Extent of resection in temporal lobectomy for epilepsy. I. Interobserver analysis and correlation with seizure outcome

Mesial atrophy and outcome after amygdalohippocampectomy or temporal lobe removal

We studied 74 consecutive patients with temporal lobe epilepsy who were treated surgically and in whom the volumes of mesial temporal structures were determined preoperatively by magnetic resonance imaging. We divided the patients into three groups according to the volumetric findings: unilateral (63.5% of the patients), bilateral (23%), or no atrophy (13.5%) of the amygdala-hippocampal formation. Two distinct surgical approaches were used: selective amygdalohippocampectomy (n = 37) or anterior temporal lobe resection (n = 37). Outcome was assessed at least 1 year after surgery, according to Engel's modified classification. Patients with unilateral mesial temporal atrophy had significantly better results compared with the other two groups (p < 0.001): We found excellent results (class I or II outcome) in 93.6% of the patients with unilateral atrophy, in 61.7% of those with bilateral atrophy, and in 50% of the group with no significant atrophy of mesial temporal structures. The two different surgical techniques were equally effective, regardless of the pattern of atrophy. In conclusion, magnetic resonance volumetric studies in temporal lobe epilepsy proved to be an important preoperative prognostic tool for surgical treatment, but they did not provide guidance for selecting one surgical approach compared to the other.

Extent of medial temporal resection on outcome from anterior temporal lobectomy: a randomized prospective study

WE REPORT A prospective, randomized, blinded clinical trial comparing seizure and neuropsychological outcomes from anterior temporal lobectomies between two groups of patients. One group (n = 34) underwent hippocampal resection posteriorly to the anterior edge of the cerebral peduncle (partial hippocampectomy). In the other group (n = 36), the hippocampus was removed further to the level of the superior colliculus (total hippocampectomy). The amount of lateral cortical resection was the same between groups. Patients were and neuropsychological morbidity. At 1 year postoperatively, the total hippocampectomy group had a statistically superior seizure outcome compared with the partial hippocampectomy group (69 versus 38% seizure-free), and examination of time to first seizure (survival analysis) revealed significantly superior outcomes associated with total hippocampectomy. There was no increased neuropsychological morbidity associated with the more extensive hippocampal resection.

Seizure control and extent of mesial temporal resection

Controversy exists about the extent of mesial temporal lobe resection that improves seizure control in patients with temporal lobe epilepsy. In this retrospective study, 70 patients with mesial temporal seizure activity (without evidence of tumor or vascular malformation) were surgically treated and followed for at least 2 years. The extent of mesial temporal resection was based on the findings of interictal and ictal discharges using depth electrodes, which were inserted preoperatively or intraoperatively by the orthogonal approach to the amygdaloid and hippocampal regions. Only the amygdala was resected along with the limited lateral neocortex if no epileptiform activity involved the hippocampus. The amount of hippocampal excision was determined by the extent of interictal seizure activity. The following groups became seizure free: all 8 patients with only amygdalar resection; 6 of 10 patients with amygdalar and < or = 1 cm hippocampal resection; 23 of 38 with 1-2 cm hippocampal removal, and 11 of 14 with > 2 cm hippocampal excision. In cases where there was no hippocampal resection, neuropsychological outcome compared favorably with controls. Our results suggest that although most patients with temporal lobe epilepsy require hippocampal resection of varying degrees, there is a subset in whom the amygdala may be the crucial element of a mesial temporal epileptogenic network. These patients can undergo a surgical resection sparing the hippocampus without compromising seizure outcome.

Frameless stereotaxy for surgery of the epilepsies: preliminary experience. Technical note

Frameless stereotactic techniques used in conjunction with three-dimensional images allow accurate planning and performance of a variety of neurosurgical procedures. The authors have used the frameless stereotactic Allegro Viewing Wand system to provide real-time correlation of the operating field and computerized images in 42 neurosurgical operations, including 31 epilepsy procedures. The system consists of an image-processing computer that creates three-dimensional and triplanar images; a mobile computer to display reformatted magnetic resonance images; and a hand-guided, articulated, position-sensing arm with a probe. At the start of the operation, the probe identifies the patient's facial and scalp features and correlates these with the computerized images. The position-sensing arm can then guide the operation and locate anatomical structures and lesions of interest. This system can be used to advantage in performing smaller craniotomies and intraoperatively locating anatomical structures and lesions to be removed. Postoperative magnetic resonance images demonstrate that this technique was accurate to within 3 mm in measuring the anteroposterior resection of fixed structures, such as hippocampus and corpus callosum. Disadvantages include longer preoperative preparation for data analysis and lack of both real-time computer analysis of tissue removal and angiographic data display. Preliminary experience suggests that the viewing wand system's advantages outweigh the disadvantages, and it is most helpful as an adjunctive navigational device in the microsurgical treatment of epilepsy.

Image guided audit of surgery for temporal lobe epilepsy

Studies on surgery for temporal lobe epilepsy are hampered by lack of information about the actual surgery that has taken place. A method is described for accurately measuring the volumes of resection by MRI after surgery. Ten cases of surgically treated temporal lobe epilepsy (nine non-tailored resections, one selective amygdalohippocampectomy) are presented to show the technique. Indices of extent of resection in both the mesiobasal and lateral temporal lobe compartments have been measured, compared, and evaluated. By comparison with identical preoperative volumetric MRI the hippocampal resections have been correlated with the demonstrated hippocampal volume loss, thought to be of relevance in the aetiology of temporal lobe epilepsy. Detailed postoperative audit in this manner is vital in providing a rational basis for follow up studies of outcome.

Serial cognitive testing in temporal lobe epilepsy: longitudinal changes with medical and surgical therapies

Cognitive testing was repeated at intervals ranging from 1 to 8 years in 47 adult patients with temporal lobe epilepsy (TLE). Each patient underwent standardized batteries, including the Wechsler Adult Intelligence Scale, Revised (WAIS-R), and Wechsler Memory Scale (WMS). Both surgically treated and nonsurgical patients were examined. The nonsurgical group underwent serial testing for clinical indications, usually for complaints of memory dysfunction. Longitudinal testing could not verify any mean deterioration of intellect or memory in this group; variance over time was similar to test-retest norms in healthy controls. WAIS-R scores before and after resection in the surgical group were similar to our serial WAIS-R data in nonsurgical patients. When we divided surgical patients according to side of epileptogenesis, we noted the expected differences in verbal and visual memory. Right-sided surgery patients improved significantly in Full-Scale IQ (FSIQ) and tended to improve in logical memory on postoperative testing. Patients undergoing left resections had no retest improvement and tended to show decrease in several measures of verbal memory. Our findings should stimulate continued investigation into the natural history of lateralized memory and intellectual function in epilepsy, particularly to clarify long-term cognitive outcome in nonsurgical patients.

Predictive factors for success in surgical treatment for partial epilepsy: a multivariate analysis

We conducted a longitudinal self-controlled study of 131 patients aged 4-60 treated with resective surgery for medically uncontrolled partial epilepsy from 1949 to 1988. Using multivariate logistic regression, we showed that pre- and perioperative variables can be used to predict "success" or "failure" of surgical resective treatment in approximately 79% of cases. If the predicted probability is > 0.75 or < 0.25, the model predicts a correct result in 87% of cases. Eight predictive factors emerged with a backward multivariate logistic regression model with the likelihood-ratio (LR) test to exclude variables from the equation: (a) the influence of the surgical team and surgical procedure, (b) the presence of paresis preoperatively, (c) duration of disease, (d) age at treatment, (e) positive neuroradiologic findings in preoperative investigations, (f) preoperative complex partial seizures (CPS), (g) nonepileptic EEG abnormalities, and (h) generalized spike activity in EEG preoperatively. Sex, age at first seizure, area of resection, presence of simple or generalized seizures preoperatively, preoperative seizure frequency, tissue pathology, use of computed tomography/nuclear magnetic resonance (CT/NMR) in preoperative investigations, degree of preoperative neurologic deficit, perioperative electrocorticographic results, and bilateral EEG spikes did not have predictive value in the model.

Volumetric analysis of epilepsy surgery resections using high resolution magnetic imaging: technical report

A method is described for accurately measuring the volume and site of epilepsy surgery resections utilizing magnetic resonance imaging. Accuracy has been assessed using post-mortem studies, and both the intra- and interobserver variability is consistently less than 5%. The technique has so far been applied to 25 patients following a variety of operations for medically intractable epilepsy. It provides the crucially accurate baseline required for meaningful follow-up outcome studies of epilepsy surgery. Consequently, it should allow the development of more precise prognostic indices for such operations.

Temporal lobectomy for uncontrolled seizures: the role of positron emission tomography

We evaluated the role of positron emission tomography (PET) with [18F]deoxyglucose (FDG) (FDG-PET) for planning surgery in 53 patients who had temporal lobectomy for uncontrolled seizures at National Institutes of Health from 1981 to 1990. Investigators blinded to PET data used results of telemetered video-electroencephalographic ictal monitoring and other standard criteria to decide whether subdural electrodes (22 patients, i.e., the "invasive" group) should be implanted or surgery performed. PET scans were analyzed using a standard regional template. Mean lateral but not mesial temporal asymmetry was significantly higher in patients who became seizure free (p < 0.03). Patients with > or = 15% hypometabolism were significantly more likely to be seizure free in the entire study population and the invasive subgroup. Visual identification of hypometabolism was less accurate. When a clear temporal ictal surface electroencephalographic focus was present, FDG-PET provided less additional information. FDG-PET may be particularly valuable if the surface electroencephalographic scan is nonlocalizing. In addition to helping to identify the seizure focus, it may allow limitation of invasive electrode placement to those necessary for functional mapping. When PET is used to identify epileptic foci, quantitative measurements of asymmetry should be made.

A longitudinal assessment of seizure outcome and overall benefit from 100 cortectomies for epilepsy

Results of 100 cortical resections for 76 temporal, 23 frontal and one parietal lobe epilepsies were studied in terms of seizure relief and overall benefit. A non-homogenous Markov chain model was used to take into account both the intravariability of post-surgical outcome and the differences in duration of follow-up in a group of patients consecutively operated. The seizure free (SF) state was defined as no seizure in the previous five months at first follow up visit and none in the preceding 12 months at subsequent annual visits. For the whole of the population the SF probability was 82%, 66%, 61%, and 62% at six months, one year, two and five years respectively. A better outcome was found for temporal lobe epilepsy (SF probability: 68% at the fifth postoperative year) than for frontal lobe epilepsy (SF probability: 42% at the fifth postoperative year) with a statistically significant difference. Pre- and postoperative interictal signs and symptoms were classified according to their clinical significance: (a) mild handicap--symptoms recognisable but no interference with usual life, and (b) moderate or severe handicap--interference with some or all daily activities. The interictal state was considered more impaired after surgery than before in two situations: (a) either symptoms, absent before surgery, appeared in the postoperative period involving a moderate or severe handicap, or (b) symptoms present before surgery and answerable for a mild or moderate handicap that increased to involve a moderate or severe handicap respectively in the postoperative period. Surgery was considered a major benefit when two conditions were fulfilled-namely, a SF state and no deterioration of the interictal stage when compared with the preoperative period. The probability of obtaining such a benefit was 58%, 51%, 48% and 56% at six months, one year, two and five years respectively. The results suggest that surgery is an effective treatment for more than 50% of long lasting medically intractable epilepsies.

Mesial temporal subdural electrode as a substitute for depth electrode

As a substitute for depth electrodes, mesial temporal subdural electrodes were devised. This electrode has a slender trapezoid shape and is easily introduced to the inner uppermost portion of the parahippocampal gyrus. Our results have shown that mesial temporal electrodes can detect not only interictal spikes but also subclinical and clinical seizure discharges from the mesiolimbic structures, and they have excellent capability for lateralization of the mesial temporal epileptic focus. If mesial temporal subdural strips are used in combination with lateral temporal subdural grids, comprehensive understanding of the focus distribution throughout the temporal lobes will be possible without using depth electrodes.

Seizure outcome following standard temporal lobectomy: correlation with hippocampal neuron loss and extrahippocampal pathology

The authors reviewed 149 patients who underwent standard anterior temporal lobectomies for intractable complex partial epilepsy with a mean follow-up period of 5 years. Quantitative analyses of hippocampal neuron loss showed that all patients had some cell loss compared to control hippocampi obtained at autopsy. The average hippocampal cell loss was categorized as severe (greater than 30% of autopsy control levels) or mild. Analysis of hippocampal and extrahippocampal pathologies showed that in 109 cases (73%, the hippocampal lesion group) hippocampal cell loss was mild in 17 cases (16%) and severe in 92 cases (84%); in the remaining 40 cases (27%, the extrahippocampal structural lesion group) hippocampal cell loss was mild in 24 cases (60%) and severe in 16 (40%). The first index of surgical outcome was worthwhile seizure reduction, which occurred in 94 cases (86%) with mild or severe hippocampal lesions and in 33 cases (82%) with extrahippocampal pathology. In the hippocampal lesion group, worthwhile seizure reduction occurred in 90% of cases with severe and in only 65% of cases with mild hippocampal cell loss (p = 0.015). In the extrahippocampal pathology group, worthwhile seizure was not statistically different, whether hippocampal cell loss was severe (94% of cases) or mild (75% of cases). The second index of surgical outcome was the occurrence of residual seizures in the patients with worthwhile seizure reduction, which would indicate remaining epileptogenic tissue. In the hippocampal lesion group, the incidence of residual seizures was not statistically different whether hippocampal cell loss was severe (24% of cases) or mild (45% of cases). However, in the extrahippocampal pathology group, residual seizures occurred in 53% of cases with severe cell loss (dual pathology) but in only 11% of cases with mild cell loss (p = 0.025). Worthwhile seizure reduction can be predicted by the presence of either severe hippocampal cell loss or an extrahippocampal structural lesion. However, residual seizures more frequently follow in cases with a combination of both (extrahippocampal pathology associated with severe hippocampal cell loss, or dual pathology), suggesting that epileptogenic tissue more likely extends outside the boundaries of a standard temporal lobectomy.

Intracarotid amobarbital procedure: I. Prediction of decreased modality-specific memory scores after temporal lobectomy

To assess predictive value of the intracarotid amobarbital procedure (IAP) for decreased postoperative modality-specific memory, we studied 37 temporal lobectomy patients with intractable partial epilepsy who were selected for operation independent of preoperative IAP findings. When ipsilateral IAP failure was defined by an absolute method as a retention score less than 67%, the results were not associated with decreased modality-specific memory after operation. When ipsilateral IAP failure was defined by a comparative method as a retention score at least 20% lower after ipsilateral than contralateral injection, the results showed greater differences between groups, but differences still did not achieve statistical significance. Four left-resection patients who failed the ipsilateral IAP had a median postoperative change in the Wechsler Memory Scale-Revised (WMS-R) Verbal Memory Index score of -14%, whereas 16 left-resection patients who passed the ipsilateral IAP had a mean postoperative change in the WMS-R Verbal Memory Index score of -7.5% (p = 0.12). These results suggested that the IAP interpreted comparatively may be a helpful adjunctive test in assessment of relative risk for modality-specific memory dysfunction after temporal lobectomy, but larger series of operated patients are needed to confirm this possibility. In this series, complete amnesia was not noted after ipsilateral injection, even in patients with postoperative modality-specific memory decline.

Natural history of recurrent seizures after resective surgery for epilepsy

Seizures persist or recur in 20-60% of patients after resective surgery for intractable partial epilepsy. Further information about the natural course of these seizures is lacking in the literature. During one decade of epilepsy surgery at a single institution, we identified 72 patients with recurrent postoperative seizures after resective procedures for epilepsy. Prospectively compiled seizure diaries, hospital records, and outpatient office records were reviewed and supplemented by telephone communications to assess subsequent seizure frequency. Follow-up data was available ranging from 6 months to 7 years 5 months (mean 3 years 5 months). The likelihood of persistent seizures and recurrent intractability was examined with life-tables. Seizures recurred within the first postoperative year in 86% of patients and were similar to preoperative events in 74% of patients. After the first seizure recurrence, there was 80% likelihood of persistent seizures in the next 6 years and 40% likelihood of intractability (more than one seizure a month despite optimal medical therapy). The interval until recurrence within the first postoperative year did not affect the likelihood of subsequent seizures or intractability. Late seizure recurrence (after the first year) was not associated with any instances of subsequent intractability. Recurrent seizures after extratemporal resections were more likely to become persistent and intractable than seizures recurring after temporal resections. This information provides rational prognostication and assists in counseling patients with recurrent seizures after resective surgery for intractable epilepsy.

Imaging techniques in the localization of epileptiform abnormalities

The success of surgical intervention in the partial epilepsies is crucially affected by the accuracy of pre- and intraoperative source location techniques. Several approaches to the localization problem have been employed, that with the longest history being scalp-recorded EEG. Despite considerable advances in other imaging technologies such as MRI and PET, localization via the electrical signals generated by epileptic brain continues to provide the data most relied upon in pre-operative assessment. The present paper presents an overview of the contribution of various localization techniques. It is argued that electrical signals of the brain, as represented by EEG and MEG, remain the best methods to locate sources, and that the application of analysis techniques presently under investigation will further improve the accuracy of the non-invasive scalp-EEG approach.

Normal P300 following extensive damage to the left medial temporal lobe

Event-related potentials (ERPs) were recorded during auditory and visual "oddball" tasks from a patient with a severe verbal memory deficit due to a low grade infiltrating glioma which involved the full extent of the left medial temporal lobe. In both sensory modalities, the patient's oddball-evoked P300s were symmetrical and of normal amplitude. These findings are difficult to reconcile with the hypothesis that the hippocampus, or any other medial temporal structure, makes a substantial contribution to the scalp P300.

Relationship of hippocampus and amygdala to coronal MRI landmarks

Magnetic resonance imaging is playing an increasingly important role in the evaluation of the hippocampus, particularly in epilepsy, schizophrenia, and Alzheimer's dementia. Because of the complex configuration of the hippocampus, it is difficult to compare from patient to patient. We developed a system to allow comparison of the hippocampus on coronal images. We performed 34 magnetic resonance studies on 29 normal subjects. Ten anatomic landmarks were identified. These landmarks have a consistent 5-mm periodicity regardless of usual head flexion. In the second phase of our investigation, we showed that the amygdala, hippocampal head, hippocampal body, and hippocampal tail have a consistent relationship to the coronal magnetic resonance imaging landmarks.

Extent of resection in temporal lobectomy for epilepsy. II. Memory changes and neurologic complications

We present correlations of extent of temporal lobectomy for intractable epilepsy with postoperative memory changes (20 cases) and abnormalities of visual field and neurologic examination (45 cases). Postoperative magnetic resonance imaging (MRI) in the coronal plane was used to quantify anteroposterior extent of resection of various quadrants of the temporal lobe, using a 20-compartment model of that structure. The Wechsler Memory Scale-Revised (WMS-R) was administered preoperatively and postoperatively. Postoperative decrease in percentage of retention of verbal material correlated with extent of medial resection of left temporal lobe, whereas decrease in percentage of retention of visual material correlated with extent of medial resection of right temporal lobe. These correlations approached but did not reach statistical significance. Extent of resection correlated significantly with the presence of visual field defect on perimetry testing but not with severity, denseness, or congruity of the defect. There was no correlation between postoperative dysphasia and extent of resection in any quadrant. Assessment of extent of resection after temporal lobectomy allows a rational interpretation of postoperative neurologic deficits in light of functional anatomy of the temporal lobe.

Can sharp waves localized at the sphenoidal electrode accurately identify a mesio-temporal epileptogenic focus?

In our patient population that had undergone antero-temporal lobectomy, we found 20 patients with a unilateral sphenoidal/antero-temporal interictal focus. All patients had normal computed tomography (CT) scans. Invasive recordings with subdural electrode arrays placed over and under the temporal lobe were used in every patient. We found that the scalp interictal focus predicted for all patients that both the interictal sharp waves and ictal onset would be mesiobasal/anterotemporal in location on the subdural arrays. Seventy-five percent of these patients had an excellent outcome with temporal lobectomy.