Bilateral mesial temporal lobe epilepsy: comparison of scalp EEG and hippocampal MRI-T2 relaxometry

Neurosurgery in feline epilepsy, including clinicopathology of feline epilepsy syndromes

Feline epilepsy is treated with antiseizure medications, which achieves fair to good seizure control. However, a small subset of feline patients with drug-resistant epilepsy requires alternative therapies. Furthermore, approximately 50 % of cats with epileptic seizures are diagnosed with structural epilepsy with or without hippocampal abnormality and may respond to surgical intervention. The presence of hippocampal pathology and intracranial tumors is a key point to consider for surgical treatment. This review describes feline epilepsy syndrome and epilepsy-related pathology, and discusses the indications for and availability of neurosurgery, including lesionectomy, temporal lobectomy with hippocampectomy, and corpus callosotomy, for cats with different epilepsy types.

Bilateral epileptogenesis in temporal lobe epilepsy due to unilateral hippocampal sclerosis: A case series

INTRODUCTION

Bitemporal epilepsy (biTLE), a potential cause of failure in TLE surgery, is rarely associated with unilateral HS and could be suggested by not lateralizing ictal scalp EEG/interictal PET-FDG findings. We evaluated the proportion of biTLE in a population of drug-resistant TLE-HS subjects who underwent intracranial investigation for lateralizing purpose.

METHODS

We retrospectively included all consecutive refractory TLE-HS patients and not lateralizing ictal scalp EEG/interictal PET-FDG findings, investigated by intracranial bilateral longitudinal hippocampal electrodes. Demographic characteristics, electroclinical findings and seizure outcome were evaluated.

RESULTS

We identified 14 subjects (7 males; mean age 39.5 years; mean age at disease onset 14.4 years), 7 of them had biTLE diagnosed after intracranial investigations. In the remaining 7 with unilateral epileptogenesis (uniTLE) anterior temporal lobectomy was performed (6/7 were in Engel class I). Preoperative neuropsychological assessment differentiated biTLE from uniTLE, as it was normal in six uniTLE patients but only in one with biTLE (p < 0.05).

CONCLUSIONS

Not lateralizing ictal scalp EEG and functional imaging findings in TLEHS should alert about the possibility of a true biTLE also in presence of unilateral findings at MRI. Intracranial investigations with bilateral longitudinal hippocampal electrodes can localize the EZ with a good risk-benefit profile. Consistently with the warning on memory functions in TLE patients explored by using longitudinal hippocampal electrodes, further studies are needed to better define the optimal investigation strategy.

Clinical significance of bilateral epileptiform discharges in temporal lobe epilepsy

OBJECTIVE

The aim of the current study was to investigate the rate and clinical significance of bitemporal interictal epileptiform discharges (IEDs) in a large cohort of patients with temporal lobe epilepsy (TLE).

METHODS

The data used in this study were collected at the Epilepsy Care Unit, Namazi Hospital, Shiraz University of Medical sciences, Shiraz, Iran, from 2008 to 2020. Inclusion criteria were a confirmed diagnosis of TLE based on the clinical grounds (history and the described seizure semiology) and a 2-hour interictal video-electroencephalography (EEG) monitoring. The EEG recording of each patient included both sleep (about 90 minutes) and wakefulness (about 30 minutes).

RESULTS

532 patients were included in this study [420 patients (79%) had unilateral IEDs, and 112 patients (21%) had bilateral IEDs]. Patients with bilateral IEDs less often had auras with their seizures and had higher frequencies of seizures (as a trend for focal to bilateral tonic-clonic seizures and significantly in focal seizures with impaired awareness) compared with those who had unilateral IEDs. Patients with bilateral epileptiform discharges showed a trend to experiencing ictal injury more frequently. Brain MRI findings were different between these two groups (p = 0.0001).

CONCLUSION

It is important to recognize that a patient with TLE has unilateral vs. bilateral IEDs. Bilateral IEDs in a patient with TLE may suggest a more severe disease (with a higher risk for ictal injuries and other significant consequences of frequent seizures). It may also suggest a somewhat different etiology.

Unusual ictal propagation patterns suggesting poor prognosis after temporal lobe epilepsy surgery: Switch of lateralization and bilateral asynchrony

OBJECTIVE

The objective of this study was to investigate unusual ictal propagation patterns in patients with drug-resistant temporal lobe epilepsy (TLE) and reveal their electrophysiological, neuroimaging, and prognostic properties after surgery.

METHODS

Among 248 patients with TLE who underwent scalp video-electroencephalographic (EEG) monitoring, 24 patients with 'switch of lateralization' or 'bilateral asynchrony' in at least one of their seizures (9.3%) were analyzed retrospectively. The postoperative outcome was determined in 16 patients who had undergone epilepsy surgery.

RESULTS

All but 5 of the included patients had hippocampal sclerosis (HS) as their magnetic resonance imaging (MRI) findings. Twelve out of 16 patients (75%) who had surgery were seizure-free for at least 1 year. Nine out of 12 patients (75%) with good outcome had unilateral interictal EEG discharges in temporal regions whereas 3 out of 4 patients with poor outcome had bilateral temporal interictal spiking (p = 0.018).

CONCLUSION

Unusual ictal propagation patterns are not always related to poor prognosis after surgery in patients with TLE. Patients with unilateral interictal spiking in the temporal region tend to have good outcome despite these unusual patterns. These patterns can also be seen in patients with TLE with other etiologies besides the well-known HS in MRI.

How Different Are the Patients With Bilateral Hippocampal Sclerosis From the Unilateral Ones Clinically?

PURPOSE

There is a lack of knowledge on consecutive patients with epilepsy associated with bilateral hippocampal sclerosis (BHS). We aimed to investigate the differentiating features of BHS in comparison with unilateral HS (UHS).

METHOD

We investigated our database for patients with epilepsy fulfilling the major magnetic resonance imaging criteria for BHS; namely, presence of bilateral atrophy and high signal changes on T2 and FLAIR series in the hippocampi. UHS patients seen in past 2 years were included as the control group. Clinical, EEG, and other laboratory findings, data on treatment response and epilepsy surgery were investigated from their files.

RESULTS

A total of 124 patients (31 with BHS and 93 with UHS; 49 right-sided and 44 left-sided) were included. We found that 16.1% of the BHS and 18.3% of the UHS groups were not drug-refractory. A binary logistic regression analysis performed with significant clinical features disclosed that history of febrile status epilepticus, mental retardation, and status epilepticus were statistically more common in BHS group. Moreover, diagnosis of psychosis established by an experienced psychiatrist and slowing of the EEG background activity were both found significantly more frequent in BHS. 66.67% of the operated BHS patients showed benefit from epilepsy surgery.

CONCLUSIONS

BHS is a heterogeneous group, showing significant differences such as increased frequencies of mental retardation, status epilepticus, febrile status epilepticus and psychosis, in comparison to UHS. In all, 16.1% of the BHS cases showed a benign course similar to the UHS group and some patients with drug-resistant epilepsy may show benefit from epilepsy surgery.

Morphological imaging of the hippocampus in epilepsy

The hippocampus is a structure frequently involved in epilepsy, especially in partial drug-resistant forms. In addition, some hippocampal pathologies are associated with specific types of epilepsy presenting specific clinical courses and requiring specific treatments. Considering these major implications for treatment, morphological investigations of the hippocampus are crucial for epileptic patients. Indeed, discovery of hippocampal sclerosis may (depending on the clinical and electrophysiological findings) lead to the diagnosis of mesial temporal lobe epilepsy (MTLE). If the diagnosis of MTLE is retained in a case of drug-resistance, surgery may be proposed without invasive phase II investigations such as stereoelectroencephalograpy. In other instances, hippocampal abnormalities may be associated with epilepsy, but without the same value for localizing the ictal onset zone. Hippocampal dysgenesis is a strong argument for non-temporo-mesial ictal onset ipsilateral to the malformation. We describe here the specific MRI modalities adapted for hippocampal investigations and the radiological signs of hippocampal pathologies associated with epilepsy (especially hippocampal sclerosis and hippocamal dysgenesis). Hippocampus morphological investigations in epilepsy require specific MRI modalities and appropriate knowledge of the specific signs of each pathology. Careful analysis is crucial since the results may have a major impact on the therapeutic management of epileptic patients.

Clinical MRI in children and adults with focal epilepsy: a critical review

Hippocampal sclerosis in adults and focal cortical dysplasia in children with epilepsy are frequent lesions, but they are overlooked on standard MRI. Errors in the interpretation of MRI in epilepsy can be attributed mainly to poor technique and perceptual misses, but incomplete knowledge and poor judgment are also possible sources. This review covers what to expect in structural MRI of an adult patient with mesial temporal lobe epilepsy (TLE) and how to find hippocampal sclerosis (HS). It also covers the clinical MRI-based detection of focal cortical dysplasia (FCD) in extratemporal lobe epilepsy, mainly in children. In a stepwise approach, first, a typical epilepsy MRI protocol at 1.5 T includes axial and coronal fluid-attenuated inversion recovery (FLAIR) imaging, T2- and T2 *-weighted images, and a T1-weighted, three-dimensional volume acquisition. Advanced MR techniques (quantitation, new contrasts like diffusion, MR spectroscopy, high-contrast high-resolution imaging on high-field MR scanners > or = 3 T) are used to increase the method's sensitivity to detect a lesion in an individual patient. Exploiting increased sensitivity, we can avoid false-positive results in the light of a clinical hypothesis, possibly isolating a localized brain area by seizure semiology and EEG prior to MR reading.

Two types of remote propagation in mesial temporal epilepsy: analysis with scalp ictal EEG

The purpose of this study was to describe the propagation pattern of ictal discharges, particularly remote patterns from a localized onset in patients with mesial temporal epilepsy, and to determine whether this provides additional information to that obtained from prolonged presurgery scalp EEG monitoring. This is a retrospective and analytical study that included a historical open cohort of 18 patients with mesial temporal epilepsy, among whom 56 regionalized-lateralized onset seizures were recorded. These seizures were analyzed as to whether remote propagation occurred and as to their temporal characteristics. Thirty-eight regionalized-lateralized onset seizures did not show remote propagation, whereas 18 did. Two types of remote propagation were identified, one early and one late, depending on whether the remote propagation occurred before or after 10 seconds had elapsed from the onset of the electroencephalographic seizure. When the seizures were compared according to the type of propagation, those with early remote propagation showed a correlation, not statistically significant, with the intractability of the epilepsy (P = 0.0754), toward independent bitemporal interictal discharges (P = 0.1667), and from the MRI perspective, to occur with temporal lesions other than pure mesial sclerosis (P = 0.6329). Early remote propagation seizures were not associated with nonlateralized onset (P = 0.2682). The only patient in our study with switch of lateralization seizures experienced early remote propagation seizures. Patients with late remote propagation seizures and those without remote propagation showed no statistically significant differences with respect to these variables. Ictal recording with scalp EEG allows for differentiating between early and late remote propagation in patients with mesial temporal epilepsy and regionalized-lateralized onset seizures. Early remote propagation probably identifies a subgroup of these patients with greater uni- or bitemporal hyperexcitability.

Contralateral 80–280Hz EEG ripples and hippocampal single unit discharge inhibition in response to acute tetanization of rat right caudate putamen in vivo

Clinically, 4-8 Hz (or 30-80 Hz) stimulation of the caudate nucleus ceases (or enhances) the neocortical and hippocampal epileptiform activities of the epilepsy patients. Possibly, electric stimulation of the caudate nucleus could produce epilepsy. In order to prove this point we delivered the acute tetanization (60 Hz, 2s, 0.4-0.6 mA) into the rat right caudate putamen nucleus (ATRC) and examined bilateral neocortical EEG and hippocampal unit discharges in vivo. The results demonstrated that: (1) 80-280 Hz EEG ripples could be evoked bilaterally, and more stronger on the contralateral side. And the maximum amplitudes of the power spectra (microV2/Hz) have higher shifting variability among multiple contralateral EEG ripples. (2) The EEG ripples were coupled contralaterally with the hippocampal neuronal firing inhibition. (3) An episode of 10-15 Hz EEG oscillations was ipsilaterally coupled with rhythmic hippocampal neuronal bursts. It suggested that the hemispheric reactions of neocortical EEG and hippocampal neuronal discharges are lateralized in response to the stimulation. It implies that the epileptic network activities were reorganized by the ATRC. Neocortical EEG ripples, called as seizure-like fast oscillations, were repetitively evoked by the ATRC.