Effects of Anterior Temporal Lobectomy Apart from the Relief of Seizures: A Study of 40 Patients

The effect of temporal lobectomy, apart from the relief of seizures, is described in 40 patients undergoing the operation and followed up for between 2 and 6 years. Changes in their intellectual performance and mental state are described, and the possible mechanisms of these changes are discussed.

The evolution of epilepsy surgery

This review traces the evolution of epilepsy surgery from its early beginnings in the 20th century with the development of neurophysiology, and later the identification of pathology in surgical specimens, to the tremendous boost given by direct brain imaging in the late 20th century. This resulted in the sophisticated methods of presurgical investigation, surgical techniques, and postsurgery care available from the millennium. In parallel, functional surgery, which modifies the nervous system's behaviour, available throughout, has attained a greater place by the use of stimulation.

Long-term clinical and positron emission tomography outcome of fetal striatal transplantation in Huntington's disease

Two patients with moderate Huntington's disease (HD) received bilateral fetal striatal allografts. One patient demonstrated, for the first time, increased striatal D2 receptor binding, evident with 11C-raclopride positron emission tomography, and prolonged clinical improvement over 5 years, suggesting long term survival and efficacy of the graft. The other patient did not improve clinically or radiologically. Our results indicate that striatal transplantation in HD may be beneficial but further studies are needed to confirm this.

Ipsilesional and contralesional sensorimotor function after hemispherectomy: differences between distal and proximal function

Previous studies have reported mainly on contralesional somatosensory and motor function after hemispherectomy. So far, ipsilesional impairments have received little attention even though these have been reported in patients with less extensive lesions. In the current study we assessed ipsilesional and contralesional sensorimotor function in a group of 12 patients with hemispherectomy. In addition, we focused on differences between distal and proximal function and investigated several factors that may have contributed to individual differences between patients. The tests included tapping, force production, tactile double simultaneous stimulation, pressure sensitivity, passive joint movement sense and sensitivity to hot and cold. Ipsilesional impairments were found on all tests, except passive joint movement sense. Unexpectedly, no significant ipsilateral distal-proximal gradient was found for any of the measures. Both the removal of the diseased cerebral hemisphere and possible changes to the remaining brain structures may have affected ipsilesional sensorimotor function. Contralesional performance was impaired on all tests except for passive joint movement in the shoulder. The contralesional impairments were characterized by a distal-proximal gradient measured on all tests, except that of sensitivity to hot and cold. Distal function was always most impaired. The difference between distal and proximal motor function is in agreement with the established concepts of the motor pathways, with the motoneurons innervating proximal muscles receiving bilateral cortical and subcortical input. Age at onset of original brain damage correlated significantly with passive joint movement sense. Patients with known abnormalities to the remaining brain structures performed inferior on the tapping test only. No effect was found of the hemispheric side of removal.

Is it worth pursuing surgery for epilepsy in patients with normal neuroimaging?

OBJECTIVE

To determine whether it is worth pursuing surgery for the treatment of epilepsy in patients with normal neuroimaging.

METHODS

Two patient populations were studied: (1) 136 consecutive patients who were surgically treated; (2) 105 consecutive patients assessed with chronically implanted intracranial electrodes within the same period. Sixty patients belonged to both groups, and included all 21 patients who had normal neuroimaging.

RESULTS

There were no differences in the proportion of patients with favourable outcome between those with normal and those with abnormal neuroimaging, irrespective of whether intracranial recordings were required. Among the 19 operated patients with normal neuroimaging, 74% had a favourable outcome (Engel's seizure outcome grades I and II), and among the 93 patients with abnormal neuroimaging, 73% had favourable outcome (p = 0.96). In patients with temporal resections, 92% of the 13 patients with normal neuroimaging had a favourable outcome, whereas among the 70 patients with abnormal neuroimaging, 80% had a favourable outcome (p = 0.44). In patients with extratemporal resections, two of the six patients with normal neuroimaging had a favourable outcome, while 12 of the 23 patients with abnormal neuroimaging had a favourable outcome (p = 0.65). Among the 105 patients studied with intracranial electrodes, five suffered transitory deficits as a result of implantation, and two suffered permanent deficits (one hemiplegia caused by haematoma and one mild dysphasia resulting from haemorrhage).

CONCLUSIONS

It is worth pursuing surgery in patients with normal neuroimaging because it results in good seizure control and the incidence of permanent deficits associated with intracranial studies is low.

Impaired dimensional selection but intact use of reward feedback during visual discrimination learning in Parkinson's disease

It has been suggested that Parkinson's disease (PD) impairs the ability to learn on the basis of reward or reinforcing feedback i.e., by trial-and-error. In many learning tasks, particular 'dimensions' of stimulus information are relevant whilst others are irrelevant; therefore, efficient performance depends on identifying the dimensions of these 'compound' stimuli and selecting the relevant dimension for further processing. We investigated the ability of patients with PD, as well as patients with Huntington's disease and patients with frontal or temporal lobe lesions, to learn visual discriminations which required either a number of associations to be learned concurrently (the 'eight-pair' task) or the selection of information from compound stimuli (the 'five-dimension' task), both tasks being learned by trial-and-error. None of the basal ganglia disorder patient groups was impaired on the eight-pair task, militating against a crucial role for these brain structures in trial-and-error learning per se. Patients with mild, medicated PD, but not unmedicated PD patients, were impaired at identifying all five feature dimensions in the five-dimension task, implying dopaminergic 'overdosing' of the ability to analyse compound stimuli in terms of their component dimensions. Temporal lobe lesion patients performed similarly, suggesting that the temporal lobe may be the site of the medication overdose effect. Patients with severe, medicated PD were impaired at compound discrimination learning on the five-dimension task in the absence of an underlying impairment in identifying component stimulus dimensions; this pattern resembled that seen in Huntington's disease and frontal lobe lesion patients, implying that fronto-striatal circuitry is involved in the formation of rules based upon selected stimulus dimensions.

Single-pulse electrical stimulation identifies epileptogenic frontal cortex in the human brain

OBJECTIVE

To assess the value of single-pulse electrical stimulation (SPES) to identify frontal epileptogenic cortex during presurgical assessment.

METHODS

SPES (1-millisecond pulses, 4 to 8 mA, 0.1 Hz) has been used during chronic recordings in 30 patients with intracranial electrodes in the frontal lobes. As a result of presurgical assessment, 17 patients were considered to have frontal epilepsy and 13 extrafrontal epilepsy.

RESULTS

Two types of responses to SPES were seen: 1) early responses: starting immediately after the stimulus and considered as normal responses; 2) late responses: two types of responses seen in some areas after the initial early response: a) delayed responses: spikes or sharp waves occurring between 100 milliseconds and 1 second after stimulation. Frontal delayed responses were seen in 11 frontal patients and 1 extrafrontal patient, whereas extrafrontal delayed responses were seen in 1 frontal and 10 extrafrontal patients. b) Repetitive responses: two or more consecutive sharp-and-slow-wave complexes, each resembling the initial early response. Repetitive responses were seen only when stimulating the frontal lobes of 10 frontal patients. Among the 17 frontal patients, 13 had late responses exclusively in the epileptogenic frontal lobe, whereas only 3 showed them in both frontal lobes. Frontal late responses were associated with neuropathologic abnormalities, and complete resection of abnormal SPES areas was associated with good postsurgical seizure outcome.

CONCLUSIONS

Single-pulse electrical stimulation (SPES) could be an important additional investigation during presurgical assessment to identify frontal epileptogenicity. SPES can be useful in patients who have widespread or multiple epileptogenic areas, normal neuroimaging, or few seizures during telemetry.

The impact of early and late damage to the human amygdala on ‘theory of mind’ reasoning

There is a burgeoning interest in the neural basis of the ability to attribute mental states to others; a capacity referred to as 'theory of mind' (ToM). We examined the effects of lesions of the amygdala which arise at different stages of development on this key aspect of social cognition. Tests of ToM, executive and general neuropsychological function were given to subjects with lesions of the amygdala arising congenitally or in early childhood ('early damage', n = 15), subjects who acquired damage to the amygdala in adulthood ('late damage' n = 11) and matched clinical (n = 14) and healthy comparison groups (n = 38). Subjects with early damage to the amygdala, particularly if the lesion was associated with childhood onset of seizures, were impaired relative to all other groups on more advanced tests of ToM reasoning, such as detecting tactless or ironic comments or interpreting non-literal utterances. These deficits held for subjects with either left or right early amygdala damage and encompassed the understanding of both the beliefs and emotional states of others. In contrast, subjects who acquired damage to the amygdala in adulthood (usually as part of an anterior temporal lobectomy) were not impaired in ToM reasoning relative to both clinical and healthy controls, supporting the position that the amygdala is not part of the neural circuitry mediating the 'on-line' performance of ToM reasoning. In line with theories which claim that ToM is an independent faculty of cognition, we found that the pattern of results held after co-varying for measures of executive function, memory and general intellectual functioning. We discuss the results in the light of recent theories which link early developmental insults to the amygdala with the ToM impairments which are thought to be a core neurocognitive deficit found in disorders such as autism. We conclude that the amygdala may play an important role in the neural systems supporting the normal development of ToM reasoning.

Reward-related Reversal Learning after Surgical Excisions in Orbito-frontal or Dorsolateral Prefrontal Cortex in Humans

Neurophysiological studies in primates and neuroimaging studies in humans suggest that the orbito-frontal cortex is involved in representing the reward value of stimuli and in the rapid learning and relearning of associations between visual stimuli and rewarding or punishing outcomes. In the present study, we tested patients with circumscribed surgical lesions in different regions of the frontal lobe on a new visual discrimination reversal test, which, in an fMRI study (O'Doherty, Kringelbach, Rolls, Hornak, & Andrews, 2001), produced bilateral orbito-frontal cortex activation in normal subjects. In this task, touching one of two simultaneously presented patterns produced reward or loss of imaginary money delivered on a probabilistic basis to minimize the usefulness of verbal strategies. A number of types of feedback were present on the screen. The main result was that the group of patients with bilateral orbito-frontal cortex lesions were severely impaired at the reversal task, in that they accumulated less money. These patients often failed to switch their choice of stimulus after a large loss and often did switch their choice although they had just received a reward. The investigation showed that bilateral lesions were required for this deficit, since patients with unilateral orbito-frontal cortex (or medial prefrontal cortex) lesions were not impaired in the probabilistic reversal task. The task ruled out a simple motor disinhibition as an explanation of the deficit in the bilateral orbito-frontal cortex patients, in that the patients were required to choose one of two stimuli on each trial. A comparison group of patients with dorsolateral prefrontal cortex lesions was in some cases able to do the task, and in other cases, was impaired. Posttest debriefing showed that all the dorsolateral prefrontal patients who were impaired at the task had failed to pay attention to the crucial feedback provided on the screen after each trial about the amount won or lost on each trial. In contrast, all dorsolateral patients who paid attention to this crucial feedback performed normally on the reversal task. Further, it was confirmed that the bilateral orbito-frontal cortex patients had also paid attention to this crucial feedback, but in contrast had still performed poorly at the task. The results thus show that the orbital prefrontal cortex is required bilaterally for monitoring changes in the reward value of stimuli and using this to guide behavior in the task; whereas the dorsolateral prefrontal cortex, if it produces deficits in the task, does so for reasons related to executive functions, such as the control of attention. Thus, the ability to determine which information is relevant when making a choice of pattern can be disrupted by a dorsolateral lesion on either side, whereas the ability to use this information to guide behavior is not disrupted by a unilateral lesion in either the left or the right orbito-frontal cortex, but is severely impaired by a bilateral lesion in this region. Because both abilities are important in many of the tasks and decisions that arise in the course of daily life, the present results are relevant to understanding the difficulties faced by patients after surgical excisions in different frontal brain regions.

Neuropsychological effects associated with temporal lobectomy and amygdalohippocampectomy depending on Wada test failure

OBJECTIVE

To compare the neuropsychological effects of temporal lobectomy (TL) and amygdalohippocampectomy (AH), depending on whether the patients had passed or failed the Wada test.

METHODS

We compared changes in neuropsychological scores in patients who underwent TL (n = 91) or AH (n = 15), and had passed or failed the Wada test. Comparisons were carried out in all 106 patients and among the 20 patients who failed the Wada test (12 who had TL and 8 who had AH).

RESULTS

No patient became globally amnesic after surgery. Among all patients, no differences were found in pre-surgical or change scores (percentage of change after surgery compared with preoperative values) of neuropsychological tests between patients who underwent TL or AH. Among patients who failed the Wada test, those in the TL group showed higher visual memory impairment (p<0.05). There was a strong trend suggesting that TL is associated with higher verbal memory deficits than AH (p = 0.07). Of those TL patients who failed the Wada test, the contralateral Wada score correlated with change scores in verbal intelligence quotient (p<0.01), and there was a strong trend towards a correlation with the logical memory immediate recall version subtest of the Wechsler Memory Scale (p = 0.06).

CONCLUSIONS

No profound changes in intelligence quotient or memory scores were found after TL or AH. Nevertheless, patients who underwent TL and failed the Wada test showed more deficits than those who passed the test or those who had AH. The presence of a correlation between contralateral Wada scores and verbal deficits in TL patients who failed the Wada test but not among AH patients suggests that, if temporal surgery is required, AH might be preferred to TL in patients who fail the Wada test.

Changes in emotion after circumscribed surgical lesions of the orbitofrontal and cingulate cortices

To analyse the functions of different parts of the prefrontal cortex in emotion, patients with different prefrontal surgical excisions were compared on four measures of emotion: voice and face emotional expression identification, social behaviour, and the subjective experience of emotion. Some patients with bilateral lesions of the orbitofrontal cortex (OFC) had deficits in voice and face expression identification, and the group had impairments in social behaviour and significant changes in their subjective emotional state. Some patients with unilateral damage restricted to the OFC also had deficits in voice expression identification, and the group did not have significant changes in social behaviour or in their subjective emotional state. Patients with unilateral lesions of the antero-ventral part of the anterior cingulate cortex (ACC) and/or medial Brodmann area (BA) 9 were, in some cases, impaired on voice and face expression identification, had some change in social behaviour, and had significant changes in their subjective emotional state. Patients with unilateral lesions of the OFC and of the ACC and/or medial BA 9 were, in some cases, impaired on voice and face expression identification, had some changes in social behaviour, and had significant changes in their subjective emotional state. Patients with dorsolateral prefrontal cortex lesions or with medial lesions outside ACC and medial BA 9 areas (dorsolateral/other medial group) were unimpaired on any of these measures of emotion. In all cases in which voice expression identification was impaired, there were no deficits in control tests of the discrimination of unfamiliar voices and the recognition of environmental sounds. Thus bilateral or unilateral lesions circumscribed surgically within the OFC can impair emotional voice and/or face expression identification, but significant changes in social behaviour and in subjective emotional state are related to bilateral lesions. Importantly, unilateral lesions of the ACC (including some of medial BA 9) can produce voice and/or face expression identification deficits, and marked changes in subjective emotional state. These findings with surgically circumscribed lesions show that within the prefrontal cortex, both the OFC and the ACC/medial BA 9 region are involved in a number of aspects of emotion in humans including emotion identification, social behaviour and subjective emotional state, and that the dorsolateral prefrontal areas are not involved in emotion in these ways.

VNS in patients with previous unsuccessful resective epilepsy surgery: antiepileptic and psychotropic effects

OBJECTIVES

To assess the efficacy of vagus nerve stimulation (VNS) in patients with medically and surgically intractable complex partial seizures (CPS).

PATIENTS AND METHODS

Sixteen patients with previous temporal [15] and frontal [one] resections were treated with VNS between 1994 and 1999 at King's College Hospital, London, UK. Post-operative video-electroencephalogram telemetry had shown that CPS started from the operated side in 12 patients, contralaterally in three and bilaterally independently in one.

RESULTS

Three patients (18.75%) had 50% or more reduction in seizure frequency, but one showed severe worsening of epilepsy, which remitted upon VNS discontinuation. The antiepileptic effect of VNS was not different with respect to the type of operation (anterior temporal lobectomy vs amygdalohippocampectomy), the side of operation, or the side of seizure onset. We observed psychotropic effects in two patients with post-ictal psychosis, in two others with depression, and in a child with severe behavioral disorder.

CONCLUSIONS

VNS may have a rather limited antiepileptic role to play in patients with persistent seizures following epilepsy surgery, but may independently possess useful antipsychotic and mood-stabilizing properties.

Postictal psychosis after temporal lobectomy

Three of 282 consecutive patients who had temporal resections for intractable epilepsy developed postoperative postictal psychosis. These three patients had seizure recurrence contralateral to the resection, whereas none of the patients with ipsilateral seizure recurrence developed any psychiatric symptoms after surgery. Two had left amygdalo-hippocampectomy and one right temporal lobectomy. The de novo occurrence of postoperative postictal psychosis is a well-defined complication of surgery for temporal lobe epilepsy, and may relate to contralateral epileptogenesis.

Responses to single pulse electrical stimulation identify epileptogenesis in the human brain in vivo

The aim of the present study was to investigate in vivo cortical excitability in the human brain. We studied 45 consecutive patients with refractory epilepsy in whom subdural or intracerebral electrodes were implanted for assessment prior to epilepsy surgery. We compared cortical responses to single pulse stimulation (up to 8 mA, 1 ms duration) in areas where seizure onset occurred, with responses recorded elsewhere. Two main types of responses were seen: (i) 'early responses', spikes and/or slow waves starting within 100 ms after the stimulus which were observed in most regions in all patients; and (ii) 'delayed responses', spikes or sharp waves occurring between 100 ms and 1 s after stimulation which were seen in some regions in 27 patients. The distributions of early and delayed responses were compared with the topography of seizure onset. Whereas early responses were seen in most regions and seem to be a normal response of the cortex to single pulse stimulation, the distributions of delayed responses were significantly associated with the regions where seizure onset occurred. We conclude that the presence of delayed responses can identify regions of hyperexcitable cortex in the human brain. The study of delayed responses may improve our understanding of the physiology and dynamics of neuronal circuits in epileptic tissue and may have an immediate clinical application in assessment of candidates for surgical treatment of epilepsy.

Lateralizing and localizing values of ictal onset recorded on the scalp: evidence from simultaneous recordings with intracranial foramen ovale electrodes

PURPOSE

The value of scalp recordings to localize and lateralize seizure onset in temporal lobe epilepsy has been assessed by comparing simultaneous scalp and intracranial foramen ovale (FO) recordings during presurgical assessment. The sensitivity of scalp recordings for detecting mesial temporal ictal onset has been compared with a "gold standard" provided by simultaneous deep intracranial FO recordings from the mesial aspect of the temporal lobe. As FO electrodes are introduced via anatomic holes, they provide a unique opportunity to record simultaneously from scalp and mesial temporal structures without disrupting the conducting properties of the brain coverings by burr holes and wounds, which can otherwise make simultaneous scalp and intracranial recordings unrepresentative of the habitual EEG.

METHODS

Simultaneous FO and scalp recordings from 314 seizures have been studied in 110 patients under telemetric presurgical assessment for temporal lobe epilepsy. Seizure onset was identified on scalp records while blind to recordings from FO electrodes and vice versa.

RESULTS

Bilateral onset (symmetric or asymmetric) was more commonly found in scalp than in FO recordings. The contrary was true for unilateral seizure onset. In seizures with bilateral asymmetric onset on the scalp, the topography of largest-amplitude scalp changes at onset does not have localizing or lateralizing value. However, 75-76% of seizures showing unilateral scalp onset with largest amplitude at T1/T2 or T3/T4 had mesial temporal onset. This proportion dropped to 42% among all seizures with a unilateral scalp onset at other locations. Of those seizures with unilateral onset on the scalp at T1/T2, 65.2% showed an ipsilateral mesial temporal onset, and 10.9% had scalp onset incorrectly lateralized with respect to the mesial temporal onset seen on FO recordings. In seizures with a unilateral onset on the scalp at electrodes other than T1/T2, the proportions of seizures with correctly and incorrectly lateralized mesial temporal onset were 37.5 and 4.2%, respectively. Thus the ratio between incorrectly and correctly lateralized mesial temporal onsets is largely similar for seizures with unilateral scalp onset at T1/T2 (16.7%) and for seizures with unilateral scalp onset at electrodes other than T1/T2 (11.2%). The onset of scalp changes before the onset of clinical manifestations is not associated with a lower proportion of seizures with bilateral onset on the scalp, or with a higher percentage of mesial temporal seizures or of mesial temporal seizures starting ipsilateral to the side of scalp onset. In contrast, the majority (78.4%) of mesial temporal seizures showed clinical manifestations starting after ictal onset on FO recordings.

CONCLUSIONS

A bilateral scalp onset (symmetric or asymmetric) is compatible with a mesial temporal onset, and should not deter further surgical assessment. Although a unilateral scalp onset at T1/T2 or T3/T4 is associated with a higher probability of mesial temporal onset, a unilateral onset at other scalp electrodes does not exclude mesial temporal onset. A unilateral scalp onset at electrodes other than T1/T2 is less likely to be associated with mesial temporal onset, but its lateralizing value is similar to that of unilateral scalp onset at T1/T2. The presence of clinical manifestations preceding scalp onset does not reduce the localizing or lateralizing values of scalp recordings.

Unilateral fixed dilation of the pupil as a false-localizing sign with intracranial hemorrhage: case report and literature review

OBJECTIVE AND IMPORTANCE

Although other focal signs may prove "false localizing," it is a neurosurgical axiom that unilateral fixed dilation of the pupil occurs ipsilateral to a supratentorial mass.

CLINICAL PRESENTATION

A 25-year-old man collapsed with a dense right hemiplegia and a Glasgow Coma Scale score of 6 (eye opening, 1; motor, 4; verbal, 1) after rupture of a left middle cerebral artery aneurysm associated with an intrasylvian hematoma. Initially, both pupils had remained equal-sized and reactive: however, within hours, the right (contralateral) pupil became fixed and dilated (i.e., false localizing). For some time, the left (ipsilateral) pupil remained small and reactive; at emergency craniotomy, this also became fixed and equally dilated.

INTERVENTION

After evacuation of the clot and wrapping of the aneurysm, both pupils rapidly became equal-sized and reactive. Twenty-four hours later, concurrent with massive left hemispheric swelling and a midline shift, the left (ipsilateral) pupil became unilaterally fixed and dilated (i.e., false localizing). Eventually, the right (contralateral) pupil also became fixed and dilated, concurrent with cardiovascular collapse. Death occurred within 10 hours.

CONCLUSION

Unilateral fixed dilation of the pupil in patients with hemispheric mass lesions may be false localizing. Furthermore, disparate "herniating mechanisms" can arise despite mass effect emanating from the same side. Because such mechanisms cannot be witnessed, their nature remains speculative. An extensive review is contained in this article.

Prognostic factors in the surgical treatment of medically intractable epilepsy associated with mesial temporal sclerosis

OBJECTIVES

To assess the prognostic factors determining seizure remission after temporal lobectomy for intractable epilepsy associated with mesial temporal sclerosis (MTS) at pathology.

METHODS

The clinical and investigative features of 116 consecutive patients who had temporal lobe surgery for drug-resistant epilepsy and MTS at pathology were assessed using actuarial statistics and logistic regression analysis.

RESULTS

At a median follow-up of 63 months the probability of achieving at least a 1-year period of continuous seizure freedom was 67%. Factors contributing to a favourable outcome were interictal EEG localization to the operated lobe and the absence of secondarily generalized seizures. These were also selected in the multivariate analysis, although at lower statistical significance (P=0.08 and 0.09, respectively). Perinatal complications were associated with a significantly worse outcome but overall, complicated febrile convulsions and congruent neuropsychological deficits were not significantly predictive variables.

CONCLUSIONS

The present findings may aid in the non-invasive presurgical assessment of patients with intractable TLE and clinical and neuroimaging evidence of MTS.

The urgent postoperative CT scan: a critical appraisal of its impact

Urgent CT scanning of critically ill neurosurgical patients is costly, labour intensive and associated with some risk. A study of urgent postoperative CT scans was carried out to assess the proportion that changed patient management. A further study evaluated the accuracy of predicting a haematoma. A retrospective analysis was carried out over a 6-month period of all scans performed within 48 h of craniotomy. This was followed by a prospective comparison between the surgeon's estimate of the chance of a haematoma on the scan and the scan result. Of 184 patient undergoing craniotomy, 40 patients (22%) were scanned within 48 h. Five patients were re-operated for haematoma formation. Prospective assessment showed that surgeons consistently over-estimated the risk at haematoma (mean prescan estimate 63%, actual risk 8%, p = 2.5 x 10(-12)). Less than 1 in 10 postoperative scans show a neurosurgical target. Other changes in management following scanning were slight.

Path integration following temporal lobectomy in humans

Path integration, a component of spatial navigation, is the process used to determine position information on the basis of information about distance and direction travelled derived from self-motion cues. Following on from studies in the animal literature that seem to support the role of the hippocampal formation in path integration, this facility was investigated in humans with focal brain lesions. Thirty-three neurosurgical patients (17 left temporal lobectomy, LTL; 16 right temporal lobectomy, RTL) and 16 controls were tested on a number of blindfolded tasks designed to investigate path integration and on a number of additional control tasks (assessing mental rotation and left-right orientation). In a test of the ability to compute a homing vector, the subjects had to return to the start after being led along a route consisting of two distances and one turn. Patients with RTL only were impaired at estimating the turn required to return to the start. On a second task, route reproduction was tested by requiring the subjects to reproduce a route consisting of two distances and one turn; the RTL group only were also impaired at reproducing the turn, but this impairment did not correlate with the homing vector deficit. There were no group differences on tasks where subjects were required to reproduce a single distance or a single turn. The results indicate that path integration is impaired in RTL patients only and suggest that the right temporal lobe plays a role in idiothetic spatial memory.

Predictors of outcome and pathological considerations in the surgical treatment of intractable epilepsy associated with temporal lobe lesions

OBJECTIVES

To evaluate the influence of clinical, investigative, and pathological factors on seizure remission after temporal lobectomy for medically intractable epilepsy associated with focal lesions other than hippocampal sclerosis.

METHODS

From a series of 234 consecutive "en bloc" temporal resections for medically intractable epilepsy performed between 1976 and 1995, neuropathological examination disclosed a focal lesion in 80. The preoperative clinical, neuropsychological, interictal EEG, and neuroimaging characteristics of these patients were assembled in a computerised database. The original neuropathological material was re-examined for lesion classification and completeness of removal. The presence of additional cortical dysplasia and mesial temporal sclerosis was also noted. Survival analysis was performed using Kaplan-Meier curves and actuarial statistics. Logistic regression analysis was used to establish the independent significance of the clinical variables.

RESULTS

The probability of achieving a 1 year seizure remission was 71% by 5 years of follow up. Factors predicting a poor outcome on multivariate analysis included the need for special schooling and a long duration of epilepsy. Generalised tonic-clonic seizures, interictal EEG discharges confined to the resected lobe, demonstration of the lesion preoperatively on CT, and complete histological resection of the lesion were not predictive of outcome. Neuropsychological tests correctly predicted outcome in left sided cases but apparently congruent findings in right sided resections were associated with a poor outcome. Pathological reclassification established the dysembryoplastic neuroepithelial tumour as the commonest neoplasm (87%) in this series, with a significantly better seizure outcome than for developmental lesions, such as focal cortical dysplasia.

CONCLUSIONS

The findings highlight the importance of dysembryoplastic neuroepithelial tumour in the pathogenesis of medically refractory lesional temporal lobe epilepsy and the prognostic significance of preoperative duration of epilepsy emphasises the need for early recognition and surgical treatment. Cognitive and behavioural dysfunction, however, is associated with a lower seizure remission rate, independent of duration of epilepsy.

Chronic encephalitis and temporal lobe epilepsy: a variant of Rasmussen's syndrome?

The authors report two adult patients with chronic temporal lobe epilepsy and pathologic features consistent with Rasmussen's encephalitis. Although seizures persisted after temporal lobe surgery no progressive cognitive or neurologic deficit has emerged. Prominent auditory auras in each suggested a persisting epileptogenic focus in the superior temporal gyrus. The current findings expand the clinical spectrum of Rasmussen's encephalitis and suggest that chronic nonprogressive encephalitis may serve as the pathologic substrate of medically intractable temporal lobe epilepsy.

Relevance of residual histologic and electrocorticographic abnormalities for surgical outcome in frontal lobe epilepsy

PURPOSE

To estimate the significance of residual electrocorticographic and neuropathologic abnormalities on seizure control after surgery for frontal lobe epilepsy with the purpose of determining their relevance in deciding the extent of the surgical procedure.

METHODS

The presence of epileptiform discharges in intraoperative electrocorticograms (ECoGs) and the nature and extent of neuropathologic abnormalities were reviewed for 35 patients who underwent frontal lobe resections for the treatment of epilepsy at our institution. The relations between surgical outcome and presence of the following features were studied: (a) presence of abnormal tissue at the limits of the resection; (b) presence of sporadic spikes and seizure patterns in the preresection ECoG; (c) their abolition in the postresection ECoG; and (d) the topography of residual discharges with respect to the margins of the resection.

RESULTS

On neuropathologic examination, 18 patients showed focal cortical dysplasia (CD), and 17 showed other abnormalities (non-CD). Ten CD patients and 11 non-CD patients experienced a favourable outcome. Seizure patterns were significantly more common in patients with focal cortical dysplasia than in those without, with a sensitivity of 94% and a specificity of 75%. Abolition of seizure patterns was associated with a favourable surgical outcome (p = 0.031). Abolition of sporadic spikes or their presence in the postresection ECoG did not influence outcome. There was no clear relation between outcome and location of residual sporadic discharges. Seizure patterns persisted in the postresection ECoG in three CD patients, were located at the margins of the resection in all three, and these patients had a poor outcome. Incomplete removal of abnormal tissue was not associated with a poorer outcome in either patient group or in the complete sample.

CONCLUSIONS

Seizure patterns were significantly more common in patients with cortical dysplasia, and their abolition on postresection ECoG recordings was associated with a favourable surgical outcome. Persistence of sporadic ECoG spikes and incomplete removal of histologic abnormalities did not affect outcome significantly.

"Theory of mind" impairments and their relationship to executive functioning following frontal lobe excisions

It has been suggested that mental states play an important role in determining behaviour and that mental state attributions ("theory of mind") underlie the ability to understand and predict other peoples' behaviour. Theory of mind was investigated in 31 patients with unilateral frontal lobe lesions (15 right-sided and 16 left-sided) by comparing their performance with that of 31 matched control subjects. The ability to infer first- and second-order beliefs was tested by requiring subjects to listen to stories in which a protagonist acted upon a false belief. Both patient groups exhibited significantly impaired performance on the two theory of mind measures. Both frontal lobe groups also exhibited a range of deficits in tests of executive functions, but analyses revealed that these seemed to be independent of theory of mind impairments. These findings are discussed in terms of the hypothesis of a specialized, adaptive brain system underlying theory of mind reasoning ability, and are related to observed difficulties in social functioning among patients with frontal lobe damage.

Sensitivity of recordings at sphenoidal electrode site for detecting seizure onset: evidence from scalp, superficial and deep foramen ovale recordings

OBJECTIVES

Some authors have recently stressed that the position of the tip of sphenoidal electrodes plays a crucial role in their efficacy in detecting ictal onset. An opportunity to test this hypothesis is provided by recordings from the most superficial contacts of foramen ovale (FO) electrode bundles because these contacts are located at the FO, in a position equivalent to that of optimally located sphenoidal electrodes. To simplify wording, recordings obtained by superficial FO electrodes will hereafter be called sphenoidal recordings, although they have not been obtained with standard sphenoidal electrodes. The sensitivities of simultaneous scalp and sphenoidal recordings for detecting ictal onset have been compared with each other, and with a 'gold standard' provided by simultaneous deep intracranial FO recordings from the mesial aspect of the temporal lobe.

METHODS

Three hundred and fourteen seizures obtained from 110 patients under telemetric presurgical assessment for temporal lobe epilepsy have been studied. Scalp electrodes included anterior temporal placements. All scalp electrodes were considered when identifying seizure onset but the anterior temporal electrodes were most frequently involved.

RESULTS

Ictal onset time at sphenoidal and scalp recordings: initial ictal changes appeared simultaneously in scalp and sphenoidal recordings in 123 seizures (39.2%). Initial changes occurred earlier in sphenoidal recordings in 63 seizures (20.1%), whereas they were seen earlier on the scalp in 76 seizures (24.2%). Artefacts prevented the comparison between sphenoidal and scalp recordings in 16 seizures (5.1%) and no ictal changes were seen on the scalp and/or sphenoidal recordings in 36 seizures (11.5%). In most of the 63 seizures where ictal changes appeared earlier in sphenoidal recordings, a delayed ipsilateral scalp onset was seen as the signal amplitude increased or scalp changes could be identified retrospectively on the scalp with an onset which appeared simultaneous and ipsilateral to the initial sphenoidal changes. Sphenoidal recordings supplied additional information when compared to scalp recordings in only 22 seizures (7%): in 5 seizures with artefacts on the scalp, in 6 seizures with no changes on the scalp and in 11 seizures with discrepant laterality at onset. Congruence in laterality with respect to deep intracraneal FO recordings: of the 61 seizures with unilateral onset on the scalp, onsets at sphenoidal recordings and deep FO electrodes were ipsilateral in most cases. In only 3 of these 61 seizures (4.9%), sphenoidal recordings lateralized ipsilateral to the deep FO electrodes in the presence of a contralateral onset on the scalp. In 14 among the 122 seizures (11.5%) with bilateral asymmetrical onset on the scalp, sphenoidal recordings lateralized seizure onset ipsilateral to the deep FO electrodes in the presence of a contralateral scalp onset. Thus, when compared with scalp EEG, sphenoidal recordings increased laterality congruence with respect to deep FO electrodes in 17 seizures (5.4%).

CONCLUSIONS

Extracranial electrodes located next to the FO at the sphenoidal electrode site yield an improvement over suitable surface electrodes in the identification of ictal onset in only 5.4-7% of seizures. Such improvement derives from the fact that the low amplitude signals often seen at seizure onset may show higher amplitude on sphenoidal than on scalp recordings.

N-Acetylaspartate and creatine levels measured by (1)H MRS relate to recognition memory

OBJECTIVES

To investigate the relationship between recognition memory and metabolite levels in medial structures of the temporal lobes in the living human brain.

METHODS

Proton MRS ((1)H MRS) and the intracarotid amobarbital test were performed in 16 epileptic patients found suitable for temporal lobectomy. All patients had mesial temporal sclerosis. Metabolite ratios between N:-acetylaspartate (NAA), creatine and phosphocreatine (Cr + PCr), and choline-containing compounds (Cho) [NAA/(Cr + PCr), NAA/Cho, and NAA/(Cr + PCr + Cho)] were calculated for (1)H MRS voxels that included the amygdala, anterior half of the hippocampus, and underlying subiculum. Metabolite ratios were correlated with unilateral memory scores estimated by the intracarotid amobarbital test for words, objects, faces, and total score.

RESULTS

The total memory score, memory for objects and faces, and NAA/(Cr + PCr) were significantly lower for the hemisphere ipsilateral to the resection. The asymmetry indexes for NAA/(Cr + PCr) correlated with asymmetry indexes for words (rho = 0.82, p = 0.0001) and total memory (rho = 0. 72, p = 0.002). Analysis of memory scores and metabolite ratios from all 32 hemispheres revealed a correlation between NAA/(Cr + PCr) and memory for words (rho = 0.45, p = 0.009). A correlation between memory for words and NAA/(Cr + PCr) existed in the contralateral (rho = 0.58, p = 0.019) and in the right (rho = 0.51, p = 0.045) hemispheres, and a trend was found in the left hemispheres (rho = 0. 48, p = 0.06).

CONCLUSION

There is a correlation between memory for words and the NAA/(Cr + PCr) ratio from medial temporal structures in patients with mesial temporal sclerosis. The findings suggest that medial temporal structures and adjacent neocortex play a significant role in recognition memory in humans, particularly for words.

Failed surgery for epilepsy. A study of persistence and recurrence of seizures following temporal resection

From a series of 282 consecutive temporal resections for medically intractable epilepsy associated with mesial temporal sclerosis (MTS), dysembryoplastic neuroepithelial tumour (DNT) or non-specific pathology (NSP), 51 patients had persistent or recurrent seizures occurring at least monthly. Of these patients, 44 underwent detailed assessment of their postoperative seizures, which included clinical evaluation, interictal and ictal EEG and high-resolution MRI. Of the 20 patients with MTS in the original pathology, 14 (70%) had postoperative seizures arising in the hemisphere of the resection, the majority (12 patients) in the temporal region. Although MRI demonstrated residual hippocampus in five of these 12 patients, only one patient was considered to have seizures arising there, whilst the remainder had electroclinical evidence of seizure onset in the neocortex. In contrast, five of the MTS relapses (25%) had seizure onset exclusively in the contralateral temporal region. Among the 14 patients with non-specific pathology, relapse was also predominantly from the ipsilateral hemisphere (64%), but more relapsed from extratemporal sites compared with the MTS cases, including two with NSP who had occipital structural abnormalities. Although 70% of the 10 patients with DNT had postoperative partial seizures arising in the ipsilateral hemisphere, many (60%) had evidence of a more diffuse disorder with additional generalized seizures, cognitive and behavioural disturbance and multifocal and generalized EEG abnormalities. Nine patients (20%) had immediate postoperative seizure-free periods of at least 1 year, and seven of these had MTS in the operative specimen. Of these seven patients, four had ipsilateral temporal seizures and three had contralateral temporal seizures. Overall, few missed lesions were discovered on postoperative MRI and reoperations were performed or considered possible in a minority of cases. Despite well-defined preoperative electroclinical syndromes of temporal lobe epilepsy, many patients relapsed unexpectedly, either immediately or remotely from the time of surgery. Maturing epileptogenicity in a surgical scar was not, however, considered to be a significant primary mechanism in patients who relapsed after a seizure-free interval.

Sources of error in comparing functional magnetic resonance imaging and invasive electrophysiological recordings

OBJECT

Several authors have recently reported studies in which they aim to validate functional magnetic resonance (fMR) imaging against the accepted gold standard of invasive electrophysiological monitoring. The authors have conducted a similar study, and in this paper they identify and quantify two characteristics of these data that can make such a comparison problematic.

METHODS

Eight patients in whom surgery for epilepsy was performed and five healthy volunteers underwent fMR imaging to localize the part of the sensorimotor cortex responsible for hand movement. In the patient group subdural electrode mats were subsequently implanted to identify eloquent regions of the brain and the epileptogenic zone. The fMR imaging data were processed to correct for motion during the study and then registered with a postimplantation computerized tomography (CT) scan on which the electrodes were visible. The motion during imaging in the two groups studied, and the deformation of the brain between the preoperative images and postoperative scans were measured. The patients who underwent epilepsy surgery moved significantly more during fMR imaging experiments than healthy volunteers performing the same motor task. This motion had a particularly increased out-of-plane component and was significantly more correlated with the stimulus than in the volunteers. This motion was especially increased when the patients were performing a task on the side affected by the lesion. The additional motion is hard to correct and substantially degrades the quality of the resulting fMR images, making it a much less reliable technique for use in these patients than in others. Also, the authors found that after electrode implantation, the brain surface can shift more than 10 mm relative to the skull compared with its preoperative location, substantially degrading the accuracy of the comparison of electrophysiological measurements made in the deformed brain and fMR studies obtained preoperatively.

CONCLUSIONS

These two findings indicate that studies of this sort are currently of limited use for validating fMR imaging and should be interpreted with care. Additional image analysis research is necessary to solve the problems caused by patients' motion and brain deformation.

Significance of interictal bilateral temporal hypometabolism in temporal lobe epilepsy

OBJECTIVE

To assess the clinical implications and the pathophysiologic determinants of interictal bitemporal hypometabolism (BTH) in temporal lobe epilepsy (TLE) not associated with bilateral MRI abnormalities or intracranial space-occupying lesions.

METHODS

The authors compared the clinical, interictal, and ictal EEG, Wada test, and neuropsychology data of 15 patients with intractable complex partial seizures of temporal lobe origin and BTH with those of 13 consecutive patients with unilateral TLE associated with unilateral temporal hypometabolism (UTH) who remained seizure free for more than 3 years after anterior temporal lobectomy. 18F-fluorodeoxyglucose PET scans were analyzed visually and semiquantitatively, and ratios of counts in individual temporal areas to the rest of the cerebrum were compared with the corresponding values from 11 normal control subjects and with the nonepileptogenic hemisphere of the 13 patients with UTH. BTH was defined as more than 2.5 SDs below control values for two or more temporal areas on each side irrespective of any asymmetry.

RESULTS

BTH reflected bilateral independent seizure onset in eight patients (53%). The topography of the metabolic depression was not a reliable predictor of epileptogenicity, but involvement of the inferior temporal gyrus was related specifically to ipsilateral seizure onset (70% sensitivity, 100% specificity). In patients with unilateral TLE, contralateral hypometabolism was associated with longer disease duration and worst memory performance during the Wada test, which amounted to global amnesia after ipsilateral injection in three patients, precluding surgical treatment. Contralateral seizure spread in the ictal EEG was significantly faster in patients with BTH.

CONCLUSIONS

In TLE, symmetric or asymmetric BTH may signal bilateral independent seizure onset in approximately half the patients, especially when involving the inferior temporal gyrus. Alternatively, it may reflect an advanced stage of the disease process, characterized by a breakdown of the inhibitory mechanisms in the contralateral hemisphere, and secondary memory deficit associated with higher risk of postoperative memory decline. Patients with TLE and BTH but without bilateral MRI changes may still be operated on successfully, but surgical suitability should be proved by comprehensive intracranial EEG studies and Wada test.

Thalamic changes with mesial temporal sclerosis: MRI

We reviewed the preoperative images of 28 patients with pathologically proven mesial temporal sclerosis, to assess thalamic asymmetry and signal change. A further 25 nonsurgical patients with temporal lobe epilepsy and unequivocal, unilateral changes of mesial temporal sclerosis, and 20 controls, were also reviewed. None of the control group had unequivocal asymmetry of the thalamus. There was an ipsilateral asymmetrically small thalamus in five (18%) of the surgical group and in three (12%) of the nonsurgical patients. In four cases there was thalamic signal change. In three patients with thalamic volume loss there was ipsilateral hemiatrophy. All patients with an asymmetrically small thalamus had an asymmetrically small fornix and all but one a small ipsilateral mamillary body.

Probabilistic learning and reversal deficits in patients with Parkinson's disease or frontal or temporal lobe lesions: possible adverse effects of dopaminergic medication

Three groups of patients with Parkinson's disease (PD) - mild, unmedicated (UPD), mild, medicated (MPD) and severe, medicated (SPD) - and patients with lesions of the frontal lobe (FLL) or temporal lobe (TLL) were compared with matched controls on the learning and reversal of probabilistic and two-pair concurrent colour discriminations. Both of the cortical lesion groups showed reversal deficits, with no increase in perseverative responding. The UPD group, although impaired on a spatial recognition task, showed intact discrimination learning and reversal; the MPD and SPD patients showed non-perseverative reversal impairments on both reversal tasks. Two hypotheses - based on disease severity and possible deleterious effects of medication - are offered to explain the reversal impairments of the PD patients and the results are discussed in terms of the role of dopamine in reward-based learning.

A study of mortality after temporal lobe epilepsy surgery

OBJECTIVE

To determine early and late mortality in a cohort of 305 consecutive patients who had temporal lobe epilepsy (TLE) surgery over a 20-year period.

METHODS

Survival status, cause of death, and postoperative clinical details of those who died were ascertained in a cohort of 305 patients who had TLE surgery. Mortality was related to postoperative seizure status, operative pathology, and side of resection.

RESULTS

The survival status of 299 patients was established. Twenty deaths occurred. Mortality was 1 per 136 person-years, with a standardized mortality ratio (SMR) of 4.5 (95% confidence interval [CI], 3.2 to 6.6). Six deaths were sudden and unexpected (SUDEP). The SUDEP rate was 1 per 455 person-years. The overall death and SUDEP rates were lower than those reported for similar patient populations with chronic epilepsy. Mortality in patients who had right-sided resections for mesial temporal sclerosis (MTS) remained considerably elevated with a mortality rate of 1 per 54 person-years, an SMR of 32.0 (95% CI, 24.7 to 40.5), and a SUDEP rate of 1 per 134 person-years. These patients had significantly lower seizure remission rates than left-sided patients, but the excess mortality was not simply explained by those patients whose partial seizures were uninfluenced by surgery. Patients who died had more severe or convulsive seizures despite an overall reduction in seizure frequency.

CONCLUSIONS

The present findings confirm previous reports that TLE surgery lowers but does not normalize the overall mortality associated with chronic epilepsy. In patients with right-sided MTS, however, the postoperative mortality has remained similar to other groups with medically intractable seizures.

Hippocampal involvement in spatial and working memory: a structural MRI analysis of patients with unilateral mesial temporal lobe sclerosis

Forty-seven patients with unilateral temporal lobe epilepsy (TLE) were investigated on the Nine-Box Maze. The task was designed to compare working memory and spatial mapping theories of the functions of the hippocampus and provide measures of spatial, object, working, and reference memory. The results extended our previous findings in a larger group of patients. Spatial memory deficits across both working and reference memory conditions were found in patients with a right epileptogenic focus. There was no evidence of an object working memory deficit, but a nonlateralized impairment in object reference memory was revealed, which is consistent with our previous findings. The pattern of results was confirmed in a subgroup of 33 patients with unilateral atrophy localized to the hippocampus and parahippocampal gyrus, as verified by volumetric analysis of magnetic resonance images. In addition spatial memory errors significantly correlated with volumetric measures of mesial temporal lobe structures and not with measures of the remaining temporal cortex. In contrast, object reference memory errors correlated with volumetric measures of the temporal cortex and not with mesial temporal lobe structures. These findings support a specialized role for the right hippocampal region in spatial memory.

Coexistence of temporal lobe and idiopathic generalized epilepsies

OBJECTIVE

To assess the interrelation of idiopathic generalized epilepsy (IGE) and temporal lobe epilepsy (TLE) when they coexist in the same patient.

METHODS

The authors reviewed the electroclinical features of 350 consecutive patients who had temporal resection between 1975 and 1997 at the Maudsley and King's College Hospitals, London.

RESULTS

Two patients had the unusual combination of TLE and IGE (0.57%). In the first, the clinical onset of juvenile myoclonic epilepsy followed the surgical resolution of his partial seizures but had been heralded for at least 5 years by subclinical spontaneous and photically induced generalized spike-wave discharges. In the second, TLE and juvenile absence epilepsy had a long parallel course before surgery. After surgery he had no further partial seizures.

CONCLUSION

These cases suggest that when an idiopathic absence or myoclonic syndrome manifests in a patient with symptomatic TLE, the phenotype may not be a merged syndrome. Rather, the two conditions can retain their inherent electroclinical profile, responsiveness to treatment, and prognosis.

Interictal 18FDG PET findings in temporal lobe epilepsy with déjà vu

The authors studied the functional anatomy of the déjà vu (DV) experience in nonlesional temporal lobe epilepsy (TLE), using interictal fluorine-18 fluorodeoxyglucose PET in 14 patients with and 17 patients without DV. Several clinical conditions, such as age at PET study, side of ictal onset zone, and dominance for language, were no different between the two groups. The patients with DV showed significant relative reductions in glucose metabolism in the mesial temporal structures and the parietal cortex. The findings demonstrate that ictal DV is of no lateralizing value. They further suggest that temporal lobe dysfunction is necessary but not sufficient for the generation of DV. Extensive association cortical areas may be involved as part of the network that integrates this distinct experience.

Generation of scalp discharges in temporal lobe epilepsy as suggested by intraoperative electrocorticographic recordings

OBJECTIVES

To study the variability, topography, polarity, duration, and incidence of interictal epileptiform discharges (EDs) in the scalp EEG and electrocorticogram (ECoG) from 16 patients with temporal lobe epilepsy who underwent surgical treatment.

METHODS

Preoperative scalp EEGs during quinalbarbitone induced sleep were compared with preresection ECoGs obtained under general anaesthesia. The analysis was based on the initial ECoG record obtained before activation by intravenous thiopentone, and the EEG during stages I and II of sleep.

RESULTS

On the scalp, 15 patients had a single discharge pattern, spikes were predominantly negative, EDs were of largest amplitude at the anterior temporal electrode in 13 patients and mean discharge incidence was 4.0 (SD 4.2) discharges/min. In ECoG recordings, nine patients had two independent ECoG patterns, the polarity of spikes was negative, positive-negative, or positive, the site of maximal amplitude varied greatly between subjects, discharge incidence was 7.3 (SD 3.9) discharges/min. There was no relation between the topography of the largest spikes on the scalp and in the ECoG. In 14 patients, scalp spikes showed statistically significant longer duration on the scalp than in the ECoG. In seven patients who had frequent widespread ECoG discharges, averaging spikes across ECoG channels generated spiky patterns of duration similar to that of scalp spikes.

CONCLUSION

It seems that, in temporal lobe epilepsy, scalp discharges originate from widespread ECoG discharges and tend to produce a stereotyped pattern on the scalp with largest amplitudes at the anterior temporal electrodes. This is probably due to local anatomical peculiarities in the brain coverings, such as skull discontinuities, rather than to the location of neuronal generators within the temporal lobe. Due to spatiotemporal averaging, widespread cortical discharges which become asynchronous during propagation appear with increased duration and blunted waveform in the EEG, whereas sharply localised phenomena such as positive focal spikes are not recorded from the scalp.

Comparison of sphenoidal, foramen ovale and anterior temporal placements for detecting interictal epileptiform discharges in presurgical assessment for temporal lobe epilepsy

OBJECTIVES

Some authors have recently stressed that the position of the tip of the sphenoidal electrode plays a crucial role in its efficacy to detect mesio-basal spikes. We have tested this hypothesis by comparing the sensitivity of a contact of a foramen ovale bundle located at the foramen ovale (CFO) with scalp electrodes in detecting interictal epileptiform discharges. We have also compared deep and superficial foramen ovale contacts in the same bundle in order to establish whether deeper contacts can detect epileptiform discharges not seen at the foramen ovale or on the scalp.

METHODS

The sensitivity for detecting epileptiform discharges of simultaneous intracranial and scalp EEG recordings from 20 patients under telemetric presurgical assessment for temporal lobe epilepsy were compared.

RESULTS

Out of 2280 epileptiform discharges evaluated, about 70% were seen only at the deep foramen ovale contacts. Out of the 722 discharges recorded by CFO and/or scalp electrodes, 698 were seen at the CFO and 690 at the scalp anterior temporal electrode. Only on 29 occasions (4.15%) were discharges recorded at the CFO and not at the anterior temporal electrode. On 21 occasions (3.04%) CFO failed to detect discharges seen at the anterior temporal electrode.

CONCLUSIONS

Our findings confirm previous results suggesting that sphenoidal electrodes, however accurately positioned, offer no significant increase in detection sensitivity compared with anterior temporal scalp electrodes. In addition, these results confirm that a large proportion of discharges seen at the deepest foramen ovale contacts are not seen either on the scalp nor at the superficial foramen ovale contacts.