Time from ictal subdural EEG seizure onset to clinical seizure onset: prognostic value for selecting temporal lobectomy candidates.

Long-term subdural EEG recording was performed to test the hypothesis that the duration from ictal subdural EEG seizure onset (ECOT) is prognostic for seizure-free outcome following temporal lobectomy. In 48 patients with complex partial seizures, temporal lobectomy was based on invasive localization of the ictal seizure focus. Subdural EEG data were analyzed for association with seizure-free outcome (seizure-free: yes or no) at a minimum of one year following temporal lobectomy. As the duration from ictal subdural EEG seizure onset to clinical seizure onset increased, the odds of being seizure-free postoperatively increased. The best fitting statistical model for predicting seizure-free outcome included seizure onset (unilateral vs. bilateral) and duration from ictal subdural EEG seizure onset to clinical seizure onset. While selection of temporal lobectomy candidates has increasingly emphasized noninvasive recording, some scalp-EEG monitored patients cannot be offered surgery for various reasons, one of which may include ictal EEG seizure onset following clinical seizure onset. When subdural EEG monitoring is performed for selection of temporal lobectomy candidates, analysis of the duration from subdural EEG seizure onset to clinical seizure onset should improve the prognostic value of the subdural EEG data for seizure-free outcome following temporal lobectomy.

Heart rate and heart rate variability changes in the intracarotid sodium amobarbital test.

PURPOSE: Changes in heart rate and heart rate variability have been found in prior studies performed during the intracarotid sodium amobarbital (ISA) test. However, these results are not entirely consistent with current models of differential cerebral involvement in the modulation of the heart. This study was designed to re-investigate this topic with a larger N than has heretofore been used. METHODS: The electrocardiogram was recorded during left and right ISAs in 73 subjects. Raw heart rate and heart rate variability were calculated. RESULTS: Raw heart rate increased during inactivation of either hemisphere, but more so for the right hemisphere. Heart rate variability changes consistent with decreasing parasympathetic tone also were found to occur during either ISA, but to a significant degree, only during right ISA. CONCLUSIONS: The right hemisphere appears to have a greater role in cerebral regulation of cardiac function, perhaps by virtue of the modification of parasympathetic effects.

A mathematical model of internal time processing in temporal lobe epilepsy.

Based on known relationships between epileptic and nonepileptic cortical cerebral blood flow, electrocorticographic factors and epileptogenicity, a mathematical model for internal time processing is derived. The model suggests that the human brain has mechanisms for internal processing of real, reverse and imaginary time.

Temporal lobe seizure interhemispheric propagation time depends on nonepileptic cortical cerebral blood flow.

In some patients with epilepsy, activation of eloquent cortex using various forms of environmental stimulation and mental activity may induce seizures. The increased neuronal activity resulting from cortical stimulation may be associated with increased regional cerebral blood flow. The vascular steal theory of temporal lobe epilepsy suggests that as nonepileptogenic cortical cerebral blood flow (CBFn) increases, temporal lobe epileptogenicity increases as a result, in part, of decreasing interhemispheric propagation time (IHPT). Recently, IHPT has been shown to be a quantitative electrocorticographic measure of temporal lobe epileptogenicity. In the current study, long-term combined subdural-EEG and surface cortical cerebral blood flow (CBF) monitoring was performed to test the hypothesis that IHPT depends upon CBFn. The results show that IHPT is a nonlinear (negative exponential) function of nonepileptic cortical CBF (r=0.507, df=32, t=-2.204, P<0.05). In temporal lobe epilepsy, nonepileptic cortical hypoperfusion may represent a protective mechanism for delaying interhemispheric seizure propagation. The fact that IHPT decreases exponentially with increasing CBFn suggests that small increases in CBFn should substantially decrease IHPT and increase epileptogenicity. This study confirms that inter-hemispheric propagation time depends upon perfusion of nonepileptogenic cortex.

Affective self-report during the intracarotid sodium amobarbital test: group differences.

Emotional reactions are sometimes observed during the intracarotid sodium amobarbital test. For instance, euphoric/indifference reactions can be seen during right hemisphere inactivation and catastrophic reactions may accompany left hemisphere inactivation. Less dramatic changes can also be detected in affective self-report during left and right hemisphere amobarbital tests, with more negative affect reported during left hemisphere inactivation and either neutral or mildly positive affective states reported during right hemisphere inactivation. The current study not only replicated this effect, but in addition, found significant group differences. The first group (right way) showed a pattern of affective self-report during left and right amobarbital tests entirely consistent with prior findings, while a second group (wrong way) showed results that behaved in a diametrically opposite fashion. A third group (no change) showed little, if any, difference in affective self-report during left and right amobarbital tests. The major factor distinguishing the wrong way group from the other two appeared to be an asymmetrical distribution of left and right temporal lobe lesions in the former group. In contrast, the factor differentiating the right way group from the no change group appeared to be the relative degree of left hemisphere inactivation during the left hemisphere amobarbital test. The results are discussed not only in terms of their impact on theories of cerebral lateralization for emotion, but also in terms of methodological issues in this field.

Vascular steal model of human temporal lobe epileptogenicity: the relationship between electrocorticographic interhemispheric propagation time and cerebral blood flow.

Human temporal lobe epileptogenicity (i.e. seizure frequency) depends on epileptic and non-epileptic cerebral blood flow (CBF). Increasing non-epileptic cortical CBF is associated with reduction in epileptic cortical CBF. Seizure frequency increases logarithmically with non-epileptic cortical CBF increase and epileptic cortical CBF reduction. A model of human temporal lobe epileptogenicity is derived from the mathematical equivalence to the logarithmic function of seizure frequency of (a) epileptic and non-epileptic CBF differential and (b) electrocorticographic (ECoG) interhemispheric propagation time (IHPT). The vascular steal model of human temporal lobe epileptogenicity suggests that a small CBF redistribution from non-epileptic to epileptic cortex should produce substantial reduction in temporal lobe seizure frequency in association with prolongation of IHPT. The equivalence of these CBF and ECoG parameters to the logarithmic function of seizure frequency suggests that the interhemispheric temporal lobe perfusion gradient and ECoG propagation time may be involved in the fundamental perturbation responsible for human temporal lobe epileptogenicity.

Disturbances of amino acids from temporal lobe synaptosomes in human complex partial epilepsy.

We have studied the levels of neuroactive amino acids in synaptosomes (P2 fraction) isolated from brain tissue of ten patients with medically intractable epilepsy who were undergoing temporal lobectomy. First, lateral temporal tissue (nonfocal) was removed followed by medial temporal tissue (focal). A synaptosomal fraction (P2) was immediately prepared from each tissue and analyzed for free amino acid concentrations. Statistically significant reductions were seen in glutamine and GABA concentrations in focal tissue compared to nonfocal tissue. The ratio of excitatory amino acids (aspartate and glutamate) to inhibitory amino acids (taurine and GABA) was significantly higher in focal tissue compared to nonfocal. The glutamine/glutamate ratio was significantly reduced. These data support the hypothesis that alterations in the balance between excitatory and inhibitory amino acids may be involved in the expression of epilepsy.

Quantitative analysis of hemispatial neglect in the intracarotid sodium amobarbital (ISA) test.

There are dramatic changes in the electroencephalogram of the inactivated hemisphere in the intracarotid sodium amobarbital test. One of the more profound behavioral changes during this procedure is left hemispatial neglect accompanying right hemisphere inactivation. The present study was designed to ascertain whether there was a clear relationship between the degree of hemispheric inactivation (as measured by the electroencephalogram) and the degree of left hemispatial neglect during this procedure. Sixty-nine participants undergoing right hemisphere intracarotid sodium amobarbital testing were presented with a random letter cancellation test at various points during the procedure. Neglect was quantified as significant, moderate, minimal, or none, based on how many target letters the patients missed. The simultaneous electroencephalogram from each of these testing points was spectrally analyzed and topographic maps were generated. The degree of neglect was then compared with the comparable topographic map. It was found that as the amobarbital-induced right hemispheric dysfunction regressed, the degree of neglect lessened in a systematic fashion, as did the profound electroencephalographic changes induced by the drug. Thus, there is a clear relation between the degree of hemispheric inactivation induced by the amobarbital and the degree of left hemispatial neglect. This relationship held regardless of side of hemispheric language dominance or epileptic focus. These results replicate previous findings that right hemisphere inactivation during the intracarotid sodium amobarbital test results in left hemispatial neglect. They extend these findings by clearly showing that neglect changes in a quantitative fashion (rather than being an all-or-none phenomenon) and further, show that there is a clear relationship between the severity of neglect and the degree of hemispheric dysfunction.

Cerebral blood flow and temporal lobe epileptogenicity.

Long-term surface cerebral blood flow (CBF) monitoring was performed to test the hypothesis that temporal lobe epileptogenicity is a function of epileptic cortical perfusion. Forty-three bitemporal 2-hour periictal CBF studies were performed in 13 patients. Homotopic regions of temporal cortex maintained interictal epileptic cortical hypoperfusion and nonepileptic normal cortical CBF. At 10 minutes preictus, a statistically significant, sustained increase in CBF was detected on the epileptic temporal lobe. Two minutes preictus, there was approximation of CBF in the epileptic and nonepileptic temporal lobes. Thereafter, electrocorticographic (ECoG) and clinical seizure onset occurred. The linear relationship between CBF in the two hemispheres (epileptic and nonepileptic) was the inverse of normal (y = -0.347x + 62.767, r = 0.470, df = 95, p < 0.05). The data indicated a direct linear correlation between epileptic cortical CBF and seizure interval (frequency-1), a clinical measure of epileptogenicity (r = 0.610, df = 49, p < 0.05). Epileptogenicity was also found to be a logarithmic function of the difference between nonepileptic and epileptic cortical perfusion (r = 0.564, df = 58, t = 5.20, p < 0.05). The results showed that progressive hypoperfusion of the epileptic focus correlated with a decreased seizure interval (increased epileptogenicity). Increased perfusion of the epileptic focus correlated with an increased seizure interval (decreased epileptogenicity). The fact that CBF alterations precede ECoG seizure activity suggests that vasomotor changes may produce electrical and clinical seizure onset.

Unusual early recurrence of a cerebellar pilocytic astrocytoma following complete surgical resection. Case report and review of the literature.

Pilocytic cerebellar astrocytomas are usually benign tumors with generally an excellent prognosis following complete surgical resection. The goal of surgery is total resection to minimize the risk of recurrence. In this case report, a 5-year old boy who had undergone total resection of a posterior fossa pilocytic cerebellar astrocytoma (as documented by a contrast-enhanced computed tomography (CT) scan within 24 hours following surgery), developed a massive recurrence of the tumor within four months. Both the initial histology and the sections examined after the second resection revealed features typical for a pilocytic astrocytoma with no suspicion of malignancy. This case is unusual in that it is contrary to other reports suggesting that CT-documented complete surgical resection of pilocytic astrocytomas is without recurrence, and suggests the need for vigilant radiographic and clinical follow-up of these patients even if apparent complete resection of the tumor has been achieved.

Response of human epileptic temporal lobe cortical blood flow to hyperventilation.

Bilateral long-term surface cortical cerebral blood flow (CBF) and electrocorticographic (ECoG) monitoring were performed in eight patients with complex partial seizures. In each patient, the epileptic temporal lobe was localized using ictal ECoG. Mean seizure interval (frequency-1) off anticonvulsant medication, a clinical measure of epileptogenicity, was 1.0 +/- 0.3 h (range: 0.4 to 2.5 h). During 13 interictal hyperventilation periods, 3.6 +/- 0.6 min in duration, the mean decrease in epileptic and nonepileptic temporal cortical CBF was 13.7 +/- 2.3 versus 6.4 +/- 1.9 ml/(100 g min) (t = 2.230, d.f. = 16, P < 0.05), representing 20.9% and 10.8% reduction from baseline CBF during hyperventilation, respectively. Seizure interval decreased (i.e. frequency increased) with increasing magnitude of seizure focus CBF reduction during hyperventilation. Seizure interval was significantly correlated with epileptic temporal lobe CBF decrease during hyperventilation (R = 0.763, d.f. = 5, P < 0.05). The data suggest that, compared to nonepileptic brain, epileptic temporal lobe is particularly prone to hypoperfusion during hyperventilation. Epileptogenicity is a function of this seizure focus susceptibility to ischemia. The finding of abnormal seizure focus autoregulation during hyperventilation has implication for epileptic focus localization with cerebral blood flow analysis.

Continuous regional cerebral cortical blood flow monitoring in head-injured patients.

Continuous regional cerebral cortical blood flow (rCoBF) was monitored with thermal diffusion flowmetry in 56 severely head-injured patients. Adequate, reliable data were accumulated from 37 patients (21 acute subdural hematomas, 10 cerebral contusions, 4 epidural hematomas, and 2 intracerebral hematomas). The thermal sensor was placed at the time of either craniotomy or burr hole placement. In 15 patients, monitoring was initiated within 8 hours of injury. One-third of the comatose patients monitored within 8 hours had rCoBF measurements of 18 ml per 100 g per minute or less, consistent with previous reports of significant ischemia in the early postinjury period. Initial rCoBF measurements were similar in the patients with Glasgow Coma Scale scores of 3 to 7 and in those with scores of 8 or greater. In patients with poor outcomes, rCoBF measurements did not change significantly from initial measurements; however, in those patients who had better outcomes, final rCoBF measurements were higher than initial rCoBF measurements. The patients who had better outcomes experienced normalization of rCoBF during the period of monitoring, and patients with poor outcomes had markedly reduced final rCoBF. These changes were statistically significant. When management was based strictly upon the intracranial pressure, examples of inappropriate treatment were found. For example, hyperemia and increased intracranial pressure treated with mannitol caused further rCoBF increase, and elevated intracranial pressure with low cerebral blood flow treated with hyperventilation increased the severity of ischemia. In 3 (5%) of 56 patients, wound infections developed. Continuous rCoBF monitoring in head-injured patients offers new therapeutic and prognostic insights into their management.

Quantitative analysis of the electroencephalogram in the intracarotid amobarbital procedure: II. Coherence analysis.

Thirty-seven subjects underwent bilateral internal carotid artery injections of amobarbital before surgery for intractable epilepsy. The electroencephalograms (EEG) of these patients were continuously monitored during these 74 procedures and were later subjected to quantitative analysis. Analysis of interhemispheric coherence in the delta, theta, alpha, and beta 1 bands was performed. Prominent changes occurred in interhemispheric coherence, which showed a precipitous drop in the first 2 min after amobarbital injection, followed by a gradual return to near baseline levels. These results suggest that interhemispheric relationships are significantly disrupted by intracarotid amobarbital injection.

Long-term surface cortical cerebral blood flow monitoring in temporal lobe epilepsy.

Long-term subdural surface cortical cerebral blood flow (CBF) and electrocorticographic monitoring was performed in 12 patients with complex partial seizures. A total of 40 seizures were analyzed. Baseline CBF values from nonepileptic and epileptic temporal lobe (mean +/- standard error) were 60.0 +/- 1.0 and 50.2 +/- 1.8 ml/100 g per minute, respectively (P < 0.05). In general, clinical seizure onset was preceded by a 20-minute preictal CBF increase from baseline in the epileptic temporal lobe. Peak early postictal CBF values of nonepileptic and epileptic temporal lobes were 57.7 +/- 13.3 and 89.0 +/- 21.7 ml/100 g per minute (P > 0.05) at 5.2 +/- 2.2 and 2.4 +/- 1.0 minutes (P > 0.05) after clinical seizure onset, respectively. Statistically significant differences between nonepileptic and epileptic temporal lobe CBF were detected at 50 minutes (74.0 +/- 14.2 and 37.5 +/- 9.2 ml/100 g per minute, respectively; P < 0.05) and 60 minutes (75.6 +/- 13.6 and 36.1 +/- 8.5 ml/100 g per minute, respectively; P < 0.05) postictal. The data suggest that the optimal times for CBF analysis to differentiate epileptic from nonepileptic temporal lobe are 1) during the interictal period and 2) late (50 to 60 minutes) postictal. The results of this study should improve the understanding of the dynamic cerebral perfusion patterns in the epileptic human brain.

Long-term subdural strip electrocorticographic monitoring of ictal déjà vu.

We report a series of 8 patients with ictal déjà vu. Subdural strip electrocorticographic (ECoG) monitoring localized the ictal epileptogenic focus as follows: right (n = 6) and left (n = 2) mesiotemporal lobe. In all 8 patients, the left hemisphere was dominant for language function based on intracarotid amytal testing. In 6 right-handed patients, ictal déjà vu was associated with a right temporal lobe focus. However, in the 2 left-handed patients, the ictal focus was left temporal lobe. Although ictal déjà vu localizes the epileptic focus to temporal lobe, this experimental phenomenon appears to lateralize to the hemisphere nondominant for handedness.

Quantitative analysis of the EEG in the intracarotid amobarbital procedure. I. Amplitude analysis.

Thirty-seven subjects underwent bilateral internal carotid artery injections of amobarbital prior to surgery for intractable epilepsy. The electroencephalogram (EEG) of these patients was continuously monitored during these 74 procedures and was later subjected to quantitative analysis. Topographic mapping of these data suggested that the areas of inactivation were largely restricted to the anterior 2/3 of the hemisphere injected, corresponding to the vascular distributions of the anterior and middle cerebral arteries. Graphical representation of the data demonstrated that delta and theta band activity peaked in the first 2 min post injection and decreased gradually thereafter, becoming stable at around 12 min post injection. Examination of the alpha, beta 1, and beta 2 bands suggested that activity increased and decreased more gradually than that for delta and theta, with perhaps a longer latency. Although EEG changes were most prominent in the anterior 2/3 of the inactivated hemisphere, similar (though smaller) changes were also observed in both ipsilateral and contralateral zones thought to be outside of the vascular distribution of the internal carotid artery.

Affective self-report during the intracarotid sodium amobarbital test.

Changes in internal affective state were investigated in patients undergoing the intracarotid sodium amobarbital test. It was found that when the left hemisphere was inactivated, patients rated their mood as significantly more negative than during baseline conditions. No significant change in affective state was observed during the inactivation of the right hemisphere. The findings are interpreted in terms of a differential lateralization model of emotion, in which the right hemisphere is more involved in the more powerful and salient negative affects.

Surface cortical cerebral blood flow monitoring and single photon emission computed tomography: prognostic factors for selecting temporal lobectomy candidates.

A series of 23 patients with medically intractable temporal lobe epilepsy was studied with surface cortical cerebral blood flow monitoring, single photon emission computed tomography (SPECT) and subdural strip electrocorticographic (ECoG) monitoring for localization of the seizure focus. All patients underwent anterior temporal lobectomy and seizure outcome was determined after a mean of 9 months (range: 3-17 months). Invasive and non-invasive cerebral blood flow (CBF) parameters with prognostic value for seizure-free outcome were: (a) inter-ictal seizure focus with CBF < 65 ml/100 gm-min; (b) inter-ictal seizure focus CBF < or = normal temporal lobe CBF; and (c) concordance of inter-ictal and/or early post-ictal SPECT and ictal ECoG for seizure focus localization. These results should improve prognostic value of invasive and non-invasive cerebral blood flow data for selection of temporal lobectomy candidates.

The association of multiple personality and temporolimbic epilepsy. Intracarotid amobarbital test observations.

OBJECTIVE: What is the relationship of "multiple personality disorder" in patients with temporolimbic epilepsy to certain types of hemispheric interaction? DESIGN: Case series. SETTING: Tertiary care referral center. PATIENTS: Two patients with temporolimbic epilepsy considered to be surgical candidates referred for the intracarotid amobarbital sodium procedure (IAP). Each individual had presented with different "personalities" in a characteristic temporal relationship to their seizures. INTERVENTIONS: Intracarotid amobarbital sodium procedure, Wada test, and electroencephalogram. MAIN OUTCOME MEASURES: Behavioral observations made during the performance of the IAP. RESULTS: During the IAP, each patient's peri-ictal "personality" changes were precisely replicated. No seizure activity was noted during the IAPs. CONCLUSIONS: These observations suggest that the association of multiple personality and temporolimbic epilepsy is not dependent on seizure discharges per se, but rather may be related to certain types of hemispheric interaction.

Lumbar cerebral spinal fluid drainage during long-term electrocorticographic monitoring with subdural strip electrodes: elimination of cerebral spinal fluid leak.

We performed this study to determine the efficacy of continuous lumbar cerebral spinal fluid (CSF) drainage in controlling CSF leak during subdural strip electrode monitoring of epilepsy patients. Subdural strip electrodes were placed in 14 patients. In seven patients, a lumbar sub-arachnoid catheter was placed for continuous CSF drainage. In seven patients, no lumbar drain was placed. The duration of scalp CSF leak during strip electrode monitoring was significantly reduced in patients undergoing lumbar CSF drainage compared to those without lumbar drains (chi 2 = 40.9, P < 0.05). In one patient spinal headache developed which resolved with lumbar drain removal. Lumbar drainage eliminates scalp CSF leakage and can improve patient comfort. This technique should be further studied to determine if it reduces infection risk during long-term invasive monitoring.