Surgical outcome in occipital lobe epilepsy: implications for pathophysiology

Circumscribing Laser Cuts Attenuate Seizure Propagation in a Mouse Model of Focal Epilepsy

In partial onset epilepsy, seizures arise focally in the brain and often propagate. Patients frequently become refractory to medical management, leaving neurosurgery, which can cause neurologic deficits, as a primary treatment. In the cortex, focal seizures spread through horizontal connections in layers II/III, suggesting that severing these connections can block seizures while preserving function. Focal neocortical epilepsy is induced in mice, sub-surface cuts are created surrounding the seizure focus using tightly-focused femtosecond laser pulses, and electrophysiological recordings are acquired at multiple locations for 3-12 months. Cuts reduced seizure frequency in most animals by 87%, and only 5% of remaining seizures propagated to the distant electrodes, compared to 80% in control animals. These cuts produced a modest decrease in cortical blood flow that recovered and left a ≈20-µm wide scar with minimal collateral damage. When placed over the motor cortex, cuts do not cause notable deficits in a skilled reaching task, suggesting they hold promise as a novel neurosurgical approach for intractable focal cortical epilepsy.

Protocol of a prospective multicenter randomized controlled trial of robot-assisted stereotactic lesioning in the treatment of focal drug-resistant epilepsy

BACKGROUND

This protocol describes the design of a multicenter randomized controlled trial of robot-assisted stereotactic lesioning versus epileptogenic foci resection. Typical causes of focal epilepsy include hippocampal sclerosis and focal cortical dysplasia. These patients usually present with drug resistance and require surgical treatment. Although epileptogenic foci resection is still the most commonly used treatment for such focal epilepsy, there is increasing evidence that epileptogenic focus resection may lead to neurological impairment. The treatment of epilepsy with a robot-assisted stereotactic lesioning mainly includes two new minimally invasive surgical methods: radiofrequency thermocoagulation (RF-TC) and laser interstitial thermal therapy (LITT). Seizure-free is less likely to be achieved by these two procedures, but neurologic preservation is better. In this study, we aimed to compare the safety and efficacy of RF-TC, LITT, and epileptogenic foci resection for focal drug-resistant epilepsy.

METHODS

This is a multicenter, three-arm, randomized controlled clinical trial. The study will include patients older than 3 years of age with epilepsy who have had medically refractory seizures for at least 2 years and are eligible for surgical treatment with an epileptogenic focus as determined by multidisciplinary evaluation prior to randomization. The primary outcome measure is seizure outcome (quantified by seizure remission rate) at 3-month, 6-month, and 1-year follow-up after treatment. Postoperative neurologic impairment, spectrum distribution change of video electroencephalogram, quality of life, and medical costs will also be assessed as secondary outcomes.

TRIAL REGISTRATION

Chinese Clinical Trials Registry ChiCTR2200060974. Registered on June 14, 2022. The status of the trial is recruiting, and the estimated study completion date is December 31, 2024.

Glymphatic system dysfunction in patients with occipital lobe epilepsy

BACKGROUND AND PURPOSE

We aimed to investigate the glymphatic system function in patients with occipital lobe epilepsy (OLE) and healthy controls using diffusion tensor image analysis along the perivascular space (DTI-ALPS) index.

METHODS

We retrospectively included 23 patients with OLE and 30 healthy controls. The participants underwent brain MRI, which was normal, and diffusion tensor imaging. We used the DSI Studio for data preprocessing, obtained the fiber orientation and diffusivities, and calculated the DTI-ALPS index from the diffusivity values associated with the projection and association fibers in the left hemisphere.

RESULTS

There were no differences in mean age (31.6 years [range: 13-58] vs. 31.3 years [range: 20-57], p = .912) and male sex ratio (10/23 [43.5%] vs. 15/30 [50.0%]) between the groups. Compared to healthy controls, the diffusivities in patients with OLE were higher along the Y-axis in the projection fiber and along the Z-axis in the association fiber and lower along the Y-axis in the association fiber. The DTI-ALPS index in patients with OLE was lower than that in the healthy controls (1.421 ± 0.171 vs. 1.667 ± 0.271, p < .001, 95% confidence interval of difference = 0.117-0.376, Test statistic t = 3.823). We found no association between the DTI-ALPS index and clinical characteristics in OLE.

CONCLUSION

The DTI-ALPS index in patients with OLE was significantly lower than that in healthy controls, suggesting glymphatic system dysfunction in OLE. The DTI-ALPS index could help assess the glymphatic system function in patients with epilepsy.

Seizure onset zone classification based on imbalanced iEEG with data augmentation

Objective. Identifying the seizure onset zone (SOZ) in patients with focal epilepsy is the critical information required for surgery. However, collecting this information is challenging, time-consuming, and subjective. Some machine learning methods reduce the workload of clinical experts in intracranial electroencephalogram (iEEG) visual diagnosis but face significant challenges because interictal iEEG clinical data often suffer from a significant class imbalance. We aim to generate synthetic data for the minority class.Approach. To make the clinically imbalanced data suitable for machine learning, we introduce an EEG augmentation method (EEGAug). The EEGAug method randomly selects several samples from the minority class and transforms them into the frequency domain. Then, different frequency bands from different samples are used to compose new data. Finally, a synthetic sample is generated after converting the new data back to the time domain.Main results. The imbalanced clinical iEEG data can be balanced and applied to machine learning models using the method. A one-dimensional convolutional neural network model is used to classify the SOZ and non-SOZ data. We compare the EEGAug method with other data augmentation methods and another method of class-balanced focal loss function, which is also used for solving the data imbalance problem by adjusting the weights between the minority and majority classes. The results show that the EEGAug method performs best in most data.Significance. Data imbalance is a widespread clinical problem. The EEGAug method can flexibly generate synthetic data for the minority class, yielding synthetic and raw data with a high distribution similarity. By using the EEGAug method, clinical data can be used in machine learning models.

An Unusual Presentation of Vivid Hallucinations

Visual hallucinations may present secondary to neurologic, psychologic, or physiologic disturbances. Certain features and characteristics of visual hallucination are often attributed to various brain regions; however, with a broad list of causes and multifaceted pathophysiology, it is often hard to accurately localize. Overlapping clinical presentations may be due to the pathology of brain interconnections, rather than isolated brain regions themselves. In this study, we discuss a case of isolated, complex visual hallucinations secondary to occipital seizures in the radiologic absence of an ischemic injury. We propose that a network-based localizing lesion is responsible for this unconventional presentation.

Resection of bilateral occipital lobe lesions during a single operation as a treatment for bilateral occipital lobe epilepsy

BACKGROUND

Neurosurgical treatment of severe bilateral occipital lobe epilepsy usually involves two operations several mos apart.

AIM

To evaluate surgical resection of bilateral occipital lobe lesions during a single operation as a treatment for bilateral occipital lobe epilepsy.

METHODS

This retrospective case series included patients with drug-refractory bilateral occipital lobe epilepsy treated surgically between March 2006 and November 2015.

RESULTS

Preoperative evaluation included scalp video-electroencephalography (EEG), magnetic resonance imaging, and PET-CT. During surgery (bilateral occipital craniotomy), epileptic foci and important functional areas were identified by EEG (intracranial cortical electrodes) and cortical functional mapping, respectively. Patients were followed up for at least 5 years to evaluate treatment outcome (Engel grade) and visual function. The 20 patients (12 males) were aged 4-30 years (median age, 12 years). Time since onset was 3-20 years (median, 8 years), and episode frequency was 4-270/mo (median, 15/mo). Common manifestations were elementary visual hallucinations (65.0%), flashing lights (30.0%), blurred vision (20.0%) and visual field defects (20.0%). Most patients were free of disabling seizures (Engel grade I) postoperatively (18/20, 90.0%) and at 1 year (18/20, 90.0%), 3 years (17/20, 85.0%) and ≥ 5 years (17/20, 85.0%). No patients were classified Engel grade IV (no worthwhile improvement). After surgery, there was no change in visual function in 13/20 (65.0%), development of a new visual field defect in 3/20 (15.0%), and worsening of a preexisting defect in 4/20 (20.0%).

CONCLUSION

Resection of bilateral occipital lobe lesions during a single operation may be applicable in bilateral occipital lobe epilepsy.

POSTERIOR CORTEX SEIZURES - PEDIATRIC CHALLENGES

Posterior cortex seizures have a complex semiologic presentation that is especially challenging in the pediatric population. Therefore, using clinical presentation in localizing ictal involvement is not sufficient in children, thus making this type of epilepsy quite under-recognized. As most of the ictal symptoms are subjective and could well be overshadowed by symptoms arising from adjacent cortices, primarily temporal and central ones, it is necessary not to overlook this large source of pharmacoresistant epilepsies. The parietal lobe as part of an extensive synaptic network is a great imitator, thus quite often producing inaccurate localization readings on scalp electroencephalography (EEG) due to very scattered interictal discharges and uninformative ictal recordings. Using direct cortical recordings in delineating the epileptogenic zone is helpful in some cases but even highly experienced epileptologists may erroneously interpret some features as arising from other localizations, especially the frontal lobe. Epilepsy surgery from the posterior quadrant is still quite rare and relatively unsuccessful, especially in non-lesional epilepsies due to elaborate mechanisms of connectivity, misleading semiology, and non-localizing EEG recordings, possibly due to insufficiency of parietal cortex synchronicity. Applying the aforementioned to the pediatric age makes it perhaps the most difficult challenge for a pediatric epileptologist.

Ictal blinking in focal seizures: Insights from SEEG recordings

PURPOSE

Ictal blinking may be observed in various forms of epilepsies. In the context of presurgical assessment of drug-resistant focal epilepsies, its semiological value is poorly understood. Our aims were to determine the prevalence and localizing value of ictal blinking.

METHODS

We reviewed our cohort of more than 300 patients explored by SEEG, searching for ictal blinking. We defined seizure onset zone (SOZ) using visual analysis complemented by a quantified method (epileptogenicity index). We analysed the features of ictal blinking and the associated signs. We tested for statistically significant associations with the underlying SOZ.

RESULTS

We found that about 8% of our patients exhibited ictal blinking, mostly bilateral. Ictal blinking was seen mostly in four types of SOZ: occipital, occipito-temporal, temporal mesial, and insulo-opercular. It was significantly over-represented in occipito-temporal and occipital SOZ. Eye blinking was fastest in insulo-opercular SOZ and slowest in temporal mesial SOZ. Nystagmus and tonic eye deviation were associated with SOZ involving the occipital lobe.

CONCLUSION

Ictal blinking is not uncommon in the population of patients with drug-resistant focal epilepsies. It is mostly associated with four types of SOZ: occipital, occipito-temporal, temporal mesial, and insulo-opercular. Some features of ictal blinking, as well as the analysis of the associated signs, allow to orient clinical hypotheses toward some specific SOZ.

Awake perimetry testing for occipital epilepsy surgery

With the patient awake during surgery, the authors used a simple technique to determine which part of a patient's brain was essential for vision. This technique allows the surgeon to remove as much as the seizure-producing brain as possible by avoiding the areas that are critical for vision.

Disconnection Surgery for Intractable Epilepsy with a Structural Abnormality in the Medial Posterior Cortex

BACKGROUND

The lesionectomy is a general surgical procedure for treating focal epilepsy resulting from a structural abnormality, but a favorable outcome cannot be achieved in some patients, especially patients whose symptomatogenic zone is located in remote regions. Herein we propose the surgical disconnection of the seizure propagation pathway, which consists of short and long associating fibers linking the epileptogenic zone to the remote symptomatogenic zone, as an effective method of achieving favorable seizure outcomes in patients with posterior cortex epilepsy.

METHODS

Three patients with intractable epilepsy showing a structural abnormality in the medial posterior cortex participated in this study. Their habitual seizures were complex partial seizures stemming from remote symptomatogenic zones. Seizure propagation-related fibers were assumed by non-invasive examination and semiology.

RESULTS

Cingulum and superior/inferior longitudinal fasciculus were considered to form main seizure propagation pathway. Based on the preoperative assumption and the intraoperative intracranial electroencephalogram findings, a lesionectomy and corticectomy were performed for 2 patients while a clusterectomy and corticectomy were performed for the remaining patient. The resection area was extended in the direction of the association fibers to disconnect the remote symptomatogenic zone completely from the epileptogenic zone. Engel class I was achieved in all the patients.

CONCLUSION

The current study suggested that assuming the presence of association fibers was an important factor for achieving a favorable outcome in the surgical treatment of posterior cortex epilepsy. Though further study is required, disconnection surgery is recommended as a treatment option for cases in which the epileptogenic zone is located in an eloquent area.

Seizure Outcomes in Occipital Lobe and Posterior Quadrant Epilepsy Surgery: A Systematic Review and Meta-Analysis

BACKGROUND

Occipital lobe epilepsy (OLE) is an uncommon but debilitating focal epilepsy syndrome with seizures often refractory to medical management. While surgical resection has proven a viable treatment, previous studies examining postoperative seizure freedom rates are limited by small sample size and patient heterogeneity, thus exhibiting significant variability in their results.

OBJECTIVE

To review the medical literature on OLE so as to investigate rates and predictors of both seizure freedom and visual outcomes following surgery.

METHODS

We reviewed manuscripts exploring surgical resection for drug-resistant OLE published between January 1990 and June 2015 on PubMed. Seizure freedom rates were analyzed and potential predictors were evaluated with separate meta-analyses. Postoperative visual outcomes were also examined.

RESULTS

We identified 27 case series comprising 584 patients with greater than 1 yr of follow-up. Postoperative seizure freedom (Engel class I outcome) was observed in 65% of patients, and was significantly predicted by age less than 18 yr (odds ratio [OR] 1.54, 95% confidence interval [CI] 1.13-2.18), focal lesion on pathological analysis (OR 2.08, 95% CI 1.58-2.89), and abnormal preoperative magnetic resonance imaging (OR 3.24, 95% 2.03-6.55). Of these patients, 175 also had visual outcomes reported with 57% demonstrating some degree of visual decline following surgery. We did not find any relationship between postoperative visual and seizure outcomes.

CONCLUSION

Surgical resection for OLE is associated with favorable outcomes with nearly two-thirds of patients achieving postoperative seizure freedom. However, patients must be counseled regarding the risk of visual decline following surgery.

Factors affecting seizure outcome after epilepsy surgery: an observational series

IMPORTANCE

Surgical treatment can bring seizure remission in people with focal epilepsy but requires careful selection of candidates.

OBJECTIVES

To determine which preoperative factors are associated with postoperative seizure outcome.

DESIGN

We audited seizure outcome of 693 adults who had resective epilepsy surgery between 1990 and 2010 and used survival analysis to detect preoperatively identifiable risk factors of poor seizure outcome.

RESULTS

Seven factors were significantly associated with increased probability of recurrence of seizures with impaired awareness postsurgery: MRI findings (eg, HR adjusted for other variables in the model 2.5; 95% CI 1.6 to 3.8 for normal MRI compared with hippocampal sclerosis), a history of secondarily generalised convulsive seizures (2.3; 95% CI 1.7 to 3.0 for these seizures in the previous year vs never), psychiatric history (1.3; 95% CI 1.1 to 1.7), learning disability (1.8; 95% CI 1.2 to 2.6) and extratemporal (vs temporal) surgery (1.4; 95% CI 1.02, 2.04). People with an older onset of epilepsy had a higher probability of seizure recurrence (1.01; 95% CI 1.00, 1.02) as did those who had used more antiepileptic drugs (1.05; 95% CI 1.01 to 1.09). Combinations of variables associated with seizure recurrence gave overall low probabilities of 5-year seizure freedom (eg, a normal MRI and convulsive seizures in the previous year has a probability of seizure freedom at 5 years of approximately 0.19).

CONCLUSIONS AND RELEVANCE

Readily identified clinical features and investigations are associated with reduced probability of good outcome and need consideration when planning presurgical evaluation.

Relationship between cortical resection and visual function after occipital lobe epilepsy surgery

OBJECTIVE In this study, the authors investigated long-term clinical and visual outcomes of patients after occipital lobe epilepsy (OLE) surgery and analyzed the relationship between visual cortical resection and visual function after OLE surgery. METHODS A total of 42 consecutive patients who were diagnosed with OLE and underwent occipital lobe resection between June 1995 and November 2013 were included. Clinical, radiological, and histopathological data were reviewed retrospectively. Seizure outcomes were categorized according to the Engel classification. Visual function after surgery was assessed using the National Eye Institute Visual Functioning Questionnaire 25. The relationship between the resected area of the visual cortex and visual function was demonstrated by multivariate linear regression models. RESULTS After a mean follow-up period of 102.2 months, 27 (64.3%) patients were seizure free, and 6 (14.3%) patients had an Engel Class II outcome. Nineteen (57.6%) of 33 patients had a normal visual field or quadrantanopia after surgery (normal and quadrantanopia groups). Patients in the normal and quadrantanopia groups had better vision-related quality of life than those in the hemianopsia group. The resection of lateral occipital areas 1 and 2 of the occipital lobe was significantly associated with difficulties in general vision, peripheral vision, and vision-specific roles. In addition, the resection of intraparietal sulcus 3 or 4 was significantly associated with decreased social functioning. CONCLUSIONS The authors found a favorable seizure control rate (Engel Class I or II) of 78.6%, and 57.6% of the subjects had good visual function (normal vision or quadrantanopia) after OLE surgery. Lateral occipital cortical resection had a significant effect on visual function despite preservation of the visual field.

Improvement of visual field defects after focal resection for occipital lobe epilepsy: case report

Improvement of visual field defects after surgical treatment for occipital lobe epilepsy is rare. Here, the authors report on a 24-year-old man with a 15-year history of refractory epilepsy that developed after he had undergone an occipital craniotomy to remove a cerebellar astrocytoma at the age of 4. His seizures started with an elementary visual aura, followed by secondary generalized tonic-clonic convulsion. Perimetry revealed left-sided incomplete hemianopia, and MRI showed an old contusion in the right occipital lobe. After evaluation with ictal video-electroencephalography, electrocorticography, and mapping of the visual cortex with subdural electrodes, the patient underwent resection of the scarred tissue, including the epileptic focus at the occipital lobe. After surgery, he became seizure free and his visual field defect improved gradually. In addition, postoperative ¹²³I-iomazenil (IMZ) SPECT showed partly normalized IMZ uptake in the visual cortex. This case is a practical example suggesting that neurological deficits attributable to the functional deficit zone can be remedied by successful focal resection.

Adult Focal Epilepsies

PURPOSE OF REVIEW

Focal epilepsy is the most common type of epilepsy in adulthood. This article discusses the seizure symptomatology, EEG findings, and imaging findings of the various forms of focal epilepsy. The majority of the article focuses on temporal and frontal lobe epilepsy as these represent the majority of focal epilepsies.

RECENT FINDINGS

While significant overlap exists in the clinical symptomatology of the focal epilepsies, detailed seizure descriptions can often provide useful clinical evidence to help establish an accurate diagnosis. EEG and MRI continue to serve as the main diagnostic tools for the diagnosis of focal epilepsy.

SUMMARY

The various forms of focal epilepsy generate seizure presentations that are dependent on the anatomic structures that are involved in the seizure. By understanding the symptoms typically generated in each region of the brain, a better understanding of the possible seizure localizations can be made. Most forms of epilepsy have clear changes on EEG that permit accurate localization, but several pitfalls exist, which are discussed in this article. Imaging has revolutionized our ability to accurately identify lesions associated with epilepsy and increased our ability to localize seizures in the brain.

Occipital and occipital "plus" epilepsies: A study of involved epileptogenic networks through SEEG quantification

Compared with temporal or frontal lobe epilepsies, the occipital lobe epilepsies (OLE) remain poorly characterized. In this study, we aimed at classifying the ictal networks involving OLE and investigated clinical features of the OLE network subtypes. We studied 194 seizures from 29 consecutive patients presenting with OLE and investigated by stereoelectroencephalography (SEEG). Epileptogenicity of occipital and extraoccipital regions was quantified according to the 'epileptogenicity index' (EI) method. We found that 79% of patients showed widespread epileptogenic zone organization, involving parietal or temporal regions in addition to the occipital lobe. Two main groups of epileptogenic zone organization within occipital lobe seizures were identified: a pure occipital group and an occipital "plus" group, the latter including two further subgroups, occipitotemporal and occipitoparietal. In 29% of patients, the epileptogenic zone was found to have a bilateral organization. The most epileptogenic structure was the fusiform gyrus (mean EI: 0.53). Surgery was proposed in 18/29 patients, leading to seizure freedom in 55% (Engel Class I). Results suggest that, in patient candidates for surgery, the majority of cases are characterized by complex organization of the EZ, corresponding to the occipital plus group.

A comparison of occipital and temporal lobe epilepsies

PURPOSE

Differentiating between occipital lobe epilepsy (OLE) and temporal lobe epilepsy (TLE) is often challenging. This retrospective case-control study compares OLE to TLE and explores markers that suggest the diagnosis of OLE.

METHODS

We queried the Jefferson Epilepsy Center surgery database for patients who underwent a resection that involved the occipital lobe. For each patient with OLE, three sequential case-control patients with TLE were matched. Demographic characteristics, symptoms, electrophysiological findings, imaging findings, and surgical outcome were compared.

RESULTS

Nineteen patients with OLE and 57 patients with TLE were included in the study. Visual symptoms were unique to patients with OLE (8/19) and were not reported by patients with TLE (P < 0.0001). Occipital interictal spikes (IIS) were found only in one-third of the patients with OLE (6/19) and in no patients with TLE (P < 0.0001). IIS in the posterior temporal lobe were found in five of 19 patients with OLE vs one of 57 patients with TLE (P = 0.003). IIS involved more than one lobe of the brain in most patients with OLE (11/19) but only in nine of 57 the TLE group. (P = 0.0003) Multilobar resection was needed in most patients with OLE (15/19), typically including the temporal lobe, but in only one of the patients with TLE (P < 0.0001).

CONCLUSION

Occipital lobe epilepsy is difficult to identify and may masquerade as temporal lobe epilepsy. Visual symptoms and occipital findings in the EEG suggest the diagnosis of OLE, but absence of these features, does not exclude the diagnosis. When posterior temporal EEG findings or multilobar involvement occurs, the diagnosis of OLE should be considered.

The Classical Pathways of Occipital Lobe Epileptic Propagation Revised in the Light of White Matter Dissection

The clinical evidences of variable epileptic propagation in occipital lobe epilepsy (OLE) have been demonstrated by several studies. However the exact localization of the epileptic focus sometimes represents a problem because of the rapid propagation to frontal, parietal, or temporal regions. Each white matter pathway close to the supposed initial focus can lead the propagation towards a specific direction, explaining the variable semiology of these rare epilepsy syndromes. Some new insights in occipital white matter anatomy are herein described by means of white matter dissection and compared to the classical epileptic patterns, mostly based on the central position of the primary visual cortex. The dissections showed a complex white matter architecture composed by vertical and longitudinal bundles, which are closely interconnected and segregated and are able to support specific high order functions with parallel bidirectional propagation of the electric signal. The same sublobar lesions may hyperactivate different white matter bundles reemphasizing the importance of the ictal semiology as a specific clinical demonstration of the subcortical networks recruited. Merging semiology, white matter anatomy, and electrophysiology may lead us to a better understanding of these complex syndromes and tailored therapeutic options based on individual white matter connectivity.

Intractable occipital lobe epilepsy: clinical characteristics, surgical treatment, and a systematic review of the literature

PURPOSE

We reported our experience in the surgical treatment of a relatively large cohort of patients with occipital lobe epilepsy (OLE). We also carried out a systematic review of the literature on OLE.

METHODS

Thirty-five consecutive patients who underwent occipital resection for epilepsy were included. Diagnoses were made following presurgical evaluations, including magnetic resonance imaging (MRI), fluorodeoxyglucose-positron emission tomography (FDG-PET), scalp video-electroencephalogram (EEG) monitoring, and intracranial EEG monitoring. At last follow-up, seizure outcome was classified using the Engel classification scheme.

RESULTS

Twenty-five of 35 patients experienced/had experienced ≥1 type of aura before the seizure. Invasive recordings were used to define the epileptogenic area in 30 of 35 patients (85.7 %). All patients underwent occipital lesionectomies or topectomies. Histopathology revealed: cortical dysplasias, gliosis, dysembryoplastic neuroepithelial tumor, ganglioglioma, and tuberous sclerosis. After a mean follow-up of 44 months, 25 patients (71.4 %) were seizure free (Engel class I), 3 (8.6 %) rarely had seizures (Engel class II), 5 (14.3 %) improved more than 75 % (Engel class III), and 2 (5.7 %) had no significant improvement (Engel class IV). Preoperatively, 12 of 33 patients (36.4 %) had visual field deficits. Postoperatively, 25 patients (75.8 %) had new or aggravated visual field deficits.

CONCLUSIONS

The management of OLE has been aided greatly by the availability of high-resolution diagnosis. Postoperative visual field deficits occur in a significant proportion of patients. Comprehensive intracranial EEG coverage of all occipital surfaces helps to define the epileptogenic area and preserve visual function, especially in cases of focal cortical dysplasia undetectable by MRI.

The role of resting state networks in focal neocortical seizures

Objective

The role of resting state functional networks in epilepsy is incompletely understood. While some pathologic diagnoses have been shown to have maintained but altered resting state connectivity, others have implicated resting state connectivity in disease progression. However little is known about how these resting state networks influence the behavior of a focal neocortical seizure.

Methods

Using data taken from invasively monitored patients with intractable focal neocortical epilepsy, we evaluated network connectivity (as determined by oscillatory covariance of the slow cortical potential (<0.5 Hz)) as it relates to neocortical seizure foci both in the interictal and ictal states.

Results

Similar to what has been shown in the past for sleep and anesthesia, electophysiologic resting state networks that are defined by this slow cortical potential covariance maintain their topographic correlation structure throughout an ictal event. Moreover, in the context of focal epilepsy in which the seizure has a specific site of onset, seizure propagation is not chaotic or random. Rather, the seizure (reflected by an elevation of high frequency power) preferentially propagates along the network that contains the seizure onset zone.

Significance

Taken together, these findings further undergird the fundamental role of resting state networks, provide novel insights into the network-influenced behavior of seizures, and potentially identify additional targets for surgical disconnection including informing the location for the completion of multiple subpial transections (MSPTs).

Surgery for drug-resistant focal epilepsy

During the colloquium on drug-resistant epilepsy (DRE) at National Institute of Mental Health and Neurosciences (NIMHANS), Bangalore on August 16-18, 2013, a number of presentations were made on the surgically remediable lesional epilepsy syndromes, presurgical evaluation, surgical techniques, neuropathology of drug resistance focal epilepsy and surgical outcome. This pictorial essay with the illustrative case examples provides an overview of the various surgical techniques for the management of drug-resistant focal epilepsy.

Video electroencephalogram telemetry in temporal lobe epilepsy

Temporal lobe epilepsy (TLE) is the most commonly encountered medically refractory epilepsy. It is also the substrate of refractory epilepsy that gives the most gratifying results in any epilepsy surgery program, with a minimum use of resources. Correlation of clinical behavior and the ictal patterns during ictal behavior is mandatory for success at epilepsy surgery. Video electroencephalogram (EEG) telemetry achieves this goal and hence plays a pivotal role in pre-surgical assessment. The role of telemetry is continuously evolving with the advent of digital EEG technology, of high-resolution volumetric magnetic resonance imaging and other functional imaging techniques. Most of surgical selection in patients with TLE can be done with a scalp video EEG monitoring. However, the limitations of the scalp EEG technique demand invasive recordings in a selected group of TLE patients. This subset of the patients can be a challenge to the epileptologist.

The cognitive profile of occipital lobe epilepsy and the selective association of left temporal lobe hypometabolism with verbal memory impairment

We investigated the cognitive profile of structural occipital lobe epilepsy (OLE) and whether verbal memory impairment is selectively associated with left temporal lobe hypometabolism on [18F]-fluorodeoxyglucose positron emission tomography (FDG-PET). Nine patients with OLE, ages 8-29 years, completed presurgical neuropsychological assessment. Composite measures were calculated for intelligence quotient (IQ), speed, attention, verbal memory, nonverbal memory, and executive functioning. In addition, the Wisconsin Card Sorting Test (WCST) was used as a specific measure of frontal lobe functioning. Presurgical FDG-PET was analyzed with statistical parametric mapping in 8 patients relative to 16 healthy volunteers. Mild impairments were evident for IQ, speed, attention, and executive functioning. Four patients demonstrated moderate or severe verbal memory impairment. Temporal lobe hypometabolism was found in seven of eight patients. Poorer verbal memory was associated with left temporal lobe hypometabolism (p = 0.002), which was stronger (p = 0.03 and p = 0.005, respectively) than the association of left temporal lobe hypometabolism with executive functioning or with performance on the WCST. OLE is associated with widespread cognitive comorbidity, suggesting cortical dysfunction beyond the occipital lobe. Verbal memory impairment is selectively associated with left temporal lobe hypometabolism in OLE, supporting a link between neuropsychological dysfunction and remote hypometabolism in focal epilepsy.

Long-term outcome and predictors of resective surgery prognosis in patients with refractory extratemporal epilepsy

PURPOSE

We analyzed the long-term postoperative outcome and possible predictive factors of the outcome in surgically treated patients with refractory extratemporal epilepsy.

METHODS

We retrospectively analyzed 73 patients who had undergone resective surgery at the Epilepsy Center Brno between 1995 and 2010 and who had reached at least 1 year outcome after the surgery. The average age at surgery was 28.3±11.4 years. Magnetic resonance imaging (MRI) did not reveal any lesion in 24 patients (32.9%). Surgical outcome was assessed annually using Engel's modified classification until 5 years after surgery and at the latest follow-up visit.

RESULTS

Following the surgery, Engel Class I outcome was found in 52.1% of patients after 1 year, in 55.0% after 5 years, and in 50.7% at the last follow-up visit (average 6.15±3.84 years). Of the patients who reached the 5-year follow-up visit (average of the last follow-up 9.23 years), 37.5% were classified as Engel IA at each follow-up visit. Tumorous etiology and lesions seen in preoperative MRI were associated with significantly better outcome (p=0.035; p<0.01). Postoperatively, 9.6% patients had permanent neurological deficits.

CONCLUSION

Surgical treatment of refractory extratemporal epilepsy is an effective procedure. The presence of a visible MRI-detected lesion and tumorous etiology is associated with significantly better outcome than the absence of MRI-detected lesion or other etiology.

Occipital lobe seizures and epilepsies

Occipital lobe epilepsies (OLEs) manifest with occipital seizures from an epileptic focus within the occipital lobes. Ictal clinical symptoms are mainly visual and oculomotor. Elementary visual hallucinations are common and characteristic. Postictal headache occurs in more than half of patients (epilepsy-migraine sequence). Electroencephalography (EEG) is of significant diagnostic value, but certain limitations should be recognized. Occipital spikes and/or occipital paroxysms either spontaneous or photically induced are the main interictal EEG abnormalities in idiopathic OLE. However, occipital epileptiform abnormalities may also occur without clinical relationship to seizures particularly in children. In cryptogenic/symptomatic OLE, unilateral posterior EEG slowing is more common than occipital spikes. In neurosurgical series of symptomatic OLE, interictal EEG abnormalities are rarely strictly occipital. The most common localization is in the posterior temporal regions and less than one-fifth show occipital spikes. In photosensitive OLE, intermittent photic stimulation elicits (1) spikes/polyspikes confined in the occipital regions or (2) generalized spikes/polyspikes with posterior emphasis. In ictal EEG, a well-localized unifocal rhythmic ictal discharge during occipital seizures is infrequent. A bioccipital field spread to the temporal regions is common. Frequency, severity, and response to treatment vary considerably from good to intractable and progressive mainly depending on underlying causes.

Role of electroencephalography in presurgical evaluation of temporal lobe epilepsy

Surgery remains a therapeutic option for patients with medically refractory epilepsy. Comprehensive presurgical evaluation includes electroencephalography (EEG) and video EEG in identifying patients who are likely to benefit from surgery. Here, we discuss in detail the utility of EEG in presurgical evaluation of patients with temporal lobe epilepsy along with illustrative cases.

Posterior resection for childhood lesional epilepsy: neuropsychological evolution

The aim of this study was to provide information on the neuropsychological evolution of children with symptomatic epilepsy who have undergone surgical resection of posterior (occipitoparietal) lesions. Twelve children with epilepsy with parietal and/or occipital lesions were enrolled in the study and followed after surgical resection: full clinical and epileptic examinations were performed before and after surgery, as was a neuropsychological study of both general and specific cognitive abilities. Epilepsy evolution was generally good (Engel classification IA in nine cases) with persistent selective neurological impairments (eye field defects, sensory unilateral spatial neglect) in some cases, consistent with the lesion site. Neuropsychological defects before surgery in the absence of refractory epilepsy were minimal with a normal global cognitive competence; yet, the relatively low performance scores with some impairment of specific cognitive skills were strictly correlated with defects in visual perceptive skills in both right- and left-sided lesions. Surgery seems to have improved performance abilities, whereas other abnormal specific skills did not change with the exception of working memory that in some cases was defective before surgery and normalized after lesion removal. Our study in this particular cohort of children with epileptogenic occipitoparietal lesions thus confirmed a trend toward a benign epileptic and neurodevelopmental outcome after surgical resection of the lesion.

Efficacy of vagus nerve stimulation for refractory epilepsy among patient subgroups: a re-analysis using the Engel classification

Optimal candidates for VNS as a treatment for refractory epilepsy have not been identified. In this retrospective two-center study, we used the Engel classification for evaluating seizure outcome, and tried to identify predictive factors for outcome by means of subgroup analysis. The medical records of patients who have been treated with VNS for at least one year at Dartmouth-Hitchcock Medical Center and Ghent University Hospital were evaluated. Seizure frequency outcome was assessed using the Engel classification for the study population as a whole, and for patient subgroups with regard to mental functioning, seizure type, predisposing factors for developing epilepsy, age at time of VNS implantation and epilepsy duration. 189 patients (102M/87F) were included in the study (mean FU: 41 months). 6% had a class I outcome (seizure-free), 13% a class II outcome (almost seizure-free), 49% a class III outcome (worthwhile improvement) and 32% had a class IV outcome (no improvement). When patients were divided into specific subgroups, a statistically significant better outcome was found patients with normal mental functioning (p=0.029). In our series, results for VNS are clearly inferior to resective surgery, but comparable to other treatment modalities for refractory epilepsy. With combined class I and II outcomes around 20%, and another 50% of patients having worthwhile improvement, VNS is a viable alternative when resective surgery is not feasible.

Intractable occipital lobe epilepsy: clinical characteristics and surgical treatment

Intractable occipital lobe epilepsy remains a surgical challenge. Clinical characteristics of 14 patients were analyzed. Twelve patients had surgery, seven patients had visual auras (50%) and only eight patients (57%) had posterior scalp EEG changes. Ictal single-proton emission computed tomography (SPECT) incorrectly localized in 7 of 10 patients. Six patients (50%) had Engel's class I outcome. Patients with inferior occipital seizure onset appeared to fare better (three of four class I) than patients with lateral or medial occipital seizure onset (three of eight class I). Patients who had all three occipital surfaces covered with electrodes had a better outcome (four of five class I) than patients who had limited electroencephalography (EEG) coverage (two of seven class I). Magnetic resonance imaging (MRI) lesions did not guarantee a seizure free outcome. In conclusion, visual auras, scalp EEG, and imaging findings are not reliable for correct identification of occipital onset. Occipital seizure onset can be easily missed in nonlesional epilepsy. Comprehensive intracranial EEG coverage of all three occipital surfaces leads to better outcomes.

Outcome of extratemporal epilepsy surgery experience of a single center

OBJECTIVE

Our aim was to determine the surgical outcome in adult patients with intractable extratemporal epilepsy and follow it over time.

METHODS

We retrospectively studied the operative outcome in 218 consecutive adult patients with extratemporal lesions who underwent resective surgical treatment for intractable partial epilepsy in the Bethel Epilepsy Center, Bielefeld, Germany, between 1991 and 2005. Patients were divided into three groups according to the 5-year period in which the surgical procedure took place.

RESULTS

Group I (1991-1995) consisted of 64 patients. The postoperative Engel Class I outcome was 50% at 6 months, 44.4% at 2 years, and 45.2% at 5 years. Group II (1996-2000) included 91 patients. Engel Class I outcome was 57.1% at 6 months, 53.8% at 2 years, and 53.5% at 5 years. In Group III (2001-2005), there were 63 patients. Engel Class I outcome was 65.1% at 6 months, 61.3% at 2 years, and 60.6% at 5 years. Short duration of epilepsy, surgery before 30 years of age, pathological findings of neoplasm, and well-circumscribed lesions on the preoperative magnetic resonance imaging scan were good prognostic factors. Poor prognostic factors were one or more of the following: psychic aura, generalized tonic-clonic seizure, versive seizure, history of previous surgery, and focal cortical dysplasia. On multivariate analysis, only the presence of well-circumscribed lesions on preoperative magnetic resonance imaging predicted a positive outcome (P = 0.001).

CONCLUSION

Our results indicate that extratemporal epilepsy surgery at the Bethel Epilepsy Center has become more effective in the treatment of extratemporal epilepsy patients over the years, ensuring continuous improvement in outcome. This improvement can be attributed mainly to more restrictive patient selection.

Occipital epilepsy: spatial categorization and surgical management

OBJECT

Occipital resections for epilepsy are rare. Reasons for this are the relative infrequency of occipital epilepsy, difficulty in localizing epilepsy originating in the occipital lobe, imprecisely defined seizure outcome in patients treated with focal occipital resections in the MR imaging era, and concerns about producing visual deficits. The impact of lesion location on vision and seizure biology, the management decision-making process, and the outcomes following resection need elaboration.

METHODS

The authors studied 21 consecutive patients who underwent focal occipital resections for epilepsy at Cleveland Clinic Epilepsy Center over a 13-year period during which MR imaging was used. Demographics, imaging, and data relating to the epilepsy and its surgical management were collected. The collateral sulcus, the border between the medial surface and the lateral convexity, and the inferior temporal sulcus were used to subdivide the occipital lobe into medial, lateral, and basal zones. Lesions that did not involve most or all of the occipital lobe (sublobar) were spatially categorized into these zones. Visual function, semiology, and scalp electroencephalography were evaluated in relation to these spatial categories. Preresection and postresection visual function and seizure frequency were evaluated and compared. Lastly, an exhaustive review and discussion of the published literature on occipital resections for epilepsy was carried out.

RESULTS

Five lesions were lobar and 16 were sublobar. Patients with medial or lobar lesions had a much greater likelihood of preoperative visual field defects. Those with basal or lateral lesions had a greater likelihood of having a visual aura preceding some or all of their seizures and a trend (not significant) toward having a concordant lateralized onset by scalp electroencephalography. Invasive recordings were used in 8 cases. All patients had lesions (malformations of cortical development, tumors, or gliosis) that were completely resected, as evaluated on postoperative MR imaging. At last follow-up, 17 patients (81%) were seizure free or had only occasional auras (Wieser Class 1 or 2). The remaining 4 patients (19%) had a worthwhile improvement in seizure control (Class 3 or 4). Of the patients for whom both pre- and postoperative visual testing data were available, 50% suffered no new visual deficits, and 17% each developed a new quadrantanopia or a hemianopia.

CONCLUSIONS

Lesional occipital lobe epilepsy can be successfully managed with resection to obtain excellent seizure-free rates. Individually tailored resections (in lateral occipital lesions, for example) may help preserve intact vision in a subset of cases (38% in this series). Invasive recordings may further guide surgical decision-making as delineated by an algorithm generated by the authors. The authors' results suggest that the spatial location of the lesion correlates both with the semiology of the seizure and with the presence of visual deficit.

Posterior cortex epilepsy: diagnostic considerations and surgical outcome

PURPOSE

To assess the role of various pre-surgical evaluations in posterior cortex epilepsy (PCE) and its surgical outcome.

METHODS

A retrospective analysis of clinical and laboratory data from 43 PCE patients referred for surgery was performed. The diagnosis was established by standard pre-surgical evaluation modalities including semiology, MRI, interictal and ictal scalp video-EEG as well as additional intracranial EEG monitoring in selected cases.

RESULTS

The 43 patients included 11 parietal lobe epilepsies, 13 occipital lobe epilepsies, and 19 patients with seizures originating from parieto-occipito-posterior temporal cortex. Thirty-three (76.7%) patients experienced at least one type of aura. Seventeen patients showed complex focal seizures, which were followed by secondarily generalized tonic-clonic seizures in seven of them; eighteen patients predominantly showed simple motor seizures (clonic seizures in 6, tonic seizures in 7, and versive seizures in 5). Long-term visual field deficits were observed in 8 patients. Other transient neurological deficits occurred in 7 patients. All patients received the follow-up study lasting 1-5 years, and achieved Engel's I in 26 cases, II in 5, III in 5, and IV-V in 7. Malformation of cortical development was diagnosed in 41.9% of our surgical population. No significant relationship was found between the diagnostic accuracy of any pre-surgical evaluating modality and surgical outcome in this series.

CONCLUSIONS

Surgical treatment is effective for PCE. Accurate localization of epileptogenic zone and eloquent cortex are two key factors for favorable outcome. None of the diagnostic modalities shows obvious predictive value for favorable surgical outcome.

Surgical treatment of occipital lobe epilepsy

OBJECT

Occipital lobe epilepsy (OLE) accounts for a small percentage of extratemporal epilepsies and only few and mostly small patient series have been reported. Preoperative findings, surgical strategies, histopathological bases, and postoperative outcomes for OLE remain to be elucidated.

METHODS

A group of 54 patients with occipital lobe involvement were identified from a prospective epilepsy surgery database established in 1989. Medical charts, surgical reports, MR imaging, and histopathology data were reviewed, and patients with additional temporal and/or parietal involvement were categorized separately. Seizure outcome was classified according to the Engel classification scheme (Classes I-IV). Two patients were excluded due to incomplete data sets. Fifty-two patients with intractable epilepsy involving predominantly the occipital lobe were included in the study, comprising 17.8% of 292 patients undergoing operations for extratemporal epilepsies.

RESULTS

In nearly all cases (50 [96.2%] of 52), a structural lesion was visible on preoperative MR imaging. Of these cases, 29 (55.8%) had "pure" OLE with no temporal or parietal lobe involvement. Most patients (83%) had complex partial seizures, and 60% also had generalized seizures. All patients underwent occipital lesionectomies or topectomies; 9 patients (17.3%) underwent additional multiple subpial transections. Histopathology results revealed 9 cortical dysplasias (17.3%), 9 gangliogliomas (17.3%), 6 other tumors (11.5%), 13 vascular malformations (25%), and 15 glial scars (28.8%). Visual field deficits were present in 36.4% of patients preoperatively, and 42.4% had new or aggravated visual field deficits after surgery. After a mean follow-up of 80 months, 36 patients were seizure free (69.2% Engel Class I), 4 rarely had seizures (7.7% Engel Class II), 8 improved more than 75% (15.4% Engel Class III), and 4 had no significant improvement (7.7% Engel Class IV). Multifactorial logistic regression analysis revealed that early age at epilepsy manifestation (p = 0.031) and shorter epilepsy duration (p = 0.004) were predictive of better seizure control. All other clinical and surgical factors were not significant in predicting outcome.

CONCLUSIONS

Occipital lobe epilepsy is an infrequent but significant cause of extratemporal epilepsy. Satisfactory results (Engel Class I or II) were obtained in 77% of patients in our series. Postoperative visual field deficits occurred in a significant proportion of patients. In the modern MR imaging era, lesions should be investigated in patients with OLE and lesionectomies should be performed early for a better outcome.