Occipital Lobe Epilepsy: Clinical Characteristics ... - Semantic Scholar

Epilepsia, 46(5):688–695, 2005 Blackwell Publishing, Inc. C 2005 International League Against Epilepsy

Occipital Lobe Epilepsy: Clinical Characteristics, Surgical Outcome, and Role of Diagnostic Modalities ∗ Sang Kun Lee, ∗ Seo Young Lee, ∗ Dong-Wuk Kim, †Dong Soo Lee, and ‡Chun-Kee Chung ∗ Departments of Neurology, †Nuclear Medicine, and ‡Neurosurgery, Seoul National University College of Medicine, Seoul, Korea

Summary: Purpose: To assess the role of various diagnostic modalities, to identify surgical prognostic factors and concordances with presurgical evaluations, and to characterize the clinical features of occipital lobe epilepsy (OLE), we studied 26 patients who were diagnosed as having OLE and underwent epilepsy surgery. Methods: Diagnoses were established by standard presurgical evaluations, which included magnetic resonance imaging (MRI), fluorodeoxyglucose–positron emission tomography (FDG-PET), ictal single-photon emission computed tomography (SPECT), scalp video-EEG monitoring, and intracranial EEG monitoring. After epilepsy surgery, patients were followed up for >2 years. Results: Sixteen (61.5%) of the 26 became seizure free after surgery, and another eight patients had a favorable outcome. Sixteen of the 26 patients experienced a type of visual aura (i.e., visual hallucination, visual illusion, blindness, or a field defect). Nine patients had both automotor seizures and secondary generalized tonic–clonic seizures at different times. Interictal EEG showed correctly localizing spikes in 10 of the 16 patients who became seizure free, and in three of the 10 non–seizure-free patients. MRI correctly localized the lesion in seven of these 16

seizure-free patients, and in three of the 10 non–seizure-free patients. FDG-PET correctly localized the lesion in eight of the 16 seizure-free patients, and in three of nine non–seizure-free patients. Ictal SPECT was performed in 19 patients and correctly localized the lesion in only three of 12 seizure-free patients, and in four of seven non–seizure-free patients. Ictal EEG correctly localized the lesion in 13 of the 16 seizure-free patients, and in five of the 10 non–seizure-free patients. No significant relation was found between the diagnostic accuracy of any modality and surgical outcome. The localizations of epileptogenic zones by these different diagnostic methods were complementary. The concordance of three or more modalities was significantly observed in seizure-free patients (p = 0.042). However, no definite relation was observed between the presence of lateralizing clinical seizure manifestation and surgical outcome (p = 0.108). Conclusions: Some specific auras indicated an occipital epilepsy onset. Various diagnostic methods can be useful to diagnose OLE, and a greater concordance between presurgical evaluation modalities indicates a better surgical outcome. Key Words: Occipital lobe epilepsy—Characteristics— Surgical outcome—Prognostic factors—Diagnostic modalities.

Although it has been regarded as a relatively uncommon epilepsy syndrome (1–5), occipital lobe epilepsy (OLE) is now increasingly diagnosed on the basis of its characteristic semiology and with the aid of various diagnostic tools (6,7). Surgery is also increasingly considered in those with medically refractory OLE (8–13), and total lesion excision (14) and the focal nature of an occipital lesion (8,9) have been shown to predict an improved surgical outcome. In patients that receive surgical resection, functional neuroimaging such as fluorodeoxyglucose–positron emission tomography (FDG-PET) and ictal single-photon emission computed tomography (SPECT) may aid in confirming an occipital epileptogenic zone (6,15,16). These techniques may be valuable especially in those without a structural lesion on MRI, and the identification of the clin-

ical implications of neuroimaging modalities is an important aspect of deciding on surgery. However, reports about the roles of these functional neuroimaging techniques in the diagnosis of OLE are limited. Furthermore, no clear reports are available regarding the relations between the results of various diagnostic tools and surgical outcome. The main aim of this study was to assess the roles of various diagnostic modalities and to understand the relations between the results obtained by using these diagnostic modalities and surgical outcome. In addition, we analyzed the concordance between various presurgical evaluations in OLE and assessed the relations between these concordances and surgical outcome. We also attempted to characterize the clinical features of OLE. PATIENTS AND METHODS

Accepted January 12, 2005. Address correspondence and reprint requests to Dr. S.K. Lee at Department of Neurology, Seoul National University Hospital, 28, Yonggonn dong, Jongro Gu, Seoul, 110-744, Korea. E-mail: sangunlee@ dreamwiz.com

Patients Twenty-six consecutive patients diagnosed as having OLE at Seoul National University Hospital from 688

OCCIPITAL LOBE EPILEPSY September 1994 to August 2001 were included in the study. The diagnostic criteria used for OLE were the presence of either a discrete lesion in the occipital lobe on MRI with compatible intracranial ictal EEG, or the presence of an exclusive ictal-onset zone in the occipital lobe confirmed by intracranial EEG. The 16 men and 10 women were aged between 14 and 44 years (mean, 25.9 ± 7.6 years). Age at seizure onset ranged from 1 to 25 years (mean, 11.4 years), and the duration of illness, from 5 to 26 years (mean, 14.1 years). All patients had intractable epilepsy, despite taking appropriate anticonvulsant medication (AEDs). Surgery was performed in all patients. The postoperative follow-up duration was >2 years in all patients. Surgical outcome was analyzed by using the Engel classification (17) and “seizure-free” or “non–seizure-free” categorization. We analyzed the prognostic values of each diagnostic modality by comparing the results of the postoperative seizure-free and non–seizure-free groups. We also analyzed the diagnostic sensitivity of each modality in patients that achieved a seizure-free status. In addition, we tried to identify the characteristic semiology of OLE and the prognostic value of a lateralizing semiology. Presurgical evaluation MR imaging All patients underwent brain MRI. Standard MRI was performed on either a 1.0-T or a 1.5-T unit (Signa Advantage; General Electric Medical Systems, Milwaukee, WI, U.S.A.) with conventional spin-echo T1 -weighted sagittal and T2 -weighted axial and coronal sequences in all patients. Section thickness and conventional image gaps were 5 mm and 1 mm, respectively. Additionally, T1 -weighted 3D magnetization-prepared rapid acquisition with gradient-echo sequences and 1.5-mm-thick sections of the whole brain, and T2 -weighted and fluid attenuated inversion recovery (FLAIR) images with 3mm-thick sections were obtained in the oblique coronal plane of the temporal lobe. The angle of the oblique coronal imaging was perpendicular to the long axis of the hippocampus. The spatial resolution was approximately 1.0 × 1.0-mm (matrix, 256 × 256-mm; field of view, 25 cm). These sequences, except FLAIR images, were performed in all subjects. The FLAIR sequence was not done in five subjects. FDG-PET PET was performed in 25 patients during the interictal period (no seizures for >24 hours). Axial raw data were obtained on a PET scanner (ECAT EXACT 47; SiemensCTI, Knoxville, TN, U.S.A.) 60 min after the intravenous injection of [18 F]fluorodeoxyglucose (FDG; 370 MBq). The acquisition time was ∼20 min. The axial images were reconstructed by using a Shepp-Logan filter (cutoff frequency, 5 cycles per pixel) and realigned in the

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coronal and sagittal planes. Spatial resolution was 6.1 × 6.1 × 4.3 mm. FDG-PET images were assessed by visual and statistical parametric mapping (SPM) analysis. For SPM analysis, spatial preprocessing and statistical analysis were performed by using SPM 99 (Statistical Parametric Mapping 99; Institute of Neurology, University College of London, London, U.K.). All reconstructed FDG-PET images were spatially normalized onto a Montreal Neurological Institute (McGill University, Montreal, Quebec, Canada) standard templates by affine transformation (12 parameters for rigid transformations, zooms, and shears) and by nonlinear transformation. Normalized images were smoothed by convolution with an isotropic gaussian kernel having a 16-mm full width at half-maximum to increase the signal-to-noise ratio. The effects of global metabolism were removed by normalizing the count of each voxel with respect to the total brain count by using proportional scaling. Each patient image was compared with the images of 22 age-matched healthy volunteers at every voxel, by using an unpaired t test at two contrast levels to detect any regional decrease in metabolism. The threshold was set at an uncorrected p value of 0.001. Results were displayed on three orthogonal planes of an MRI template. Areas with highest significance were considered to be epileptogenic areas. Interictal and ictal SPECT Ictal SPECT was performed on 19 patients during video-EEG monitoring. 99m Tc was mixed with hexamethylpropylene amine oxime (HMPAO; 925 MBq) and injected as soon as a seizure started. Brain SPECT images were acquired within 2 h after the injection by using a triple-head rotating Gamma camera (Prism 3000; Picker, Cleveland, OH, U.S.A.) with a high-resolution fan beam collimator. Brain-perfusion SPECT was acquired by using the step-and-shoot method at 3-degree intervals by using a 128 × 128 matrix. The whole acquisition lasted 15 min. Interictal SPECT was also performed to identify perfusion changes. Subtraction method SPM 99 (Statistical Parametric Mapping 99; Institute of Neurology, University College of London, U.K.) implemented in Matlab 5.3 (Mathworks Inc., Natick, MA, U.S.A.) was used to realign ictal and interictal SPECT images and to normalize these SPECT images spatially into standard templates. First, ictal and interictal SPECT images were realigned with each other, and then individual ictal and interictal SPECT images were spatially normalized into the SPECT template provided by the SPM software. Parameters for the spatial normalization were obtained from interictal SPECT images and applied to both ictal and interictal SPECT images. Spatially normalized images were smoothed by convolution with an isotropic gaussian kernel. Pixel counts of SPECT images were normalized versus mean pixel counts of gray matter in each Epilepsia, Vol. 46, No. 5, 2005

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SPECT image, which was measured by using a probabilistic map of gray matter with the following equation Ii, j,k × G i, j,k i, j,k

G i, j,k

i, j,k

where I i,j,k and Gi,j,k are the pixel counts of SPECT images and probabilistic maps of gray matter at the (i, j, k)th pixel, respectively. Probabilistic map provided by SPM also was used. Perfusion-change maps were calculated by using the following equation Iic − Iin × 100(%) Iin where I ic and I in are normalized ictal and interictal SPECT images, respectively. A perfusion change >20% was regarded as significant, and perfusion-change maps of significant pixels was superimposed on the T1 MRI template. Video-EEG monitoring In all patients, interictal/ictal scalp EEGs were recorded by using a video-EEG monitoring system with electrodes placed according to the International 10–20 system, and with additional anterior temporal electrodes. We performed intracranial EEG monitoring in all patients with the combination of grids and strips. Grid and strip placements were determined by using the results of ictal scalp EEG, PET, ictal SPECT, and clinical semiology. In all patients, at least three habitual seizures were recorded during scalp and intracranial EEG monitoring. When necessary, pre- and intraoperative functional mapping and intraoperative electrocorticography (ECoG) also were performed. Decision to perform surgery The criteria for surgical resection were as follows: (a) the presence of either a discrete lesion in the occipital lobe on MRI with compatible ictal EEG, and (b) an exclusive ictal-onset zone confirmed by intracranial EEG. However, in two patients, resection was incomplete because of the involvement of the eloquent cortex. We had to perform modified resection in these two patients with preexisting irregular field defect because of concerns about severe field constriction after the surgery. Ictal-onset area was defined by electrodes that showed an initial ictal rhythm before clinical seizure onset, which was reasonably discernible from background activities. Evaluations of the diagnostic sensitivities of noninvasive studies To exclude the possibility of the false localization of epileptogenic foci, the localizing and lateralizing values of individual modalities were analyzed only in the seizurefree patients. Interictal/ictal scalp EEGs were reviewed and classified by two epileptologists after a consensus had been reached. Epilepsia, Vol. 46, No. 5, 2005

Ictal and interictal EEGs were classified as follows: (a) a localizing pattern of ictal-onset rhythm/interictal spike was defined as a localized ictal rhythm/interictal spike confined to the electrodes of an epileptogenic lobe or two adjacent electrodes; (b) a lateralizing pattern was defined as an ictal-onset rhythm/interictal spike in the electrodes of multilobes, including the epileptogenic lobe, but lateralized to the epileptogenic hemisphere; (c) bilateral pattern was defined as ictal-onset rhythm/interictal spike in bilateral hemispheric; (d) a false-localizing was defined as an ictal-onset rhythm/interictal spike in the electrodes of other lobes than the epileptogenic lobe in the ipsilateral hemisphere; and (e) a false-lateralizing pattern was defined as an ictal rhythm/interictal spike in the hemisphere contralateral to the hemisphere containing the epileptogenic lobe. FDG-PET and ictal–interictal subtraction SPECT were reviewed by one experienced physician who was unaware of the clinical histories or the results of other presurgical evaluations. The SPECT images also were evaluated by side-by-side visual analysis. The results of FDG-PET and SPECT were classified as localizing, lateralizing, nonlateralizing, or false-localizing/false-lateralizing (Table 1). Statistical significance was assessed by using the χ 2 test or Fisher’s exact test. Pathological diagnosis Tissue sections from cortical resections were immersion-fixed in 10% buffered formalin, embedded in paraffin, and stained with hematoxylin and eosin, Bielschowsky, and cresyl violet stains. A diagnosis of pathological cortical dysplasia (CD) was made according to the grading system of Mishel et al. (18). Specimens were evaluated for the presence of nine specific microscopic and other abnormal features. The nine microscopic features were (a) cortical laminar disorganization, (b) single heterotopic white matter neurons, (c) neurons in the cortical molecular layer, (d) persistent remnants of subpial granular cell layer, (e) marginal glioneuronal heterotopia, (f) polymicrogyria, (g) white matter neuronal heterotopia, (h) neuronal cytomegaly with associated cytoskeletal abnormalities, and (i) balloon cell change. Criteria (a) to (e) were classified as mild CD and (f) and (g) as moderate CD. Pathological findings of (h) or (i) were regarded as severe CD.

TABLE 1. Classification of interictal fluorodeoxyglucose–positron emission tomography and ictal single-photon emission computed tomography findings Localizing Lateralizing Nonlateralizing False-localizing False-lateralizing

Localize the epileptogenic lobe Multilobar including epileptogenic lobe within the epileptogenic hemisphere Normal or multilobar in both hemispheres Other lobes in the epileptogenic hemisphere Contralateral hemisphere

OCCIPITAL LOBE EPILEPSY TABLE 2. Auras in occipital lobe epilepsy Aura

TABLE 4. Changes in visual field defect after surgery

Number of patients (%)

Elementary visual hallucination Visual illusion Blindness and field defect Dizziness Epigastric rising sense

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9 (34.6%) 7 (26.9%) 4 (15.4%) 4 (15.4%) 2 (7.7%)

Aura was present in 22 of 26 patients. Multiple auras were present in a single patient.

Visual field Normal Quadrantanopsia Hemianopsia Other types of visual defect Before to after operation Normal to normal field Normal to defect Increased defect No change of defect

Before operation

After operation

18 2 4 2

1 14 8 3 Number of patients 1 15 6 4

RESULTS Auras and initial seizure manifestation Twenty-two of the 26 patients experienced or had experienced at least one type of aura before seizure (Table 2). Elementary visual hallucination as an aura was reported most frequently (nine patients, 34.6%). The second most common aura was visual illusion (in seven, 26.9%), followed by blindness or field defect and dizziness. Sixteen patients had a visual type of aura, such as hallucination, illusion, blindness, or field defect. Rapid eye blinking as an initial seizure manifestation with or without visual aura was observed in four patients. Objective seizure manifestation Objective seizure manifestation also was classified according to semiologic seizure classification (19,20). Eight patients showed predominantly secondarily generalized tonic–clonic seizures (2GTCSs), and five patients had automotor seizures. Another four patients showed automotor seizures followed by 2GTCSs. Nine patients had both automotor seizures and 2GTCSs manifested at different times. Surgery All patients underwent surgical treatment. We also placed intracranial electrodes in all patients. Occipital lobectomy was performed in eight patients, and partial neocortical resection with or without lesionectomy in 18. Surgical outcome All patients were followed-up for ≥2 years after surgery (Table 3). Sixteen (61.5%) became seizure free, and another eight patients had a favorable outcome (seizure reduction >90%).

sia, or irregular shaped visual field defects (Table 4). Postoperatively 25 patients had visual field defects, and 14 of these had quadrantanopsia. Visual field defects increased or newly developed in 21 patients after surgery. One patient did not show any visual field defect before or after occipital neocortical resection, and another patient with a previous small irregular field defect showed no increase of defect after occipital resection. Pathology The 20 CDs ranged from mild to severe degree (Table 5). CD was identified as the epileptogenic lesion in all 16 patients with normal MRIs. Diagnostic sensitivity and prognostic value of the various presurgical evaluations We analyzed the prognostic values of the various diagnostic modalities with ≥2-year follow-up (Table 6). Interictal EEG showed correctly localizing spikes in 10 of 16 patients that achieved a seizure-free status, and in three of 10 that did not. MRI correctly localized the lesion in seven of 16 seizure-free patients and in three of 10 patients not seizure free, which was not significant. FDG-PET correctly localized the lesion in eight of 16 seizure-free patients, and in three of nine non–seizure-free patients. Ictal SPECT was performed in 19 patients and correctly localized the lesion in only three of 12 seizure-free patients, and in four of seven non–seizure-free patients. Ictal EEG correctly localized the lesion in 13 of 16 seizure-free patients, and in five of 10 non–seizure-free patients. No significant relation was found between the diagnostic accuracy of any modality and surgical outcome (Table 6). More detailed

Visual field defect before and after surgery Eighteen patients had a normal visual field before surgery, whereas others had quadrantanopsia, hemianop-

TABLE 5. Pathology of surgical specimen Pathology

TABLE 3. Surgical outcome Engel classification Seizure free Rare seizure 90% seizure reduction No change

Number of patients

%

16 1 7 2

61.5 3.8 26.9 7.7

Number of patients (N = 26)

Cortical dysplasia Heterotopia DNET Granuloma Ganglioglioma Leukomalacia Polymicrogyria

20 1 1 1 1 1 1

DNET, Dysembryoplastic neuroepithelial tumor.

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TABLE 6. The relations between the diagnostic accuracy of presurgical evaluation and surgical outcome

TABLE 8. Magnetic resonance imaging diagnoses MRI findings

Presurgical evaluationa

Seizure free

Persistent seizure

p Value

10/16 7/16 8/16 3/12 13/16

3/10 3/10 3/9 4/7 5/10

0.113 0.391 0.317 0.182 0.580

Interictal EEG (26) MRI (26) PET (25) Ictal SPECT (19) Ictal scalp EEG (26)

Numbers of patients in parentheses. MRI, magnetic resonance imaging; SPECT, single-photon emission computed tomography; FDG-PET, fluorodeoxyglucose–positron emission tomography. a Focal abnormality compatible with intracranial ictal-onset zone.

results on diagnostic modalities are summarized in Tables 7 and 8. FDG-PET and ictal SPECT correctly lateralized the hemisphere in two and four patients, respectively, in addition to the correct localization. Of MRI findings, cerebromalacia and CD were the most common findings. Concordance of individual modalities Table 9 shows the concordance of interictal EEG, ictal scalp EEG, MRI, FDG-PET, and ictal SPECT according to surgical-outcome group. The concordance of all five modalities was not observed. The concordance of three or more modalities was observed in 10 of 16 seizure-free patients and in two of 10 non–seizure-free patients. It was significantly observed in those that achieved a seizure free status (p = 0.042; Fisher’s exact test). In those cases in which MRI localized the epileptogenic foci, PET was concordant in five patients, but ictal SPECT was concordant in only one. In those cases in which MRI did not localize the epileptogenic foci, PET localized the epileptogenic foci in three, and ictal SPECT localized the epileptogenic foci in two patients (Fig. 1). Lateralizing symptoms/signs and surgical outcome The presence of lateralizing symptoms or signs such as unilateral visual phenomenon or version was present in TABLE 7. Diagnostic sensitivities of individual modalities in seizure-free patients Diagnostic tool MRI (16) Ictal scalp EEG (16) Interictal EEG (16) FDG-PET (16) Ictal SPECT (12)

Number of patients

Normal Cerebromalacia Cortical dysplasia DNET Calcified mass Occipital infarction Ganglioglioma

12 5 5 1 1 1 1

Four patients had multiple or diffuse lesions on magnetic resonance imaging. DNET, Dysembryoplastic neuroepithelial tumor.

13 of 16 seizure-free patients and in five of 10 persistent seizure patients. No definite relation was found between the presence of lateralizing clinical seizure manifestation and surgical outcome (p = 0.108). DISCUSSION The typical elementary visual seizures of OLE are characterized by fleeting visual manifestations, which may be either positive or, less commonly, negative. Perceptive illusion also may occur (1,7,21). Twenty-two of the 26 patients in our series had a certain type of visual aura, which strongly suggests that the presence of a visual aura indicates OLE. However, only two patients had visual aura contralateral to the epileptogenic hemisphere, whereas others showed visual auras in the whole visual field. The location of visual manifestations was not helpful in the lateralization of seizure focus. The spreading pathway of occipital seizures was variable (8,22). If a seizure spreads to involve the temporal lobe, automatism and impaired consciousness can occur. An occipital seizure can spread to involve the suprasylvian convexity and create seizures mimicking supplementary sensory motor seizures or 2GTCSs. Nine patients in our series had experienced both automotor seizure and 2GTCSs at different times, which means that multiple spreading pathways can be present in a single patient. The most common problems encountered in evaluating patients with neocortical epilepsy for surgery include poor EEG localization of interictal spikes and seizure onset.

NonFalseLocalizing Lateralizing lateralizing localizing 7 13 10 8 3

1 0 2 4

9a 1 5b 2 2

1 1 4 4

MRI, magnetic resonance imaging; SPECT, single-photon emission computed tomography; FDG-PET, fluorodeoxyglucose–positron emission tomography. a Nine nonlateralizing MRI studies included seven normal images and two cases of multiple lesions. b No interictal spikes were detected in all five nonlateralizing interictal EEGs.


TABLE 9. Concordance of five diagnostic modalities (interictal EEG, ictal scalp EEG, magnetic resonance imaging, fluorodeoxyglucose–positron emission tomography, and ictal single-photon emission computed tomography) in the seizure-free and persistent-seizure groups Concordance 4 3 2 1 0

Seizure free (16)

Not seizure free (10)

2 8 4 2 0

1 1 4 4 0

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FIG. 1. Twenty-three-year-old male patient with the right occipital lobe epilepsy. The patient’s magnetic resonance imaging was normal. A: Fluorodeoxyglucose–positron emission tomography scans showed the right occipital hypometabolism. B: Interictal single-photon emission computed tomography (SPECT) demonstrated mild decreased perfusion in the right occipital area. C: Increased perfusion appeared in the right medial and lateral occipital areas. D: Subtraction SPECT also showed the predominant right occipital hyperperfused area.

These characteristics are major obstacles to the successful surgical treatment of this affliction (23–25), especially in those who do not show discrete lesions on MRI. Interictal EEG in OLE is frequently abnormal, but the apparent localization i not easy (8,24,26). Diffuse or bilateral distribution of interictal spikes may be observed. In our series, only half of the patients showed correctly localizing spikes or sharp waves. Ictal scalp recordings do not always suggest an occipital origin of the seizure because of rapid propagation to other lobes or to the contralateral occipital lobe. Ictal scalp EEG in our series correctly localized the epileptogenic lobe in 18 of the 26 patients, which represents a considerable localization rate. However, a selection bias may be present, because patients with a correct localization tend to be included for surgical treatment. The surgical treatment of OLE is now increasing. However, available data concerning the predictors of surgical outcome in this particular subgroup are somewhat limited. Therefore the identification of the clinical implications of neuroimaging modalities is important in the decision to adopt a surgical approach. Although it is difficult to compare MRI with FDG-PET or ictal SPECT, the localization of a lesion by MRI can both enhance confidence and provide more information than can FDG-PET or SPECT, especially when the localization is supported by an electrophysiologic study (27,28). MRI increases confidence in the localization of epileptogenic foci and allows surgical resection to be performed without preoperative invasive

studies. MRI also can be helpful at planning appropriate intracranial electrode placement. Thus imaging findings may favor surgery in some patients who otherwise might be rejected for surgery. However, our data do not clearly show the predictive value of a specific diagnostic modality, including MRI, on surgical outcome; the recruitment of a great number of patients may confirm the prognostic value of MRI or other diagnostic modalities concerning lesion localization. A higher-resolution T1 W 3D MRI with submillimeter isovoxel technique is the method of choice in the evaluation of CD. One of the reasons for a relatively low detection rate of CD in the study is likely the relatively thick section (1.5 mm instead of 40% of cases of nonlesional neocortical epilepsy (31), and in four of five focal CD patients with normal MRIs (32). When one considers that CD and other migrational disorders constitute a major proportion of the pathologic processes associated with epilepsy in the posterior areas of brain (33), FDG-PET may have both confirmative and independent diagnostic roles for the localization of epileptogenic foci. Ictal SPECT has been shown to be useful for defining the ictal-onset zone and for providing localizing information, even in patients with a normal MRIs (34,35), but it Epilepsia, Vol. 46, No. 5, 2005

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always requires an early injection and careful result interpretation, because rapid seizure propagation often leads to hyperperfusion in propagated areas. In our study, the sensitivity of ictal SPECT was not as high as previously reported. This may be related to several factors, such as differences in the injection time, patient populations, the natures of epileptogenic foci, and the rapidity of propagation. Because the different diagnostic methods rely on different physiologic mechanisms, the results of these diagnostic methods cannot be expected to be perfectly concordant. Neocortical epilepsy cases showed lower concordance rates than cases with mesial temporal lobe epilepsy, which can be explained by the lower sensitivities of all diagnostic methods in this group of patients (36–38). The concordance of different diagnostic methods means that the localized lesion reveals its abnormality through different physiologic mechanisms, which implies that a higher possibility exists of the colocalized lesion being an actual epileptogenic zone. Our data show that a successful surgical outcome can be expected when more than two diagnostic modalities are concordant in the localization of the epileptogenic focus. Ten of 12 patients with three or more concordant results became seizure free. However, the limited number of patients in our study who underwent surgical treatment may have caused the lack of clarity in our study results; studies on more patients are required to clarify this issue. In patients undergoing presurgical evaluations, functional neuroimaging may aid the confirmation of an occipital epileptogenic focus. In seizure-free patients with normal MRIs in our series, three of nine FDG-PET scans and two of seven ictal SPECT images correctly localized the epileptogenic zone, which are not high numbers. However, this result shows that diagnostic modalities may be complementary in term of the localization of the epileptogenic zone and make it possible to proceed with surgery in some patients. A lateralizing semiology has been reported to be a predictor of a good surgical outcome in the posterior cortex (39). However, our series could not show a definite relation between the presence of lateralizing signs/symptoms and surgical outcome, which had only marginal significance (p = 0.108). More patients should be recruited to draw a definite conclusion. Visual field defects increased or were newly developed postoperatively in most patients (21 patients). However, one patient did not show any visual field defect before or after occipital neocortical resection, and another patient with a previously small irregular field defect showed no increase of defect after occipital resection. This suggests that cortical reorganization may have occurred in some patients during lesion development. The pathologic diagnosis in both of these patients was CD (32,40). In conclusion, our study shows that the likelihood of a surgical outcome being favorable increases as the numEpilepsia, Vol. 46, No. 5, 2005

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