Foreign Tissue Lesion Research Articles

EPILEPSY SURGERY AND ELECTRONIC DEVICES

Epilepsy is a chronic disorder characterized by recurrent and unprovoked seizures. The lifetime risk of developing epilepsy is 4%. Approximately 90% of the incident cases in adults have partial epilepsy. The initial response to medication is of prognostic importance. Patients with symptomatic neurologic disease, foreign-tissue lesion, or developmental delay are less likely to be rendered seizure free. The goal of treatment is to render the individual seizure free. Many patients with partial epilepsy will not attain a seizure remission with antiepileptic drug therapy. Epilepsy surgery is an effective and safe alternative form of therapy for selected patients with intractable partial epilepsy. Electronic stimulation is being considered for patients with partial seizures who are not candidates for a focal cortical resection.

When drugs and surgery don’t work

Epilepsy is a chronic disorder characterized by recurrent and unprovoked seizures (Dreifuss, 1987; Hauser & Hesdorffer, 1990). It is one of the most common neurologic disorders in the adult. The lifetime risk of developing epilepsy is 3.2% (Mattson, 1992). Approximately 90% of the incident cases in adults have symptomatic partial or localization-related epilepsy (Camfield & Camfield, 1996; Hauser & Hesdorffer, 1990; Hauser, 1992). The medial temporal lobe is the most epileptogenic region of the brain (Luby et al., 1995; Jeong et al., 1999; Wiebe et al., 2001). Pathologic lesions underlying the epileptogenic zone include mesial temporal sclerosis (MTS), tumor, vascular anomaly, malformations of cortical development (MCDs), and head trauma (Cascino et al., 1993; Radhakrishnan et al., 1998). The initial response to medication is of prognostic importance (Hauser, 1992). Patients with a remote symptomatic neurologic disease, foreign-tissue lesion, developmental delay, or abnormal neurologic examination are less likely to be rendered seizure-free. The goals of treatment are to render the individual seizure-free without producing antiepileptic drug (AED) toxicity, allowing the individual to become a participating and productive member of society (Engel & Ojemann, 1993). Despite the introduction of "newer" AEDs, nearly one-half of patients with partial epilepsy will not attain a seizure remission with pharmacotherapy (Kwan & Brodie, 2003). This discussion focuses on management of the adult patient with intractable partial seizure disorders that are medically refractory and may not be surgically remediable. It is estimated that 400,000 of the 2 million individuals with partial epilepsy in the United States have a medically refractory partial seizure disorder (Hauser & Hesdorffer, 1990; Hauser, 1992). An estimated 1,500 patients in the United States undergo epilepsy surgery each year. A UK study indicated that 30,000 patients develop epilepsy each year and approximately 6,000 have medically refractory seizures (Lhatoo et al., 2003). However, there are only about 400 epilepsy surgeries performed annually in the UK. Therefore, the number of patients with intractable partial epilepsy that is both medically refractory and possibly not a surgically remediable epileptic syndrome is significant.

Preoperative evaluation for temporal lobe surgery.

Temporal lobe epilepsy (TLE), the most common form of partial epilepsy in adults is often refractory to medical treatment and in these patients epilepsy surgery is considered. Successful surgery is dependent on accurate localisation and lateralisation of the epileptogenic zone. The preoperative evaluation involves a series of assessments and investigations including detailed clinical history, interictal EEG, video-EEG monitoring, MRI, PET, SPECT, and neuropsychology and neuropsychiatric assessment. The role of each of these investigations and assessments in the preoperative evaluation is discussed. Advanced MR techniques including magnetic resonance spectroscopy, MR diffusion and MR perfusion have recently been assessed and are likely to enhance the pre-surgical evaluation of patients with TLE.The surgical outcome and preoperative investigations performed of 80 consecutive patients who underwent temporal lobe surgery between 1993 and 2002 at Royal Melbourne Hospital were reviewed. All patients had MRI, video-EEG monitoring and neuropsychology assessment and 56% a PET scan. During a mean follow-up of 5.9 years 75% had Class 1 outcome, 22% non-Class 1 outcome and 3% were lost to follow-up. The results of preoperative investigations were correlated with outcome. For interictal EEG, seizure semiology, ictal EEG, PET and neuropsychology assessment the surgical outcome of patients in whom results were concordant to side of surgery was compared with those discordant or non-lateralising. There was no significant difference. In 78 of 80 patients MRI revealed mesial temporal sclerosis or a foreign tissue lesion. The outcome was no different between these two groups. Results suggest that in patients with unilateral temporal lobe lesion on MRI and where ictal EEG is either concordant or non-lateralising, other investigations including PET, provide little additional prognostic information.

Clinical patterns of patients with temporal lobe epilepsy and pure amygdalar atrophy.

MRI volumetric measurements (MRIvol) have been proven reliable in determining mesial temporal atrophy in patients with TLE. We attempted to correlate the clinical features with different patterns of hippocampal formation (HF) and amygdala (AM) atrophy in patients with TLE without foreign tissue lesion. We studied 65 patients with refractory TLE. They were divided into five groups according to MRIvol results: pure AM atrophy (n = 11, 10 unilateral and one bilateral), unilateral HF atrophy (n = 16), bilateral HF atrophy (n = 12), unilateral AM + HF atrophy (n = 13), and patients with normal volumes of AM and HF (n = 13). MRIvol of AM and HF were performed by using a protocol previously described by Watson et al. (Neurology 1992;42:1743-50). Patients with AM atrophy had later onset of seizures compared with those with unilateral HF atrophy (p < 0.01). History of febrile convulsions (p < 0.0001) and frequent secondarily generalized tonic-clonic seizures (GTCSs) were more often found in patients with HF atrophy compared with those with pure AM atrophy and those with normal volumes (p = 0.04). Prolonged postictal confusion was more often found with AM atrophy (p = 0.05). Memory impairment was more severe in patients with HF atrophy than in those with AM atrophy only or in those with normal volumes (p = 0.03). There were no significant differences among the five groups in the following parameters: age, duration of epilepsy, seizure frequency, and presence and type of aura. Prolonged postictal confusion appeared to be related to AM atrophy, in keeping with previous clinical observations. These patients also had a lower incidence of early febrile convulsions, older age at epilepsy onset, lower frequency of secondary GTCS, and lesser memory dysfunction compared with patients with hippocampal atrophy.

Quantitative MRI of Mesial Temporal Structures in Temporal Lobe Epilepsy

Summary: Hippocampal sclerosis (HS) is the most common pathology associated with intractable temporal lobe epilepsy (TLE). MRI features of HS include hippocampal atrophy and an increased T2 signal. Hippocampal volume loss can be quantified using MR‐based hippocampal volume measurement, and the hippocampal T2 relaxation time can be measured on a hippocampal T2 map. Visual assessment of high quality T2‐and thin sliced IR TI‐weighted images along the axes of the hippocampus allows reliable detection of unilateral diffuse HS, the most common variant of HS. A combination of quantitative hippocampal MRI techniques may be required to detect some variants of HS, such as bilateral HS, and to better define the range of normality. Examples of unusual findings are presented and clinical correlations are discussed. The combination of AT2 mapping and FLAIR is a sensitive method with which to detect small lesions which are not seen on standard MR images in the amygdalae of patients with intractable TLE. These MRI techniques will detect an abnormality in mesial temporal structures in ∼80% of patients with intractable TLE not associated with a foreign tissue lesion.

Non-invasive investigations successfully select patients for temporal lobe surgery

OBJECTIVESThere is controversy regarding the need for invasive monitoring in the preoperative assessment of patients with temporal lobe epilepsy. The use of a series of non-invasive investigations in identifying the...

Interictal 99Tc(m) HMPAO SPECT and 1H MRS in children with temporal lobe epilepsy.

To understand the pathological basis of focal hypoperfusion seen on interictal 99Tc(m) hexamethylpropyleneamine oxime (HMPAO) single-photon-emission computed tomography (SPECT) in intractable temporal lobe epilepsy, and to determine why the technique may be misleading in the localization and lateralization of the seizure focus in some cases. Interictal 99Tc(m) HMPAO SPECT and proton magnetic resonance spectroscopy (1H MRS) of the mesial temporal regions were performed in 14 children with intractable temporal lobe epilepsy not caused by a foreign tissue lesion. Hypoperfusion of one temporal lobe ipsilateral to the seizure focus was demonstrated in 10 (71%) of the children; 1H MRS correctly lateralised in eight of these 10. No asymmetry of perfusion of the anterior temporal regions was seen in the remaining four children; on 1H MRS, three of these were bilaterally abnormal but nonlateralising. Repeated SPECT and 1H MRS in three children demonstrated changes over time, the findings from the two techniques being consistent with each other on both the initial and the repeated scans. Abnormalities demonstrated by 1H MRS correlate well with those seen on interictal SPECT and can help to understand the pathologic basis of these SPECT abnormalities. Furthermore, the presence of bilateral damage can result in an absence of perfusion asymmetry on interictal SPECT.

Temporal lobe epilepsy subtypes: differential patterns of cerebral perfusion on ictal SPECT.

We studied cerebral perfusion patterns in the various subtypes of TLE, as determined by pathology and good outcome after temporal lobectomy (as confirmation of temporal origin). We studied clinical features and ictal technetium 99m hexamethyl-propyleneamineoxime (99mTc-HM-PAO) single-photon emission-computed tomography (SPECT) in four subgroups of patients with intractable temporal lobe epilepsy (TLE) treated with surgery: hippocampal sclerosis (group 1, n = 10), foreign-tissue lesion in mesial temporal lobe (group 2, n = 8), foreign-tissue lesion in lateral temporal lobe (group 3, n = 7), and normal temporal lobe tissue with good surgical outcome (group 4, n = 5). No major clinical differences in auras, complex partial seizures or postictal states were identified among the groups. Ictal SPECT showed distinct patterns of cerebral perfusion in these subtypes of TLE. In groups 1 and 2, hyperperfusion was seen in the ipsilateral mesial and lateral temporal regions. In group 3, hyperperfusion was seen bilaterally in the temporal lobes with predominant changes in the region of the lesion. Hyperperfusion was restricted to the ipsilateral anteromesial temporal region in group 4. Ipsilateral temporal hyperperfusion in mesial onset seizures can be explained by known anatomic projections between mesial structures and ipsilateral temporal neocortex. Bilateral temporal hyperperfusion in lateral onset seizures can be explained by the presence of anterior commissural connections between lateral temporal neocortex and the contralateral amygdala. We conclude that the perfusion patterns seen on ictal SPECT are helpful for subclassification of temporal lobe seizures, whereas clinical features are relatively unhelpful. These perfusion patterns provide an insight into preferential pathways of seizure propagation in the subtypes of TLE.

Quantitative hippocampal MRI and intractable temporal lobe epilepsy.

To evaluate and compare T2 relaxometry and volumetrics of hippocampus in the presurgical evaluation of patients with intractable temporal lobe epilepsy (TLE), and to correlate these quantitative MRI measures with the pathology of the resected hippocampus. Forty patients with intractable TLE who underwent presurgical evaluation and subsequent temporal lobe surgery. Hippocampal T2 (HCT2), volumes of hippocampi and hippocampal volume ratio (HCVR) (volume of hippocampus with higher HCT2 divided by volume of hippocampus with lower HCT2), and qualitative pathology. Thirty-two patients had hippocampal sclerosis, three patients had end-folium sclerosis, one patient had amygdala sclerosis, and four patients had a foreign tissue lesion in the temporal lobe. HCT2 (R/L) correlated inversely with the ratio of hippocampal volumes (R/L) (r = -0.91; p < 0.0001). A high T2 signal in an atrophic hippocampus was characteristic of hippocampal sclerosis. All patients with hippocampal sclerosis had an HCVR below control values, and only one of these had an HCT2 in the normal range. HCVR produced one false-positive result. The patients with end-folium sclerosis had normal HCT2 and HCVR. The patient with amygdala sclerosis had a normal hippocampus on qualitative and quantitative assessment. Of the four patients with a lesion, one had a mildly increased HCT2 and one had mild volume asymmetry. Hippocampal volume asymmetry could be reliably detected on visual inspection of the MRI with an HCVR of 0.85 or less, and an increase of HCT2 with a T2 of 115 msec or higher. Quantitative MRI combining HCT2 and HCVR is a reliable method for diagnosing hippocampal sclerosis noninvasively. End-folium sclerosis and amygdala sclerosis should be considered in patients with intractable TLE and negative findings on MRI studies, including quantitative measures of the hippocampus.

Fractal Description of Cerebral Cortical Patterns in Frontal Lobe Epilepsy

The convoluted pattern of normal cerebral cortex resists description by Euclidean geometry. However, subtle abnormalities often unrecognised in vivo may underlie a wide range of neurological disorders. Abnormalities of cortical morphology frequently characterise these lesions, and we applied fractal geometry in an attempt to quantify these abnormalities. We have demonstrated typical fractal scaling properties for the cortical-white matter interface on axial and coronal MR images, with a fractal dimension (Df) of 1.45 +0.06 (mean +1 standard deviation) in normal subjects. We have also applied this to 16 patients with frontal lobe epilepsy, a condition associated with subtle disruptions of the cortical ribbon, all of whom had no obvious abnormality on visual inspection of the images. Nine of these 16 had a Df < 1.27 (mean -3 standard deviations). A control group of 10 patients with temporal lobe epilepsy with a focal foreign tissue lesion (vascular or tumoural) all had Df in the normal range. Analysis of shape using this method identifies subtle abnormalities of the cortical ribbon, and has potential application to images of the human brain in a wide range of clinical and pathophysiological settings.

Extratemporal cortical resections and lesionectomies for partial epilepsy: complications of surgical treatment.

Fifty patients with medically refractory extratemporal seizures underwent epilepsy surgery at our institution between 1988 and 1992. Twenty-nine patients (group I) had an extratemporal (mainly frontal lobe) corticectomy, and 21 patients (group II) had an epileptogenic lesion extirpated without resection of the epileptic brain tissue. Comprehensive neurologic evaluation was performed preoperatively, soon after operation, and approximately 3 months postoperatively to assess operative outcome. Magnetic resonance imaging (MRI) in group I patients usually showed no abnormality or a large destructive lesion. Neuroimaging showed a foreign tissue lesion in most group II patients. Thirteen of the 29 patients who underwent corticectomy had at least one adverse event (AE) potentially related to operation at the time of initial assessment. Four of the 13 patients required a surgical procedure to treat the operative complication, but only 1 of the 13 patients had a persistent neurologic deficit at follow-up examination. Three of the 21 patients who received lesionectomy had acute and persistent neurologic morbidity. Patients undergoing cortical resection remained intubated longer postoperatively (p < 0.005), and required longer hospitalization after operation (p < 0.001) and in the intensive care unit (p < 0.001) as compared with the lesionectomy group. Results of this study may prove useful in counseling patients regarding neurologic outcome after extratemporal surgery.

Parietal lobe lesional epilepsy: electroclinical correlation and operative outcome.

We retrospectively studied ictal behavior, extracranial EEG, and operative outcome in 10 consecutive patients with intractable partial epilepsy of presumed parietal lobe origin who received a lesionectomy, i.e., resection of the neuroimaging-identified abnormality, at the Mayo Clinic. Nine patients had a pathologically verified foreign-tissue lesion, e.g., tumor or vascular malformation, and 1 patient had gliosis. All patients with foreign-tissue lesions were rendered seizure-free. The patient with gliosis experienced a reduction in seizure tendency. There were no operative complications. The most common seizure type was a simple partial seizure with visual, motor, or sensory symptoms (n = 8). Complex partial seizures (n = 5) and secondarily generalized tonic-clonic seizures (GTC, n = 2) were also observed. The ictal behavior was often nonspecific although useful in identifying lateralization of the epileptogenic zone. Extracranial interictal and ictal EEG changes were unreliable markers of the parietal lobe origin of seizure activity. Lesionectomy without chronic intracranial monitoring or functional mapping may be an effective and safe alternative surgical procedure in patients with partial epilepsy related to parietal lobe lesions.

Operative strategy in patients with MRI-identified dual pathology and temporal lobe epilepsy

We performed a prospective study using preoperative magnetic resonance imaging to identify hippocampal formation atrophy in 15 consecutive patients with intractable partial epilepsy who had undergone a stereotactic resection of an extrahippocampal temporal lobe foreign-tissue lesion. A stereotactic lesionectomy was performed in all patients, i.e., only the imaging-defined lesion itself was resected. Hippocampal formation atrophy was identified in three of the 15 patients. Neuroimaging-detected hippocampal formation atrophy has been shown to be a reliable marker of moderate to severe mesial temporal sclerosis. All patients with hippocampal formation atrophy had an unfavorable operative outcome. Pathological examination of the hippocampus in one patient with neuroimaging-identified hippocampal formation atrophy who subsequently received an anterior temporal lobectomy revealed mesial temporal sclerosis. Nine of the 12 patients without hippocampal formation atrophy experienced a significant reduction in seizure tendency after lesionectomy. The surgically excised hippocampus in one patient without hippocampal formation atrophy who later underwent a temporal lobectomy showed no significant neuronal loss. Results of this study have modified the surgical approach taken at this institution in patients with temporal lesional epilepsy. Patients with magnetic resonance imaging-defined dual pathology now undergo a temporal lobectomy which includes resection of the hippocampus and the foreign-tissue lesion.

Predictive value of magnetic resonance imaging in temporal lobe epilepsy surgery.

The predictive value of magnetic resonance imaging (MRI) was assessed by a prospective study of 34 patients selected for surgical treatment of temporal lobe epilepsy. The MRIs were interpreted using standardized visual diagnostic criteria and the imaging findings were correlated with the surgical outcome. Lateralized MRI abnormalities were found in 25 (74%) of 34 patients. Significant associations were found between either the presence of a restricted foreign-tissue lesion or hippocampal atrophy and an excellent surgical outcome. An abnormal MRI had an 82% predictive value and a normal MRI had a 56% predictive value for surgical success. A history of febrile convulsions and the presence of hippocampal atrophy best predicted outcome (predictive value, 86%). These results suggest that specific MRI findings in candidates for temporal lobe epilepsy surgery are predictive of surgical outcome. The information provided by MRI may be of value for counseling patients prior to surgical intervention.

A comparative study of lesionectomy versus corticectomy in patients with temporal lobe lesional epilepsy

We performed a retrospective study comparing surgical outcome of anterior temporal lobectomy (n = 20) and stereotactic lesionectomy (n = 14) in 34 consecutive patients with intractable partial epilepsy evaluated at this institution between June 1986 and June 1992. All patients had medically refractory partial seizures and a neuroimaging-identified temporal lobe foreign-tissue lesion. Patients underwent a pre- and postoperative comprehensive evaluation. In all patients, postoperative neuroimaging studies indicated complete lesion resection. Seventy-one percent of lesionectomy patients and 90% of lobectomy patients, respectively, experienced a worthwhile reduction in seizure tendency. Forty-three percent of lesionectomy patients and 85% of lobectomy patients, respectively, were seizure-free postoperatively. Mean duration of follow-up was 51 months (range, 21–83 months). Morbidity occurred in three patients who underwent corticectomy: complete homonymous hemianopsia (1) and dysphasia (2). No significant morbidity was associated with lesionectomy. Results of this study have altered the surgical strategy at this institution for patients with temporal lobe lesional epilepsy and have proved useful in counseling patients regarding neurologic outcome.

Postictal Psychosis After Partial Complex Seizures: A Multiple Case Study

Bouts of unusually frequent partial complex seizures originating in the temporal lobe, that sometimes became secondarily generalized, induced psychotic episodes in 9 patients. In 7, the increase in seizures occurred at a time when antiepileptic drugs (AEDs) were being reduced during intensive EEG monitoring with a view to surgical treatment of intractable epilepsy. According to DSM-III-R criteria, the postictal psychosis resembled an organic delusional syndrome which was paranoid in 7 and schizophreniform in 1 and an organic mood syndrome in 1. A high incidence of ictal fear, of bilateral independent epileptogenic discharge, and of small foreign tissue lesion were unexpected findings and appeared to represent risk factors, especially in patients otherwise handicapped by an epileptic personality disorder. Recognition of postictal psychosis in this setting and in others is important both prognostically and therapeutically. Postictal psychosis does not constitute a contraindication to surgical treatment of epilepsy.