Frontal Lobe Decortication (Frontal Lobectomy with Ventricular Preservation) in Epilepsy-Part 1: Anatomic Landmarks and Surgical Technique.

BACKGROUND: An extensive frontal resection is a frequently performed neurosurgical procedure, especially for treating brain tumor and refractory epilepsy. However, there is a paucity of reports available regarding its surgical anatomy and technique. OBJECTIVES: We sought to present the anatomic landmarks and surgical technique of the frontal lobe decortication (FLD) in epilepsy. The goals were to maximize the gray matter removal, spare primary and supplementary motor areas, and preserve the frontal horn. MATERIAL AND METHODS: The anatomic study was based on dissections performed in 15 formalin-fixed adult cadaveric heads. The clinical experience with 15 patients is summarized. RESULT: FLD consists of 5 steps: 1) coagulation and section of arterial branches of lateral surface; 2) paramedian subpial resection 3 cm ahead of the precentral sulcus to reach the genu of corpus callosum; 3) resection of gray matter of lateral surface, preserving the frontal horn; 4) removal of gray matter of basal surface preserving olfactory tract; 5) removal of gray matter of the medial surface under the rostrum of corpus callosum. The frontal horn was preserved in all 15 patients; 12 patients (80%) had no complications; 2 patients presented temporary hemiparesis; and 1 Rasmussen syndrome patient developed postoperative fever. The best seizure control was in cases with focal magnetic resonance imaging abnormalities limited to the frontal lobe. CONCLUSION: FLD is an anatomy-based surgical technique for extensive frontal lobe resection. It presents reliable anatomic landmarks, selective gray matter removal, preservation of frontal horn, and low complication rate in our series. It can be an alternative option to the classical frontal lobectomy.

[Transient charles bonnet syndrome after excision of a right occipital meningioma: a case report].

Charles Bonnet syndrome is a condition characterized by visual hallucinations. These simple or complex visual hallucinations are more common in elderly individuals with impaired peripheral vision. The current report describes a case of transient Charles Bonnet syndrome appearing after the removal of a meningioma. The patient was a 61-year-old man who already had impaired visual acuity due to diabetic retinopathy. Brain MRI revealed a cystic tumor severely compressing the right occipital lobe. Starting on day 2 postoperatively, the patient was troubled by recurring visual hallucinations involving people, flowers, pictures, and familiar settings(the train and a coffee shop). These continued for 3.5 months. This period roughly coincided with the time for the occipital lobe to recover from the compression caused by the tumor, a fact that was confirmed by several MRI scans. ¹²³I-IMP SPECT performed 1 month after the surgical operation showed an area of hypoperfusion in the right parieto-occipital lobe. Based on the patient's clinical course and MRI findings, the mechanism of onset of visual hallucinations in this patient was put forward. The release of pressure in the brain by tumor removal and subsequent recovery changed the blood flow to the brain. This triggered visual hallucinations in the patient, who was already predisposed to developing Charles Bonnet syndrome because of diabetic retinopathy. This case is interesting since it indicates that central neurological factors, as well as visual deficits, may induce the appearance of visual hallucinations in Charles Bonnet syndrome.

Practice parameter: temporal lobe and localized neocortical resections for epilepsy: report of the Quality Standards Subcommittee of the American Academy of Neurology, in association with the American Epilepsy Society and the American Association of Neurological Surgeons.

OBJECTIVES/METHODS: To examine evidence for effectiveness of anteromesial temporal lobe and localized neocortical resections for disabling complex partial seizures by systematic review and analysis of the literature since 1990. RESULTS: One intention-to-treat Class I randomized, controlled trial of surgery for mesial temporal lobe epilepsy found that 58% of patients randomized to be evaluated for surgical therapy (64% of those who received surgery) were free of disabling seizures and 10 to 15% were unimproved at the end of 1 year, compared with 8% free of disabling seizures in the group randomized to continued medical therapy. There was a significant improvement in quantitative quality-of-life scores and a trend toward better social function at the end of 1 year for patients in the surgical group, no surgical mortality, and infrequent morbidity. Twenty-four Class IV series of temporal lobe resections yielded essentially identical results. There are similar Class IV results for localized neocortical resections; no Class I or II studies are available. CONCLUSIONS: A single Class I study and 24 Class IV studies indicate that the benefits of anteromesial temporal lobe resection for disabling complex partial seizures is greater than continued treatment with antiepileptic drugs, and the risks are at least comparable. For patients who are compromised by such seizures, referral to an epilepsy surgery center should be strongly considered. Further studies are needed to determine if neocortical seizures benefit from surgery, and whether early surgical intervention should be the treatment of choice for certain surgically remediable epileptic syndromes.

Spatial localization after excision of human auditory cortex.

Neurophysiological and animal ablation studies concur that primary auditory cortex is necessary for computation of the spatial coordinates of a sound source. Human studies have reported conflicting findings but have often suffered from inadequate psychophysical measures and/or poor lesion localization. We tested patients with unilateral temporal lobe excisions either encroaching on or sparing Heschl's gyrus (HG), quantifying lesion extent using anatomical magnetic resonance imaging measures. Subjects performed two tasks. In the localization task, they heard single clicks in a free-field spatial array subtending 180 degrees of azimuth and indicated the perceived location with a laser pointer. In the discrimination task, two clicks were presented, and subjects indicated if they were in the same or different position. As a group, patients with right temporal excision, either encroaching onto HG or not, were significantly impaired in both hemifields in both tasks, although this was not true for all individuals. Patients with left temporal resections generally performed normally, although some of the patients with left HG excision showed impaired performance bilaterally, especially in the discrimination task. This pattern stands in marked contrast to previous studies showing significant preservation of localization in hemispherectomized patients. We conclude that (1) contrary to hypotheses derived from animal studies, human auditory spatial processes are dependent primarily on cortical areas within right superior temporal cortex, which encompass both spatial hemifields; (2) functional reorganization may not take place after restricted focal damage but only after more extensive early damage; and (3) the existence of individual differences likely illustrates differential patterns of functional lateralization and/or recovery.

Pattern electroretinograms after cerebral hemispherectomy.

Cortically blind patients with brain damage restricted to the optic radiations or primary visual cortex may be able to detect and discriminate visual stimuli presented in their field defects, even though they deny seeing them. In contrast, patients who are hemianopic as a result of cerebral hemispherectomy cannot explicitly discriminate visual stimuli in their field defects, even when forced choice procedures are used. A possible explanation for this difference is that retrograde, transneuronal degeneration of the retina, which affects approximately 85% of wavelength-sensitive ganglion cells (approximately 70% of the total) after damage restricted to striate cortex, could be far more extensive after hemispherectomy, rendering the retina incapable of processing and conveying visual information to the brain. To test this, we assessed retinal ganglion cell function by means of electroretinography in three patients with cerebral hemispherectomy who were functionally blind. Steady-state pattern electroretinograms elicited by achromatic and isoluminant-chromatic (red-green) sinusoidal gratings, whose contrast was temporally modulated, were recorded from both blind and sighted hemiretinae. The electroretinograms were qualitatively indistinguishable from those of a control patient with a unilateral striate cortical lesion with documented visual capacity in his field defect. Within-subject analysis of variance revealed significant differences in the amplitude of the second harmonic (2f(0)) component of the averaged signal (diagnostic of retinal ganglion cell function) with respect to stimulus, but no significant differences between blind and sighted hemiretinae. This indicates that many retinal ganglion cells must have survived in the hemispherectomized patients. Isoluminant chromatic stimuli tended to elicit stronger signals than achromatic stimuli, which was unexpected given that wavelength-opponent Pbeta ganglion cells are far more susceptible than broad-band Palpha ganglion cells to transneuronal degeneration after cortical damage. It suggests that the 2f(0) component of the response to isoluminant chromatic stimuli might not reflect the activity of chromatic processes. Overall, the results show that the absence of residual vision in the blind fields of patients with cerebral hemispherectomy cannot be due to complete degeneration of retinal ganglion cells and, by extension, complete degeneration of their subcortical targets. This supports an alternative explanation, which is that intact extrastriate cortex is required for mediating voluntary responses to visual stimuli presented in the scotoma.

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.

Retinal projections to the pregeniculate nucleus in the hemispherectomized monkey.

Intraocular injections of tritiated proline were used to test the hypothesis that unilateral removal of all visual cortical areas results in increased distribution of retinal terminals in the pregeniculate nucleus (PGN) of the thalamus in monkeys. Following hemispherectomy, retinal input to the ipsilateral PGN was reduced by an average of 18.5% when compared to its contralateral homologue, which corresponded to the reduction in nuclear volume (19.3%). Our results show that removal of cortical afferents to the external layer of the PGN does not induce invasion of retinal projections into this region of the nucleus.

Emotional cognition without awareness after unilateral temporal lobectomy in humans.

To investigate the function of the amygdala in human emotional cognition, we investigated the electrodermal activity (EDA) in response to masked (unseen) visual stimuli. Six epileptic subjects were investigated after unilateral temporal lobectomy. Emotionally valenced photographic slides (10 negative, 10 neutral) from the International Affective Picture System were presented to their unilateral visual fields under either subliminal or supraliminal conditions. An interaction between hemispheres and emotional valences was found only under the subliminal conditions; greater EDA responses to negative stimuli compared with neutral ones were observed when stimuli were presented to the intact hemispheres. The findings suggest that nonconscious emotional processing is reflected in EDA in a different manner from conscious emotional processing. Medial temporal structures, including the amygdala, thus appear to play a critical role in the neural substrates for this automatic processing.

Selective spatial memory impairment after right unilateral temporal lobectomy.

Deficits in performance of both spatial and visual tasks are common following tissue loss in the right temporal lobe. Since spatial and visual attributes are frequently confounded in experimental tasks, we have studied patients following unilateral temporal lobectomy, in an attempt to determine which aspect mediates the observed deficits. Spatial and visual memory performance was compared in normal controls (n = 16), left temporal (LTL; n = 19) and right temporal (RTL; n = 19) lobectomy patients, by presentation of eight abstract designs in a spatial array for subsequent recall and recognition of the designs (visual memory) and recall of their spatial position (spatial memory). By varying the retention intervals for each group, all three groups were matched on both recall and recognition of the designs at sub-ceiling levels. In contrast, recall of the position of the designs (spatial memory), tested at equivalent delays to those of the visual memory tests, revealed a deficit in the RTL patients compared to both controls and LTL patients (p < 0.05). Magnetic resonance imaging (MRI) was used to quantify the extent of resection of the hippocampus and parahippocampal regions in the two patient groups and showed a significant correlation between hippocampal and parahippocampal removal and spatial memory in the RTL group only. These data support the notion of a disproportionately large involvement of the right hippocampus and adjacent regions in spatial memory.

Neuropsychological consequences of epilepsy surgery in frontal lobe epilepsy.

The present study investigated the effect of frontal lobe surgery on "cognitive functions", which have previously been shown to be discriminative in the evaluation of non-resected patients with frontal lobe epilepsy (FLE). The cognitive outcome was evaluated with particular consideration of the side (left/right), the site (lateral, orbital, mesial, premotor/SMA), the type of surgery (resections vs. resections plus multiple subpial transections; MST), and seizure outcome. The evaluation is based on 33 patients with left (n = 17) or right (n = 16) frontal surgery. Forty-five patients who underwent successful left (n = 21) or right (n = 24) temporal lobectomy served as controls. The neuropsychological examination covered speed/attention, motor sequencing/coordination, response maintenance/inhibition, short-term memory, and language. With the exception of short-term memory, the chosen tests were discriminative in determining preoperative frontal lobe dysfunctions but they did not differentiate patients with a different lateralization or localization of the frontal focus. At the 3 month follow-up examination, patients with temporal lobectomy had improved frontal functions, whereas patients with frontal lobe surgery showed a mild deterioration. Within the frontally resected group, completely seizure-free patients had significantly improved short-term memory. Further consideration of the side, site and the type of the frontal resection indicated that patients with premotor/SMA surgery and patients with precentral/central MST had additional impairment after surgery. Premotor/SMA resections led to a deterioration in response maintenance/inhibition and if performed left sided also to deteriorated language functions. The latter impairment could be clearly related to transient aphasia directly after surgery. Irrespective of pareses observed immediately after surgery, patients with MSTs of the precentral/central areas displayed additional problems in motor coordination at the follow-up examination. In this group the seizure outcome was also less favourable. In summing up, frontal lobe surgery does not cause any considerable additional impairment in the short-term follow-up. However, caution is recommended when surgery or MST affect functional relevant cortex (here the prefrontal/SMA and precentral/central area). Finally, a release of functions associated with frontal areas not affected by surgery is suggested, when seizures are successfully controlled by surgery.

Differential involvement of the dorsal anterior cingulate and prelimbic-infralimbic areas of the rodent prefrontal cortex in spatial working memory.

The present study examined the effects of quinolinic acid lesions of the dorsal anterior cingulate and prelimbic-infralimbic cortices on spatial working memory and spatial discrimination using go/no-go procedures. All testing occurred in a 12-arm radial maze. In a working memory task, rats were allowed to enter 12 arms for a cereal reward. Three or 4 arms were presented for a 2nd time in a session, which did not result in a reward. In a spatial discrimination task, rats had successive access to 2 different arms. One arm always contained a reward, and the other never contained a reward. Prelimbic-infralimbic lesions impaired spatial working memory but only produced a transient spatial discrimination deficit. Dorsal anterior cingulate lesions did not induce a deficit in either task. These findings suggest that the prelimbic-infralimbic cortices, but not the anterior cingulate cortex, are important in spatial working memory.

Perirhinal cortex contributions to performance in the Morris water maze.

Rats with bilateral, electrolytic lesions of perirhinal cortex (PRC), lateral entorhinal cortex (LEC), or combined lesions (PRLE) were impaired relative to controls (sham) during initial acquisition in the Morris water maze, although all groups were eventually able to learn to locate the platform. A further deficit in the performance of PRC and PRLE, but not LEC groups, was evident, however, when a probe trial was conducted 2 min (but not 24 hours) after training. When the performance of sham- and PRC-lesioned rats was tested with variable memory delays inserted between training and probe trials, lesioned rats displayed an increase in the rate of forgetting for information made available during the training trial. This finding suggests that the PRC normally stores information regarding the cue-platform relationship and transfers this information to related structures during water maze performance.

Light deprivation accelerates recovery from frontal cortical neglect: relation to locomotion and striatal Fos expression.

Rats given unilateral medial agranular (AGm) cortex ablations show neglect for contralateral multimodal stimuli, symptoms that are reversed by 48 hr of light deprivation. To address processes that contribute to this restorative effect, both the rats' locomotion and basal ganglia c-fos expression were studied. AGm-lesioned rats showed less activity in continuous darkness than in normal (12 hr light/12 hr dark) cycles, and the reduced locomotion correlated with the extent of their subsequent behavioral recovery. The AGm ablation reduced the numbers of amphetamine-stimulated Fos-immunoreactive nuclei in the ipsilateral dorsolateral striatum, where the AGm innervation is normally densest. Light deprivation also reduced Fos in this striatal region and attenuated the lesion-induced hemispheric Fos asymmetry. A restored balance of activity between the 2 hemispheres, especially the basal ganglia, appears central to the action of light deprivation.

Anterior temporal lobectomy, hippocampal sclerosis, and memory: recent neuropsychological findings.

Anterior temporal lobectomy (ATL) is an effective and increasingly utilized treatment for nonlesional, intractable mesial temporal lobe epilepsy. However, this surgery results in domain-specific neuropsychological morbidity for a subset of patients. Within the past decade, multidisciplinary studies have revealed that left ATL patients without significant sclerosis in the resected hippocampus are most at risk for a substantial postacute decline in the ability to encode new verbal information. These patients are also at risk for a significant decrement in confrontation naming and other retrieval-based language abilities. The memory deficit is not attributable to this disruption of language. A relationship between hippocampal sclerosis (HS) status and memory performance has not been identified consistently in right ATL patients, but investigation of new visuospatial measures continues. The influence of variables other than HS on neuropsychological outcome is also discussed.

Hippocampal cell loss and gliosis: relationship to preoperative and postoperative memory function.

The authors examined the relationship between neuronal densities, glial cell densities, and the glial cell/neuron ratio in the CA1 and CA4 hippocampal subfields and preoperative and postoperative memory function in 47 patients who had undergone a temporal lobectomy (23 right, RTL; 24 left, LTL) for the relief of medically intractable epilepsy. The LTL group performed more poorly than the RTL group on a list learning and story recall task, preoperatively and postoperatively. Both the RTL and LTL groups performed more poorly on the story recall task postoperatively. In the LTL group, neuronal densities in the CA1 subfield were significantly correlated with the preoperative scores on the immediate (r = 0.53, p < 0.01) and delayed (r = 0.53, p < 0.01) recall of the story. There were no significant correlations in the LTL group between the CA1 and CA4 cell counts and Verbal IQ or scores on a measure of naming ability. None of the cell density measures in the CA1 and CA4 subfields were significantly correlated with the preoperative neuropsychological test scores in the RTL group. Postoperative decline in verbal recall was associated with the excision of a relatively intact left hippocampus, with high neuronal and low glial cell densities in the CA1 subfield. The excision of a relatively intact right hippocampus was also associated with a postoperative deterioration in verbal recall.

Neuropsychological outcome following anterior temporal lobectomy in patients with and without the syndrome of mesial temporal lobe epilepsy.

The nature, pattern, and degree of neuropsychological change following anterior temporal lobectomy (ATL) were examined as a function of the presence or absence of the syndrome of mesial temporal lobe epilepsy (MTLE). Fifty-four patients exhibited the syndrome of MTLE, while 34 patients were without the syndrome (non-MTLE). The test-retest performance of a group of 40 epilepsy patients who did not undergo surgery was used to derive regression-based estimates of test-retest change. Overall, the MTLE group did not show significant cognitive decline following ATL. In contrast, the left non-MTLE group showed significant declines on verbal memory, confrontation naming, and verbal conceptual ability. Further, verbal memory was the most substantial area of decline, and was independent of seizure outcome. Clinical and theoretical implications of these findings are discussed.

Use of the intracarotid amobarbital procedure in the evaluation of memory.

The intracarotid amobarbital procedure (IAP) involves the temporary inactivation of one cerebral hemisphere by the injection of sodium amobarbital, which allows independent testing of the contralateral hemisphere. Initially used for lateralization of language, IAP later found a role in the evaluation of memory function in patients with intractable temporal lobe epilepsy being considered for resective surgery. IAP technique varies widely across centers, but, in general, memory is assessed by presenting the patient with a number of items during the period of hemispheric inactivation and testing recall or recognition of these items after the effect of the drug has worn off. Because the medial temporal lobe is not directly perfused by the internal carotid artery, concerns have been raised about the ability of the IAP to test hippocampal memory function. Consequently, a variety of selective procedures have been devised. Findings on both intracranial EEG recordings and pathologic and neuroimaging studies support the association of IAP memory results with hippocampal function. The IAP memory test was originally designed to predict the risk for development of global amnesia following unilateral temporal lobectomy. More recently, it also has been used as an adjunct in lateralizing the seizure focus and for predicting postoperative selective memory deficits and seizure outcome.

Remote memory in patients with acute brain injuries.

Remote memory was investigated in an unselected sample of 26 patients with either unilateral tumours in the temporal lobes or traumatic brain injuries. Six patients underwent excisions within the left temporal lobe, and nine patients were operated on within the right temporal lobe. In both groups, patients with excisions including and sparing the hippocampal formation were studied. Their performance was compared to that of 11 patients with moderate to severe head trauma and to a normative sample of 214 healthy controls. Remote memory was assessed using a famous events test with items of extremely low salience that had been proven to be of low difficulty for those old enough at the time of the event's actuality. The results show severely disturbed retrograde memory functions in the left temporal tumour group. These patients achieved similar scores to patients with severe traumatic brain injury. Right hemispheric patients showed a pattern of results comparable to that of healthy controls. The strongest effects were in the free recall part of the test. In most of the patients, no graded memory loss was observable. No consistent association to recent memory function could be identified. Since most of the remote memory test items used denoted famous names which were cued by rich semantic information, the type of deficit seen may be best understood in terms of a specific dysfunction of the semantic stores containing information about famous proper names.

Surgical treatment for epilepsy: a retrospective Swedish multicenter study.

The characteristics of patients suffering from drug resistant epilepsy, including the results of the preoperative evaluation and epilepsy surgery were retrospectively analyzed in a Swedish multicenter 10-year cohort of children and adults. Altogether 152 patients (65 children and 87 adults) treated during the period 1980-1990 in three epilepsy centers were included and followed-up 2 years after surgery. Median age at onset of seizures was 4 years for the children and 12 years for the adults. A localization related epilepsy was present in 85% of the children and in 95% of the adults. The mean number of seizure types in the children was 1.7 (range 1-4) and in the adults 1.8 (range 1-4). The median monthly seizure frequency was 52 and 15 for children and adults respectively. Resective surgery was performed in 143 cases (94 temporal, 31 extratemporal, 9 multilobar and 9 major resection procedures) and palliative procedures in 16 cases (13 callosotomies and 3 stereotactic amygdalotomies). Postoperative neurological deficits were detected in 9% of the patients after temporal lobe resections and in 15% of the patients after extratemporal and multilobar resection procedures. Two years after resective surgery 53% of the children and 49% of the adults were seizure free. Another 25% of the patients had a more than 50% reduction of seizure frequency. In the postoperative non seizure free group of patients there was a negative correlation between decrease in weighted seizure severity and decrease in seizure frequency. This finding stresses the need for including other parameters than seizure frequency when evaluating the outcome of epilepsy surgery.

High level object recognition without an anterior inferior temporal lobe.

Seven individuals with unilateral anterior inferior temporal (AIT) lobectomies performed two types of shape recognition tasks with line drawing of 3D objects briefly presented in either the left or the right visual field. In one task, subjects named familiar objects in a name priming paradigm. In the other task, subjects judged whether two objects, presented sequentially with an intervening mask, were the same or different in shape, disregarding differences in orientation of up to 60 degrees in depth. They could not use names or basic level concepts to do the matching as the stimuli were either nonsense objects or, if familiar objects, were of same name-different-shaped exemplars on different trials. The disadvantage of presenting an image to the lobectomized hemisphere was negligible in both tasks. Two non-exclusive possibilities are suggested by this result: (a) Object recognition is completed posterior to AIT, likely at the temporal-occipital boundary, with no deleterious retrograde effects on object recognition from the AIT section, or (b) Callosal transfer of object information prior to AIT is completely efficient. These results, along with results of single unit recording and lesion experiments in the monkey, PET and MRI imaging in humans, and a plausibility argument based on the pattern of callosal connections suggest both are correct. Rather than mediating real-time object recognition, AIT may code representations for visual episodes and scenes.