered as an alternative to hemispherectomy in epileptic patients with congenital hemiplegia but the results are not as good as with hemispherectomy. It is indicated when the patient has a severely damaged hemisphere but motor, sensory or visual function that would be valuable to preserve. In general, however, corpus callosotomy ismost useful for those patients with generalized seizure disorders and bilateral independent epileptic areas in the frontal region.

The seizures that respond best to callosotomy are sudden falls or "drop attacks" with injury to the patient. The generalized seizures and drop attacks tend to improve markedly although a complete cure of seizures is extremely rare. Transient abulia is common following anterior callosotomy but other disconnection effects are fortunately mild and uncommon.

In patients with complete callosotomy, disconnection symptoms are more frequent. There is often some difficulty in bimanual tasks and apraxia for commands directed to the nondominant extremity. Visual presentation to the hemifield opposite to the dominant hemisphere cannot be comprehended or described by language modalities and there is often significant difficulty writing with a nondominant hand. Fortunately, most of these functional deficits are not noticeable in normal daily living and are balanced by the improved seizure control.

In patients with seizure onset or epileptic zones located in eloquent cortex, multiple vertical subpial transections have been recommended as an alternative to cortical resection. This technique leaves the vertical columnar arrangement of the cortex intact thereby preserving function but prevents spreading of the seizure discharge in the horizontal plane to reduce seizures. Stereotactic lesions of deep cerebral structures have been carried out for a variety of generalized and focal forms of epilepsy in the past.

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Frontiers | The Role of Functional Neuroimaging in Pre-Surgical Epilepsy Evaluation | Neurology

Bilateral cingulotomies, amygdalotomies, lesions in the Field of Forel and thalamic lesions have all been tried. While some lesions may have an initial good result, seizures tend to recur in virtually all patients and stereotactic ablations of subcortical structures are no longer in use. Cerebellar electrical stimulation has been used to treat generalized focal and myoclonic seizures as well as for spasticity of cerebral palsy. Initial reports of clinical success could not be reproduced. Reports followed of tissue damage from the cerebellar stimulator and a large number of late failures.

Improvement in the technical quality of the electrodes and stimulating devices has led to some renewed interest in this technique but it is not currently a recommended treatment and no definitive evidence supporting its use in controlling epilepsy is available. More recently, a number of patients with both focal and generalized intractable seizures have undergone implantation of a nerve stimulator around the left vagus nerve.

The success or failure of the surgical treatment of epilepsy depends in large part on the proper selection and investigation of patients. Recent advances in imaging and long term EEG monitoring have allowed for a greater accuracy in the localization of the seizure focus with overall surgical results better than those of the prior decades. Continued investigation into the basic mechanisms of the epilepsies as well new forms of medical and surgical therapy is necessary in order to help the many patients with severe and disabling intractable seizures.

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Definitions There are many types of seizures and different forms of epilepsy. Presurgical Evaluation The goal of epilepsy surgery is to identify an abnormal area of cortex from which the seizures originate and remove it without causing any significant functional impairment.

Quantitative MRI in refractory temporal lobe epilepsy: relationship with surgical outcomes

Clinical Features The presurgical evaluation of a patient with medically intractable epilepsy begins with a complete history and physical examination. Neuro-imaging Modern neuroimaging is crucial to surgical decision-making. Neuropsychological Testing Detailed neuropsychological testing is carried out to reveal specific focal or multifocal cognitive deficits that might be correlated with the neuroimaging and EEG. Epidural electrodes Epidural electrodes are used infrequently and generally only for lateralization and approximate localization of seizure onset.

Subdural electrodes These electrodes are placed subdurally on the surface of the brain in the form of rectangular grids or linear strips with flat metal contact points mounted in flexible plastic. Surgical Decision Making If the information obtained during the noninvasive presurgical evaluation consistently points towards a single area of the brain as being the site of seizure onset, then the patient may be taken directly to surgery for resection of that area.

Therapeutic Surgical Options Epilepsy surgery began as removal of gross structural lesions of the brain.

Definitions

General Considerations The primary objective of most epilepsy surgical procedures is to accurately localize and then completely excise the epileptogenic region without causing cognitive or neurologic deficit. Lesionectomy With the advent of MRI, many patients with recurrent seizures are now discovered to have small, previously unrecognized lesions such as cavernous angiomas, low-grade astrocytomas, cortical dysplasias and areas of focal atrophy that are clearly the cause of their seizures.

Temporal resections The majority of resections involve the temporal lobe and initially consisted of the classical anterior temporal lobectomy. Extra-temporal resections Extra-temporal resections are much less commonly performed with the majority being carried out in the frontal lobe.

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Podcast: Temporal Lobectomy Epilepsy Surgery

Multiple subpial transection for intractable partial epilepsy: An international meta-analysis. Multiple subpial transections: Outcome and complications in 20 patients who did not undergo resection.

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