Failure of low-dose radiosurgery to control temporal lobe epilepsy

A Potential Risk of Radiation-Induced Cavernous Malformations Following Adjuvant Gamma Knife Radiosurgery for Mesial Temporal Lobe Epilepsy

OBJECTIVE

Several clinical studies have explored the feasibility and efficacy of radiosurgical treatment for mesial temporal lobe epilepsy, but the long-term safety of this treatment has not been fully characterized. This study aims to report and describe radiation-induced cavernous malformation as a delayed complication of radiosurgery in epilepsy patients.

METHODS

The series includes 20 patients with mesial temporal lobe epilepsy who underwent Gamma Knife radiosurgery (GKRS). The majority received a prescribed isodose of 24 Gy as an adjuvant treatment after anterior temporal lobectomy.

RESULTS

In this series, we identified radiation-induced cavernous malformation in three patients, resulting in a cumulative incidence of 18.4% (95% confidence interval, 6.3% to 47.0%) at an 8-year follow-up. These late sequelae of vascular malformation occurred between 6.9 and 7.6 years after GKRS, manifesting later than other delayed radiation-induced changes, such as radiation necrosis. Neurological symptoms attributed to intracranial hypertension were present in those three cases involving cavernous malformation. Of these, two cases, which initially exhibited an insufficient response to radiosurgery, ultimately demonstrated seizure remission following the successful microsurgical resection of the cavernous malformation.

CONCLUSION

All things considered, the development of radiation-induced cavernous malformation is not uncommon in this population and should be acknowledged as a potential long-term complication. Microsurgical resection of cavernous malformation can be preferentially considered in cases where the initial seizure outcome after GKRS is unsatisfactory.

Minimally Invasive Destructive, Ablative, and Disconnective Epilepsy Surgery

Conventional epilepsy surgery performed by microsurgical dissection typically requires large cranial working windows created with high-speed drills and lengthy incisions. In the past few decades, minimally invasive techniques have been developed with smaller incisions, comparable efficacy, shorter hospitalizations, and better safety profiles. These minimally invasive alternatives utilize stereotactic, ultrasonic, radiotherapeutic, and endoscopic techniques. Although not able to completely replace conventional surgery for all etiologies of epilepsy, these minimally invasive techniques have revolutionized modern epilepsy surgery and have been an invaluable asset to the neurosurgeon's repertoire. The endoscope has allowed for surgeons to have adequate visualization during resective and disconnective epilepsy surgeries using keyhole or miniature craniotomies. Modern stereotactic techniques such as laser interstitial thermal therapy and radiofrequency ablation can be used as viable alternatives for mesial temporal lobe epilepsy and can destroy lesional tissue deep areas without the approach-related morbidity of microsurgery such as with hypothalamic hamartomas. These stereotactic techniques do not preclude future surgery in the settings of treatment failure and have been used successfully after failed conventional surgery. Multiple ablation corridors can be performed in a single procedure that can be used for lesioning of large targets or to simplify treating multifocal epilepsies. These stereotactic techniques have even been used successfully to perform disconnective procedures such as hemispherotomies and corpus callosotomies. In patients unable to tolerate surgery, stereotactic radiosurgery is a minimally invasive option that can result in improved seizure control with minimal procedural risks. Advances in minimally invasive neurosurgery provide viable treatment options for drug-resistant epilepsy with quicker recovery, less injury to functional brain, and for patients that may otherwise not choose conventional surgery.

Epilepsy

GKNS has been introduced as an alternative to microsurgery for the treatment of certain types of focal epilepsy. It was first noted that epilepsy associated with AVMs often improved before the obliteration of the vascular lesion. It was subsequently shown that the treatment could be effective in mesial temporal lobe epilepsy (MTLE) producing remission in around 60% of patients, provided the treatment was carried out as originally designed. GKNS has also been useful in the treatment of gelastic epilepsy associated with hypothalamic hamartomas.

Radiosurgery versus open surgery for mesial temporal lobe epilepsy: The randomized, controlled ROSE trial

OBJECTIVE

To compare stereotactic radiosurgery (SRS) versus anterior temporal lobectomy (ATL) for patients with pharmacoresistant unilateral mesial temporal lobe epilepsy (MTLE).

METHODS

This randomized, single-blinded, controlled trial recruited adults eligible for open surgery among 14 centers in the USA, UK, and India. Treatment was either SRS at 24 Gy to the 50% isodose targeting mesial structures, or standardized ATL. Outcomes were seizure remission (absence of disabling seizures between 25 and 36 months), verbal memory (VM), and quality of life (QOL) at 36-month follow-up.

RESULTS

A total of 58 patients (31 in SRS, 27 in ATL) were treated. Sixteen (52%) SRS and 21 (78%) ATL patients achieved seizure remission (difference between ATL and SRS = 26%, upper 1-sided 95% confidence interval = 46%, P value at the 15% noninferiority margin = .82). Mean VM changes from baseline for 21 English-speaking, dominant-hemisphere patients did not differ between groups; consistent worsening occurred in 36% of SRS and 57% of ATL patients. QOL improved with seizure remission. Adverse events were anticipated cerebral edema and related symptoms for some SRS patients, and cerebritis, subdural hematoma, and others for ATL patients.

SIGNIFICANCE

These data suggest that ATL has an advantage over SRS in terms of proportion of seizure remission, and both SRS and ATL appear to have effectiveness and reasonable safety as treatments for MTLE. SRS is an alternative to ATL for patients with contraindications for or with reluctance to undergo open surgery.

New Techniques and Progress in Epilepsy Surgery

While open surgical resection for medically refractory epilepsy remains the gold standard in current neurosurgical practice, modern techniques have targeted areas for improvement over open surgical resection. This review focuses on how a variety of these new techniques are attempting to address these various limitations. Stereotactic electroencephalography offers the possibility of localizing deep epileptic foci, improving upon subdural grid placement which limits localization to neocortical regions. Laser interstitial thermal therapy (LITT) and stereotactic radiosurgery can minimally or non-invasively ablate specific regions of interest, with near real-time feedback for laser interstitial thermal therapy. Finally, neurostimulation offers the possibility of seizure reduction without needing to ablate or resect any tissue. However, because these techniques are still being evaluated in current practice, there are no evidence-based guidelines for their use, and more research is required to fully evaluate their proper role in the current management of medically refractory epilepsy.

Fractionated Stereotactic Gamma Knife Radiosurgery for Medial Temporal Lobe Epilepsy: A Case Report

An 18-year-old left-handed male harbored intractable medial temporal lobe epilepsy (MTLE) underwent fractionated gamma knife surgery (GKS) instead of open surgery, considering the mental retardation and diffuse cerebral dysfunction. GKS treatment parameters were: target volume, 8.8 cm³; total marginal dose, 24 Gy in 3 fractionations at the 50% isodose line. The patient has been free from seizures since 9 months after GKS, with notable improvement in cognitive outcome. Fractionated GKS could be considered as a safe tool for seizure control and neuropsychological improvement in patients with MTLE.

Radiosurgery for Medial Temporal Lobe Epilepsy Resulting from Mesial Temporal Sclerosis

Medial temporal lobe epilepsy associated with mesial temporal sclerosis (MTS) is perhaps the most well-defined epilepsy syndrome that is responsive to structural interventions such as surgery. Several minimally invasive techniques have arisen that provide additional options for the treatment of MTS while potentially avoiding many of open surgery's associated risks. By evading these risks, they also open up treatment options to patients who otherwise are poor surgical candidates. Radiosurgery is one of the most intensively studied of these alternatives and has found a growing role in the treatment of medial temporal lobe epilepsy.

Morphological changes after radiosurgery for mesial temporal lobe epilepsy

Background

To review our experience with morphological developments during the long-term follow-up of patients treated by Gamma Knife radiosurgery for mesial temporal lobe epilepsy.

Method

Between 1995 and 1999, we treated 14 patients with marginal doses of 24 Gy (n = 6) and 18–20 Gy (n = 8). Nine of these were operated on for insufficient seizure control. We reviewed seizure outcome and magnetic resonance images in both operated and unoperated patients and also re-examined histopathology specimens.

Results

Of the nine operated patients, two were Engel IIIA, one was IVA, five were IVB, and one was Engel IVC prior to surgery. At their final visit, five cases had become Engel class IA, one patient was ID, and two were IIC. In one patient the follow-up was not long enough for classification. Of the five unoperated patients, one was Engel class IB, one was IIIA, one IIB and one IVB at their final visit. Radionecrosis developed in 11 patients, occurring more often and earlier in those treated with higher doses. Collateral edema reached outside the temporal lobe in six patients, caused uncal herniation in two and intracranial hypertension in three. During longer follow-up, postnecrotic pseudocysts developed in 9 patients, and postcontrast enhancement persisted for 2.5–16 years after GKRS in all 14 patients. In five of them we detected its progression between 2 and 16 years after treatment. Signs of neoangiogenesis were found in two patients and microbleeds could be seen in five. Histopathology revealed blood vessel proliferation and macrophage infiltration.

Conclusions

Early delayed complications and morphological signs suggesting a risk of development of late delayed complications are frequent after radiosurgery for mesial temporal lobe epilepsy. Together with its unproven antiseizure efficacy, these issues should be taken into account when planning future studies of this method.

Electronic supplementary material

The online version of this article (doi:10.1007/s00701-015-2525-2) contains supplementary material, which is available to authorized users.

Gamma Knife radiosurgery for recurrent or residual seizures after anterior temporal lobectomy in mesial temporal lobe epilepsy patients with hippocampal sclerosis: long-term follow-up results of more than 4 years

OBJECT

Gamma Knife radiosurgery (GKRS) has proven efficacy in the treatment of drug-resistant mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS) and is comparable to conventional resective surgery. It may be effective as an alternative treatment to reoperation after failed temporal lobe surgery in patients with MTLE-HS. The purpose of this study was to investigate the efficacy of GKRS in patients with unilateral MTLE-HS who did not achieve seizure control or had recurrent seizures after anterior temporal lobectomy (ATL).

METHODS

Twelve patients (8 males; mean age 35.50 ± 9.90 years) with MTLE-HS who underwent GKRS after failed ATL (Engel Classes III-IV) were included. GKRS targets included the remnant tissue or adjacent regions of the previously performed ATL with a marginal dose of 24-25 Gy at the 50% isodose line in all patients. Final seizure outcome was assessed using Engel's modified criteria during the final 2 years preceding data analysis. A comparison between signal changes on follow-up MRI and clinical outcome was performed.

RESULTS

All patients were followed up for at least 4 years with a mean duration of 6.18 ± 1.77 years (range 4-8.8 years) after GKRS. At the final assessment, 6 of 12 patients were classified as seizure free (Engel Class Ia, n = 3; Ic, n = 2; and Id, n = 1) and 6 patients were classified as not seizure free (Engel Class II, n = 1; III, n = 2; and IV, n = 3). Neither initial nor late MRI signal changes after GKRS statistically correlated with surgical outcome. Clinical seizure outcome did not differ significantly with initial or late MRI changes after GKRS.

CONCLUSIONS

GKRS can be considered an alternative option when the patients with MTLE-HS who had recurrent or residual seizures after ATL refuse a second operation.

Minimally invasive techniques for epilepsy surgery: stereotactic radiosurgery and other technologies

Minimally invasive surgical techniques for the treatment of medically intractable epilepsy, which have been developed by neurosurgeons and epileptologists almost simultaneously with standard open epilepsy surgery, provide benefits in the traditional realms of safety and efficacy and the more recently appreciated realms of patient acceptance and costs. In this review, the authors discuss the shortcomings of the gold standard of open epilepsy surgery and summarize the techniques developed to provide minimally invasive alternatives. These minimally invasive techniques include stereotactic radiosurgery using the Gamma Knife, stereotactic radiofrequency thermocoagulation, laser-induced thermal therapy, and MRI-guided focused ultrasound ablation.

Radiosurgery for the treatment of dominant hemisphere periventricular heterotopia and intractable epilepsy in a series of three patients

Periventricular heterotopia (PVH) is a neuronal migration disorder characterized by masses of gray matter located along the lateral ventricles that commonly cause epilepsy. The benefit of surgical resection of the PVH has been demonstrated in case reports to date; however, the location of the PVH in the paratrigonal region of the lateral ventricles can present significant surgical challenges. Noninvasive modalities of ablating this epileptogenic focus must therefore be considered. We present a small series of three patients who underwent stereotactic radiosurgery (SRS) for inoperable unilateral dominant hemisphere PVHs in order to illustrate the potential benefits and risks of this treatment modality. A total dose of 37.5–65 Gy resulted in seizure freedom for at least 14 months at the time of their last follow-up, even in patients harboring a second independent epileptic focus. Whether intracranial electrode recording truly offers added value is therefore uncertain. The two patients who received higher radiation doses suffered from symptomatic radiation necrosis and associated cerebral edema, requiring further medical intervention, and persistent monocular visual loss in one patient. While a longer interval prior to re-treatment may have been attempted, neither patient demonstrated radiographic findings typically associated with seizure remission. Refractory epilepsy due to PVH may be successfully treated with radiation therapy; but further work is needed to define the optimal dosing parameters in order to lower toxicity to normal tissue.

Delayed complication after Gamma Knife surgery for mesial temporal lobe epilepsy

Object

Despite the controversy over the clinical significance of Gamma Knife surgery (GKS) for refractory mesial temporal lobe epilepsy (MTLE), the modality has attracted attention because it is less invasive than resection. The authors report long-term outcomes for 7 patients, focusing in particular on the long-term complications.

Methods

Between 1996 and 1999, 7 patients with MTLE underwent GKS. The 50% marginal dose covering the medial temporal structures was 18 Gy in 2 patients and 25 Gy in the remaining 5 patients.

Results

High-dose treatment abolished the seizures in 2 patients and significantly reduced them in 2 others. One patient in this group was lost to follow-up. However, 2 patients presented with symptomatic radiation necrosis (SRN) necessitating resection after 5 and 10 years. One patient who did not need necrotomy continued to show radiation necrosis on MRI after 10 years. One patient died of drowning while swimming in the sea 1 year after GKS, before seizures had disappeared completely.

Conclusions

High-dose treatment resulted in sufficient seizure control but carried a significant risk of SRN after several years. Excessive target volume was considered as a reason for delayed necrosis. Drawbacks such as a delay in seizure control and the risk of SRN should be considered when the clinical significance of this treatment is evaluated.

Radiosurgery for epilepsy: clinical experience and potential antiepileptic mechanisms

Stereotactic radiosurgery, well established in the noninvasive treatment of focal lesions that are otherwise difficult to access through open surgery, is an emerging technology in the treatment of focal epileptic lesions. Recent studies suggest that seizures from hypothalamic hamartomas and mesial temporal lobe epilepsy remit at clinically significant rates with radiosurgery, but large variations among different studies have raised questions about appropriate treatment protocols and mechanisms. Proposed anticonvulsant mechanisms include neuromodulatory effects or ischemic necrosis of epileptic tissue. An ongoing trial that directly compares efficacy, morbidities, and cost of radiosurgery versus open surgery for mesial temporal lobe epilepsy is underway.

Gamma knife radiosurgery for mesial temporal lobe epilepsy

Many patients with mesial temporal lobe epilepsy continue to have seizures despite medical therapy. For these patients, one recourse is surgical resection of the mesial temporal lobe, with its attendant risks. Noninvasive treatment with Gamma Knife radiosurgery is under active investigation as a possible alternative to open surgery. Accumulated evidence from multiple studies shows radiosurgery to be comparable in outcomes to surgical resection. A definitive randomized, controlled trial, the Radiosurgery or Open Surgery for Epilepsy (ROSE) trial, is currently underway, and further investigation of this promising treatment is crucial in our advancement of alternative therapies to treat refractory epilepsy.

Advances in the radiosurgical treatment of epilepsy

Radiosurgery is the precise application of focused radiation to a targeted volume area within the brain, which has been identified on MRI. With recent advances, radiosurgical treatment is now being evaluated as an alternative treatment to open resective surgery for intractable epilepsy. Recent prospective trials suggest that radiosurgery may be an effective and safe treatment for medically intractable epilepsy associated with mesial temporal sclerosis, cavernous malformations, and hypothalamic hamartomas.

Predictors of efficacy after stereotactic radiosurgery for medial temporal lobe epilepsy

BACKGROUND

Stereotactic radiosurgery (RS) is a promising treatment for intractable medial temporal lobe epilepsy (MTLE). However, the basis of its efficacy is not well understood.

METHODS

Thirty patients with MTLE were prospectively randomized to receive 20 or 24 Gy 50% isodose RS centered at the amygdala, 2 cm of the anterior hippocampus, and the parahippocampal gyrus. Posttreatment MRI was evaluated quantitatively for abnormal T2 hyperintensity and contrast enhancement, mass effect, and qualitatively for spectroscopic and diffusion changes. MRI findings were analyzed for potential association with radiation dose and seizure remission (Engel Ib or better outcome).

RESULTS

Despite highly standardized dose targeting, RS produced variable MRI alterations. In patients with multiple serial imaging, the appearance of vasogenic edema occurred approximately 9-12 months after RS and correlated with onset of seizure remission. Diffusion and spectroscopy-detected alterations were consistent with a mechanism of temporal lobe radiation injury mediated by local vascular insult and neuronal loss. The degree of these early alterations at the peak of radiographic response was dose-dependent and predicted long-term seizure remission in the third year of follow-up. Radiographic changes were not associated with neurocognitive impairments.

CONCLUSIONS

Temporal lobe stereotactic radiosurgery resulted in significant seizure reduction in a delayed fashion which appeared to be well-correlated with structural and biochemical alterations observed on neuroimaging. Early detected changes may offer prognostic information for guiding management.

Corpus callosotomy in children with intractable epilepsy using frameless stereotactic neuronavigation: 12-year experience at the Hospital for Sick Children in Toronto

OBJECT

Although corpus callosotomy has been used effectively since the late 1930s to treat severe, medically intractable seizure disorders, particularly atonic or drop-attack seizures, controversy remains as to when, how, and how much surgery should be performed. Intraoperative determination of the extent of callosotomy, the need to stage the procedure, and the side of the interhemispheric approach represent technical issues that remain debatable. The authors report the 12-year experience of the senior author as well as surgical outcomes with corpus callosotomy using a frameless stereotactic neuronavigation system (ISG View Wand and BrainLab).

METHODS

Thirteen consecutive children at The Hospital for Sick Children underwent single-stage corpus callosotomy for medically intractable seizures. The mean age was 10.3 years. Five children underwent partial callosotomy, and 8 underwent complete callosotomy. The side of operative approach to avoid large parasagittal bridging veins was determined by preoperative study of 3D MR imaging/MR venography reconstructed by the neuronavigation system. The extent of callosotomy was determined using intraoperative feedback from the neuronavigation system and postoperative MR imaging.

RESULTS

The extent of callosotomy determined by intraoperative neuronavigation and postoperative MR imaging correlated closely in all cases. There were no operative deaths. There was no significant postoperative morbidity related to venous infarction. Four of 5 patients in the partial callosotomy cohort and 7 of 8 patients in the complete callosotomy cohort showed significant improvement in seizure control.

CONCLUSIONS

The use of frameless stereotactic neuronavigation is a safe, effective, and important surgical adjunct in the planning and execution of successful corpus callosotomy in children with intractable epilepsy.

Long-term outcome of gamma-knife surgery in temporal lobe epilepsy

PURPOSE

Indication of gamma-knife surgery (GKS) in temporal lobe epilepsy (TLE) remains a matter of debate. Either positive or negative results have been reported in studies with a maximum follow-up of 24 months. No long-term data have been published yet.

METHODS

We collected data from 15 TLE patients who underwent GKS and whose follow-up was longer than 24 months. Localisation and extension of the epileptogenic zone (EZ) were assessed by SEEG in eight patients. Ten patients were presenting with mesial TLE (mTLE) while in the other five SEEG showed that the EZ was extending beyond mesio-temporal structures. GKS procedure was targeted to the EZ at a dose of 21.1+/-2.6Gy at the margin.

RESULTS

The mean duration of the follow-up was 60+/-22.3 months. At last follow-up, seven patients (46.7%) were free of disabling seizure. The last seizure following GKS occurred on average after a delay of 19.75+/-20.62 months. No patient suffered recurrent seizures after a long period free of disabling seizures. No significant prognostic predictor could be individualized in this population. However, 6 of the 10 patients with mTLE (60%) were seizure free whereas only 1 of the 5 (20%) whose EZ was more extended exhibited the same seizure outcome.

CONCLUSION

When a positive outcome is achieved, the risk of seizure recurrence remains low at long term. In patients with typical mTLE, long-term GKS results may be closed to those observed after conventional surgery. Conversely, this procedure should not be proposed to patients in whom SEEG results suggest that the EZ is not restricted to mesial temporal structures.

Treatment modality for intractable epilepsy in hypothalamic hamartomatous lesions

OBJECTIVE

Hypothalamic hamartomas (HHs) are often associated with early-onset gelastic seizures, thus configuring a well recognized and usually severe case of childhood epilepsy syndrome. We present a treatment modality for intractable epilepsy in hypothalamic hamartomatous lesions.

METHODS

This study presents 14 patients with medically refractory seizure associated with HHs treated between 1995 and 2005. The HHs were diagnosed on the basis of magnetic resonance imaging, except in the case of one patient in whom hamartoma was confirmed histologically. There were seven boys and seven girls in this study. The most frequent clinical presentations were seizures. To identify the epileptic focus, we performed comprehensive epilepsy investigations, including electroencephalographic recording using a depth electrode into the hamartoma.

RESULTS

To control the seizure, we performed surgical resection in one patient, gamma knife radiosurgery in four patients, and endoscopic disconnection in 11 patients. Seizure outcome was scored according to Engel's classification throughout a mean follow-up period of 27.4 months (range, 3-54 mo). Of the 11 patients who underwent endoscopic disconnection, six were seizure-free immediately after surgery. Two patients were already diagnosed as having an HH and underwent gamma knife radiosurgery, but seizure control was not achieved. Their gelastic seizure disappeared after endoscopic disconnection.

CONCLUSION

We confirmed that HHs are intrinsically epileptogenic. Therefore, we suggest that HH-related seizures may be controlled by blocking the seizure propagation from epileptogenic HHs through simple disconnection, regardless of the treatment modality, and the endoscopic disconnection of HHs is safer and more effective than other modalities.

[Radiosurgery for drug-resistant epilepsies: state of the art, results and perspectives]

BACKGROUND

There is growing interest in the use of radiosurgery in epilepsy. We analyzed our experience in this field in an attempt to define the potential of radiosurgery in epileptology.

MATERIAL AND METHODS

[corrected] Our local clinical experience (134 patients), accumulated over the last 15 years, mainly includes treatment of temporal lobe epilepsy without space-occupying lesions (59 patients), including 53 with pure MTLE, 61 cases of hypothalamic hamartoma, two cases of callosotomy, and 12 other types of epilepsy.

RESULTS

The analysis of our material, as well as other clinical and experimental data, suggest that the use of radiosurgery is beneficial only to patients in whom a strict preoperative definition of the extent of the epileptogenic zone (or network) has been achieved and strict rules of dose planning have been applied. As soon as these principles are not observed, the risk of treatment failure and/or side effects increases dramatically. Long-term outcome data are now available and published for MTLE but not yet for other types of epilepsy. Long-term safety and efficacy in MTLE are comparable to surgical resection but radiosurgery has the advantage of sparing verbal memory in patients operated by Gamma Knife (GK) on the dominant side. In small hamartomas, the efficacy is comparable to microsurgery but with a dramatic reduction in risk.

CONCLUSION

The vast amount of clinical materiel and long-term evaluation now support the use of GK surgery in small hypothalamic hamartomas and MTLE when the patient is at risk of verbal memory loss.

Radiosurgical posterior corpus callosotomy in a child with Lennox–Gastaut syndrome

The authors report the successful use of radiosurgery in a child for posterior corpus callosotomy; the early results are good and the patient has not suffered any morbid conditions. The relevant literature pertaining to the use of radiosurgery for treating epilepsy is reviewed. Details of the radiosurgical techniques and prescription dose used are presented, along with 1-year serial neuroimaging results.

Radiosurgery for epilepsy

Radiosurgery is an emerging therapeutic approach for the treatment of medically intractable epileptogenic foci. A favourable seizure outcome was first reported in studies of the effects of radiosurgery in the treatment of arteriovenous malformations and tumours. Radiosurgery has since been applied to the treatment of complex partial seizures with mesial-temporal-lobe onset. Nearly simultaneously, experimental evidence supporting the usefulness of radiosurgery to improve or abolish seizures has confirmed that stereotactic irradiation can preferentially affect epileptogenic versus normal cortex. Further work is clearly needed, but this technique might become an important approach in the management of mesial-temporal and extratemporal epilepsy, especially if refractory seizures arise from eloquent cortex or surgically challenging regions of brain.

Influence of ionizing radiation on the course of kindled epileptogenesis

Several clinical and experimental reports suggest that low-dose irradiation of an established epileptic focus can reduce the occurrence of spontaneous seizures. Conversely, some recent reports suggest that under some conditions low-dose irradiation may have disinhibitory effects on seizure expression. Here, we have investigated mechanistic aspects of this phenomenon in the kindling model of epilepsy by applying focal irradiation at various points during kindling development. Rats were kindled to stage 5 by afterdischarge-threshold electrostimulation of the left amygdala. Treatment groups were irradiated using a collimated X-ray beam (18 MV) either prior to kindling, at kindling stage 3, or at kindling stage 5, by exposure of the left amygdala to a single-fraction central-axis dose of 25 Gy. Generalized seizure thresholds (GSTs) were subsequently assayed at weekly intervals for 10 weeks and at monthly intervals for an additional 3 months, along with the severity of the evoked seizures. Irradiation produced no significant effects on seizure threshold, but did produce persistent changes in seizure severity which varied as a function of the timing of irradiation. Relative to sham irradiated controls, the occurrence of stage 6 seizures was significantly increased by irradiation prior to kindling, but was unaffected by irradiation at kindling stage 3, and significantly reduced by irradiation at kindling stage 5. Quantitative immunohistochemical assays for neuron and astrocyte densities within the amygdala and hippocampus revealed only subtle changes in neuronal density within the dentate granule cell layer. These results are discussed in relation to mechanisms of seizure- and radiation-induced plasticity.

FAILURE OF GAMMA KNIFE RADIOSURGERY FOR MESIAL TEMPORAL LOBE EPILEPSY: REPORT OF FIVE CASES

OBJECTIVE

We sought to determine the efficacy of gamma knife radiosurgery (GKRS) in controlling mesial temporal lobe epilepsy.

METHODS

From August 1999 to January 2001, five patients with drug-resistant mesial temporal lobe epilepsy due to hippocampal sclerosis underwent GKRS amygdalohippocampectomy. All of the patients underwent standard epilepsy preoperative evaluation at the comprehensive epilepsy center of the Cleveland Clinic Foundation. A marginal dose of 20 Gy to the 50% isodose line was delivered to the mesial temporal structures in all patients. Postoperative follow-up included serial neurological examinations, neuroimaging studies, and neuropsychological evaluations.

RESULTS

None of the patients were seizure-free after GKRS. Two patients died, 1 month and 1 year after the procedure, as a result of complications related to recurrent seizures. At 1 year, T2-weighted magnetic resonance imaging changes were noted in all three patients, which suggested radiational changes. None of the three surviving patients had any seizure reduction, so 18, 20, and 22 months after GKRS, they underwent temporal lobectomy, which resulted in complete seizure control in all patients.

CONCLUSION

GKRS at the 20-Gy dose level did not lead to seizure control in patients with mesial temporal lobe epilepsy due to hippocampal sclerosis.

Gamma Knife Surgery in Mesial Temporal Lobe Epilepsy: A Prospective Multicenter Study

PURPOSE

This article is the first prospective documentation of the efficacy and safety of gamma knife surgery (GKS) in the treatment of drug-resistant epilepsies of mesial temporal lobe origin.

METHODS

From July 1996 to March 2000, three European centers selected 21 patients with mesial temporal lobe epilepsy (MTLE) for a temporal lobectomy. The preoperative investigations included video-EEG with foramen ovale electrodes, magnetic resonance imaging, neuropsychological testing, and the ESI-55 quality-of-life questionnaire. In place of a cortectomy, radiosurgical treatment was performed by using the Leksell Gamma Knife (LGK) at a dose of 24 +/- 1 Gy at the margin. The target included the anterior parahippocampal cortex and the basal and lateral part of the amygdala and anterior hippocampus (head and body). One patient (a heavy smoker) died of a myocardial infarction. Twenty patients were available for prospective evaluation. A minimum 2-year follow-up period included clinical, neuropsychological, and radiologic evaluations.

RESULTS

At each 6-month follow-up evaluation, the frequency of seizures was significantly smaller than that at the previous visit. The median seizure frequency of 6.16 the month before treatment was reduced to 0.33 at 2 years after treatment. At 2 years, 65% of the patients (13 of 20) were seizure free. Five patients had transient side effects, including depression, headache, nausea, vomiting, and imbalance. There was no permanent neurological deficit reported except nine visual field deficits. No neuropsychological deterioration was observed 2 years after treatment. The quality of life was significantly better than that before surgery.

CONCLUSIONS

The safety and efficacy of the radiosurgical treatment of MTLEs appears good in this group of patient over short-to-middle term. Delay of the seizure cessation was the major disadvantage of GKS. A longer follow-up period is required for confirmation of these results.

Clinical outcome of epilepsy surgery

PURPOSE OF REVIEW

The outcome from current surgical methods of treating drug-resistant epilepsy will be considered, looking at changes in classical resective surgery and new methodology being introduced in the functional treatment of these patients.

RECENT FINDINGS

There is now class I evidence that temporal lobe surgery is effective. Sophisticated and appropriate magnetic resonance imaging sequences, together with an assessment of the electroclinical syndrome, allow patients to be assessed for resective surgery. The concept of 'surgically remediable syndromes' determines the type of procedure that is effective for particular patients. Technical advances such as neuronavigation techniques and intra-operative magnetic resonance imaging have improved the effectiveness of these procedures. Other techniques of disconnection, such as multiple subpial transection, and stimulation both indirectly using the vagus nerve and directly using various intracranial targets, are currently effective and have potential for future development.

SUMMARY

This review will demonstrate that current surgical techniques are safe and effective in relieving drug-resistant epilepsy.

Fractionated stereotactically guided radiotherapy of pharmacoresistant temporal lobe epilepsy

PURPOSE

This prospective study evaluated the efficacy of fractionated stereotactically guided radiotherapy (SRT) as a treatment of pharmacoresistant temporal lobe epilepsy.

PATIENTS AND METHODS

Inclusion criteria were patients aged between 17 and 65 years with unilateral temporal focus, without sufficient epilepsy control by antiepileptic drugs or neurosurgery. Two groups of 6 patients each were treated with 21 Gy (7 times 3 Gy) and 30 Gy (15 times 2 Gy). Study end points were change in seizure frequency, intensity, seizure length and neuropsychological parameters.

RESULTS

All patients experienced a marked reduction in seizure frequency. The mean reduction of seizures was 37% (range 9-77%, i.e. seizures reduced from a monthly mean number of 11.75 to 7.52) at 18 months following radiation treatment and 46% (23-94%, i.e. 0.2-23 seizures per month) during the whole follow-up time. Seizure length was reduced in 5 out of 11 patients and intensity of seizures in 7 out of 11 patients.

CONCLUSION

Radiotherapy was identified as a safe and effective treatment for pharmacoresistant epilepsy since a good reduction of seizure frequency during longer follow-up was observed. SRT means an appropriate alternative for patients with contraindication against neurosurgery or insufficient seizure reduction after neurosurgery.