Comparative utility of technetium-99m hexamethylpropylenamine oxime single photon emission computed tomography (SPECT) with anatomic neuroimaging and electroencephalography (EEG) in childhood intractable epilepsy

Intractable epilepsies pose a therapeutic challenge. Precise localization of the epileptic focus is imperative before planning surgical intervention. Functional imaging is an important component of presurgical work-up. Positron emission tomography is unavailable in developing countries; hence, the need to evaluate the available imaging modality, single photon emission computed tomography (SPECT), was felt. We investigated 61 children with intractable epilepsy, identified by predefined criteria, by performing electroencephalography (EEG), magnetic resonance imaging (MRI), computed tomography (CT), and ictal and interictal SPECT. The localizing value of ictal and interictal SPECT imaging for epileptic foci was correlated with clinical, electrophysiologic, and anatomic neuroimaging data. An ictal SPECT was obtained in 9, and interictal SPECT was performed in all (61). Ictal SPECT was localizing in 8 of 9 (88.8%). Interictal SPECT was localizing in a significantly higher proportion of patients (47.54%) than either the scalp EEG (16.39%) (P = .0003) or CT scan (21.56%) (P = .0046). Our data demonstrated that interictal and ictal SPECT identified more focal changes in children with intractable epilepsy than interictal EEG, CT, and probably MRI. The definitive proof of the SPECT-based findings being epileptogenic foci awaits correlation with intraoperative monitoring and postoperative follow-up.     

Ictal single-photon emission computed tomography demonstrates localized epileptogenesis in cortical dysplasia

We investigated the use of ictal single-photon emission computed tomography (SPECT) in 2 children with intractable epilepsy. Ictal scalp electroencephalographic studies failed to localize the epileptic focus and interictal data demonstrated widespread lateralized abnormalities. Ictal SPECT studies with technetium 99m–hexamethylpropyleneamineoxime demonstrated focal areas of hyperperfusion in the frontal lobes. Resection of the abnormal areas shown by SPECT was carried out despite evidence of large areas of epileptogenesis demonstrated by scalp and subdural electroencephalographic studies. Pathological material revealed cortical dysplasia. Ictal SPECT provides functional evidence for localized epileptogenesis in focal cortical dysplasia.     

Comparison of modern diagnostic methods in children with intractable focal epilepsy

The basic aim of neuroimaging in children with intractable focal epilepsy is stablishing localization of epileptogenic zone. In this study 34 children (age 11-17 years) with intractable focal epilepsy were examined including: clinical history, physical examination, EEG, CT, MR, 99mTc-HMPAO SPECT. The hypoperfused region in interictal SPECT was concordant with clinical seizure characteristics in 22 children, with EEG in 13, with MR with 13 children. The localization of hyperperfused region in ictal SPECT was concordant with the clinical seizure characteristics in 9 from 10 examined children, with EEG in 7 and with MR in 8. The diagnostic value of estimation of the localization of epileptogenic zone in interictal SPECT (63 per cent) was comparable with the results of EEG (56 per cent) and MR (59 per cent), but ictal SPECT offers more information (100 per cent). In conclusion, performing both ictal and interictal SPECT studies may provide data about both seizure origin and its relationship with structurally abnormal regions of the brain.     

Fluctuations of interictal brain imaging in repeated 123I-IMP SPECT scans in an epileptic patient

Summary Single photon emission computed tomography (SPECT) brain scans with N-isopropyl-(iodine 123) p-iodoamphetamine (¹²³I-IMP) were performed three times in interictal periods in a 35-year-old man with intractable frontal lobe epilepsy and normal X-ray CT findings. The first scan showed decreased ¹²³I-IMP uptake in the right frontal lobe. This abnormal image was regarded as the primary focus of his epilepsy on the basis of its regional agreement with focal epileptic discharges on EEGs. In the second scan, he showed normal imaging, while the third scan showed the same abnormal image as before, in the right frontal lobe. The frequency of his clinical seizures was almost unchanged during the intervals between scans and further EEGs recorded soon after each scan showed almost no changes in the basic activities and frequency of the epileptic discharges. Such fluctuations in SPECT brain imaging suggest that the severity of functional inactivation underlying the focal hypoperfusion image as an epileptic focus may fluctuate considerably in the interictal state with no relation to the clinical features of epilepsy.     

Ictal cerebral perfusion related to EEG in drug resistant focal epilepsy of childhood.

OBJECTIVES: To evaluate the EEG changes during seizures in children with drug resistant focal epilepsy who demonstrate hypoperfusion at the "seizure focus" interictally, but no perfusion change during the seizure. METHODS: Ictal EEG findings of six children with focal epilepsy who demonstrated hypoperfusion on rCBF SPECT after an interictal injection of (99)Tc(m) HMPAO concordant with the seizure focus, but who did not demonstrate rCBF change after an ictal injection (group 1) were reviewed. These were contrasted with the EEG data of six children matched as closely as possible for age, type of epilepsy, and pathology who did show hyperperfusion at the seizure focus on ictal scan when compared with the interictal study (group 2). RESULTS: The children in group 1 showed slowing of the EEG at the time of the (99)Tc(m) HMPAO injection relative to that seen at the onset of the seizure. Those in group 2 showed rhythmic activity, or sharp waves, or both on EEG at the time of injection. This last change was also seen consistently when the EEG data of a further 13 children who also showed ictal hyperperfusion at the seizure focus were reviewed. CONCLUSION: Ictal rCBF does not invariably increase at the seizure focus in patients with drug resistant focal epilepsy.     

Ictal 99mTc-HMPAO Single Photon Emission Computed Tomography in Children with Temporal Lobe Epilepsy

Seventeen ictal ^99mTc-HMPAO single photon emission computed tomography (SPECT) studies were performed in 15 children with temporal lobe epilepsy (TLE) aged 7–14 years (mean 10.3 years). Ictal SPECT was informative in 16 of 17 (94%) studies in 14 of 15 (93%) children, showing unilateral temporal lobe hyperperfu sion. In all 16 informative ictal SPECT studies, lateral-ization was concordant with ictal EEC, magnetic resonance imaging (MRI), and pathology. In 4 children, ictat SPECT provided additional localizing information that was not apparent from concurrent ictal EEC recording. Blinded interpretation of ictal SPECT studies by two independent investigators showed correct lateralization of the epileptic focus in every child. Results of visual analysis of ictal SPECT images were corroborated by quantitative analysis. Although interictal SPECT studies showed a degree of temporal lobe hypoperfusion in all children, in 9 of 15 hypoperfusion was either minimal, bilateral, contralateral, or associated with extratemporal hypoperfusion. In children with TLE, ictal SPECT provides reliable lateralizing information to corroborate or supplement that obtained from surface EEG and MRI.     

SPECT measurements with 99mTc-HM-PAO in focal epilepsy

The ability of SPECT measurements with [99mTc]-HM-PAO (Ceretec) to find the location of the epileptic focus was studied in patients under consideration for neurosurgical treatment for therapy-resistant focal epilepsy. The location of low [99mTc]-HM-PAO uptake regions found at interictal measurements, and of high [99mTc]-HM-PAO uptake regions found at ictal measurements, was compared to the findings of extensive ictal and interictal EEG examinations, and to the results of CT and MRT. While EEG revealed focal epileptic activity in all of the 14 patients, SPECT showed regional abnormalities in 13 (93%). CT and MRT showed abnormal findings in 30%.     

Correlation of ictal EEG and SPECT studies in patients of intractable epilepsy with normal MRI

Identification of the epileptic focus is the most important requirement for a successful surgical outcome in intractable epilepsy. Patients with normal MRI on high-resolution imaging pose a significant challenge in this regard. We tried to identify the epileptic focus using interictal / ictal SPECT and ictal EEG patterns in 14 patients with normal MRI. Rhythmic ictal onset activity helped to identify a single focus in 10 patients (71.43%). Inter ictal SPECT detected a focus corresponding to ictal EEG in 6 out of 10 patients (60%) in whom the test was performed. Ictal SPECT done in 5 patients correctly identified the focus in all patients (100%). Our data indicate that it is possible to obtain localization in patients with normal MRI using a combination of ictal EEG patterns and an ictal SPECT study.     

Correlation Between Interictal Regional Cerebral Blood Flow and Depth-Recorded Interictal Spiking in Temporal Lobe Epilepsy

Summary: Purpose: Single photon emission computed tomography (SPECT) is used as an adjunctive method in preoperative localization of epileptic foci. In temporal lobe epilepsy (TLE), interictal hypoperfusion is observed in 60–70% of cases. Correlation with ictal EEG changes is observed in ～50–60% of cases. Relationships with interictal EEG have been studied less. We compared interictal SPECT data obtained in 20 patients with their interictal intracerebral electrical activity recorded by depth electrodes to evaluate a potential relationship. Methods: We studied 20 sequential patients whose clinical, surface, and depth EEG data indicated seizure originating in the temporal lobe and who had interictal [^99mTc]hexamethyl-propylene amine oxime (HMPAO)-SPECT stereo-EEG (SEEG). Intracerebral electrodes were placed according to the patient's profile. The interictal extent of epileptiform activity allowed delineation of the irritative zone. Interictal spike frequency was also analyzed semiquantitatively. Visual and numerical SPECT analysis was performed blind to SEEG data. Results: Interictal hypoperfusion was observed in 16 patients, involving the epileptogenic temporal lobe in 14. Except for 1 patient who manifested lateral temporal hypoperfusion corresponding to a mass lesion, two distinctive patterns of hypoperfusion were noted: (a) mesial hypoperfusion (5 patients), and (b) global temporal hypoperfusion (8 patients). In 8 patients, hypoperfusion had also extended into the adjacent cortex. Temporal mesial hypoperfusion was associated with spiking limited to the mesial structures, whereas global temporal hypoperfusion or hypoperfusion extending beyond the temporal lobe was associated with a similar topographic pattern of spikes. Conclusions: Comparison between SPECT and SEEG data collected in the interictal phase indicated that the extent of the hypoperfused area correlated topographically with that of the underlying irritative zone.     

Changes in Regional Cerebral Blood Flow Beyond the Temporal Lobe in Unilateral Temporal Lobe Epilepsy

Summary: Purpose: Single photon emission computed tomography (SPECT) is widely used to evaluate functional abnormalities during the epileptic event. Changes in regional cerebral blood flow (rCBF) are well defined in patients with temporal lobe epilepsy (TLE) undergoing surgical resection. Nonetheless, the interpretation of ictal abnormalities in CBF beyond the temporal lobes has not been carefully addressed.
Methods : We assessed 4 patients with pathologically proven unilateral TLE who had significant ipsilateral frontal hypoperfusion in ictal studies with no other abnormalities but chronic epilepsy accounting for such findings. Patients were assessed as candidates for surgery by interictal EEG, neuropsychological studies, brain magnetic resonance imaging, scalp electrode video-EEG monitoring, and ictal SPECT.
Results : Characteristic hyperperfusion was evident over the temporal lobe ipsilateral to the EEG focus, with significant hypoperfusion over the frontal region in 3 patients. In patient 4, frontal hypoperfusion was not statistically significant.
Conclusions : SPECT demonstrated relative rCBF changes beyond the epileptogenic zone in unilateral TLE. Our findings provide further insight into the pathophysiological changes underlying this condition.     

Ictal and interictal ECD-SPECT for focus localization in epilepsy

Forty-one ECD (Technetium-99m-ethyl cysteinate dimer) SPECT investigations were undertaken in the course of a presurgical diagnostic work-up in 23 patients with pharmacoresistant focal epilepsy. In 21 patients, both an ictal and interictal SPECT were conducted. In the patients receiving ictal SPECT the tracer was injected between 7 and 30 s after the seizure onset. Of the interictal SPECTs 17 of 23 showed focal hypoperfusion which was consistent in 17 cases (74%) with the area of the electrophysiological focus (EF) and 6 patients had a normal interictal SPECT. Of the ictal SPECTs 18 of 21 (86%) showed regional hyperperfusion, 18 of them in the same location as the EF. Ictal SPECT showed a hypoperfusion similar to that in interictal SPECT in another 3 patients. In these cases seizure duration was short (28–54 s), so that the tracer reached the brain postictally. Our results show that ictal ECD-SPECT is an effective method for demonstrating an epileptogenic focus. Possible reasons for false-negative ictal SPECT results are discussed.     

Utility of interictal SPECT of rCBF for focal diagnosis of the epileptogenic zone(s)

With Single Photon Emission Computed Tomography (SPECT) of regional cerebral bloodflow (rCBF) ictally and interictally, regional changes of rCBF can be detected in many cases with medically intractable complex partial seizures. Interictal SPECT shows abnormal rCBF in the epileptogenic temporal lobe in 40% to 85% of the patients. A critical survey of the methodological problems considering isotopes, scanners, data analysis and patient population is presented here as well as a few semi-quantitative studies including our own. It is concluded, that SPECT of rCBF is a useful, non-invasive method of localizing the epileptogenic zone in patients with severe partial focal epilepsy. Ictal SPECT of rCBF has a higher predictive value and is more sensitive than interictal studies for localization of the seizure focus. Interictal SPECT using a high-resolution system obtains an almost as high frequency of localization of the focus. With low resolution scanners, a minor frequency is observed. Both interictal and ictal SPECT recordings should be obtained for localization of the epileptogenic focus in presurgical cases as interictal hypoperfusion and ictal hyperperfusion demonstrated in the same focal area are highly characteristic of a seizure focus.     

Electrical source imaging for presurgical focus localization in epilepsy patients with normal MRI

Purpose: Patients with magnetic resonance (MR)–negative focal epilepsy (MRN‐E) have less favorable surgical outcomes (between 40% and 70%) compared to those in whom an MRI lesion guides the site of surgical intervention (60–90%). Patients with extratemporal MRN‐E have the worst outcome (around 50% chance of seizure freedom). We studied whether electroencephalography (EEG) source imaging (ESI) of interictal epileptic activity can contribute to the identification of the epileptic focus in patients with normal MRI. Methods: We carried out ESI in 10 operated patients with nonlesional MRI and a postsurgical follow‐up of at least 1 year. Five of the 10 patients had extratemporal lobe epilepsy. Evaluation comprised surface and intracranial EEG monitoring of ictal and interictal events, structural MRI, [¹⁸F]fluorodeoxyglucose positron emission tomography (FDG‐PET), ictal and interictal perfusion single photon emission computed tomography (SPECT) scans. Eight of the 10 patients also underwent intracranial monitoring. Results: ESI correctly localized the epileptic focus within the resection margins in 8 of 10 patients, 9 of whom experienced favorable postsurgical outcomes. Discussion: The results highlight the diagnostic value of ESI and encourage broadening its application to patients with MRN‐E. If the surface EEG contains fairly localized spikes, ESI contributes to the presurgical decision process.     

Ictal and Interictal Single Photon Emission Computed Tomography in a Patient With Benign Familial Infantile Convulsions

Ictal and interictal single photon emission computed tomography (SPECT) and ictal electroencephalography (EEG) were studied in a 3-month-old girl with benign familial infantile convulsions (BFIC) to reveal the epileptic focus. There was bilateral diffuse propagation from a left frontal lobe focus on the ictal EEG. Perfusion in the left frontal region was increased on ictal SPECT and decreased on interictal SPECT. Epileptic foci of BFIC showed the same characteristics as foci of symptomatic partial epilepsy.     

Localizing value of alpha-methyl-L-tryptophan PET in intractable epilepsy of neocortical origin.

BACKGROUND: [(11)C] alpha-methyl-L-tryptophan (alpha-MTrp) has been developed as a tracer for the study of the synthesis of serotonin in the brain with PET. However, it has been shown that in pathologic conditions the tracer may reflect the activation of kynurenine metabolism. Increased levels of serotonin and quinolinic acid have been described in resected epileptogenic cortex, raising the possibility that alpha-MTrp can localize seizure foci in patients with intractable partial epilepsy. The authors assessed the uptake of alpha-MTrp in 18 patients (11 men, mean +/- SD age 27.1 +/- 10.1 years, range 13 to 54) with intractable partial epilepsy to correlate the PET findings with the epileptogenic area defined by electroclinical and neuroimaging data. METHOD: Seven patients with cortical dysplasia (CD) and 11 with partial epilepsy in which conventional MRI and fluorine-18-deoxyglucose ((18)FDG)-PET studies failed to detect any abnormality were studied. All underwent scalp EEG monitoring during the PET scan to exclude ictal events and estimate the interictal epileptic activity. RESULTS: In seven patients (39%; CD four and cryptogenic partial epilepsy three), PET showed focal increased uptake of alpha-MTrp corresponding to the epileptogenic area. alpha-MTrp uptake in the epileptic focus correlated with the frequency of interictal spikes (r = 0.7, p < 0.05). CONCLUSIONS: alpha-MTrp-PET may be of value in the localization of the epileptogenic area not only in patients with visible dysplastic lesions, but also in those with cryptogenic partial epilepsy.     

Ictal brain imaging in presurgical evaluation of patients with medically intractable complex partial seizures

At the Indiana University Medical Center, 99 patients with medically intractable complex partial seizures (MI-CPS) had presurgical evaluation with subsequent anterior temporal lobectomy. The majority of the patients had single photon emission tomography (SPECT) performed interictally as well as during an actual epileptic seizure (ictal scan). Decreased regional cerebral perfusion (rCP) was seen in 54/94 (57%) of the interictal scans corresponding to the eventual site of the surgery. However, ictal scans provided a higher yield; increased rCP in the temporal lobe during an actual seizure was observed in 60/82 (73%) concordant to the side of surgery. SPECT is a useful, noninvasive method of localizing the epilepti-form focus in patients with MI-CPS considered for resective surgery. Both interictal and ictal SPECT need to be performed; combined interictal hypo-perfusion and ictal hyperperfusion in the same focal area are unique to epileptogenic lesions. Ictal SPECT studies can be performed in the majority of patients during the period of continuous video/EEG monitoring with only a little additional effort. Combining the results of functional brain imaging (interictal and ictal SPECT, PET) with clinical semiology of seizures, surface and sphenoidal EEG, magnetic resonance imaging and other non-invasive tests, anterior temporal lobectomy can be recommended in approximately two-thirds of the patients without resorting to potentially dangerous intracranial EEG monitoring.     

Interictal PET and ictal subtraction SPECT: Sensitivity in the detection of seizure foci in patients with medically intractable epilepsy

Purpose: Interictal positron emission tomography (PET) and ictal subtraction single photon emission computed tomography (SPECT) of the brain have been shown to be valuable tests in the presurgical evaluation of epilepsy. To determine the relative utility of these methods in the localization of seizure foci, we compared interictal PET and ictal subtraction SPECT to subdural and depth electrode recordings in patients with medically intractable epilepsy. Methods: Between 2003 and 2009, clinical information on all patients at our institution undergoing intracranial electroencephalography (EEG) monitoring was charted in a prospectively recorded database. Patients who underwent preoperative interictal PET and ictal subtraction SPECT were selected from this database. Patient characteristics and the findings on preoperative interictal PET and ictal subtraction SPECT were analyzed. Sensitivity of detection of seizure foci for each modality, as compared to intracranial EEG monitoring, was calculated. Key Findings: Fifty‐three patients underwent intracranial EEG monitoring with preoperative interictal PET and ictal subtraction SPECT scans. The average patient age was 32.7 years (median 32 years, range 1–60 years). Twenty‐seven patients had findings of reduced metabolism on interictal PET scan, whereas all 53 patients studied demonstrated a region of relative hyperperfusion on ictal subtraction SPECT suggestive of an epileptogenic zone. Intracranial EEG monitoring identified a single seizure focus in 45 patients, with 39 eventually undergoing resective surgery. Of the 45 patients in whom a seizure focus was localized, PET scan identified the same region in 25 cases (56% sensitivity) and SPECT in 39 cases (87% sensitivity). Intracranial EEG was concordant with at least one study in 41 cases (91%) and both studies in 23 cases (51%). In 16 (80%) of 20 cases where PET did not correlate with intracranial EEG, the SPECT study was concordant. Conversely, PET and intracranial EEG were concordant in two (33%) of the six cases where the SPECT did not demonstrate the seizure focus outlined by intracranial EEG. Thirty‐three patients had surgical resection and >2 years of follow‐up, and 21 of these (64%) had Engel class 1 outcome. No significant effect of imaging concordance on seizure outcome was seen. Significance: Interictal PET and ictal subtraction SPECT studies can provide important information in the preoperative evaluation of medically intractable epilepsy. Of the two studies, ictal subtraction SPECT appears to be the more sensitive. When both studies are used together, however, they can provide complementary information.     

Usefulness of Ictal and Interictal 99mTC Ethyl Cysteinate Dimer Single Photon Emission Computed Tomography in Patients with Refractory Partial Epilepsy

Summary: Purpose: Ictal perfusion single photon emission computed tomography (SPECT), using HMPAO, has been shown to localize epileptic foci in ～90% of studies. Unfortunately, HMPAO decomposes rapidly, precluding the performance of ictal studies. Ethyl cysteinate dimer (ECD) is a SPECT perfusion agent recently approved by the Food and Drug Administration. After preparation, this compound is stable for ～6 h. facilitating the performance of ictal studies. Methods: In a prospective, open-label, uncontrolled, non randomized study, we evaluated the potential benefits of the use of ^99mTc-ECD SPECT for lateralization of the epileptic focus. Ten consecutive adult epilepsy surgery candidates were studied with ictal and interictal ^99mTc-ECD SPECT. Results: The mean delay between seizure onset and ictal SPECT injection was 23.2 s. The mean seizure duration was 84.1 s. Ictal studies agreement between the epilepsy focus and area of hyperperfusion was evident in 8 of 10 cases. In one case, SPECT was lateralized in a patient with bilateral temporal lobe epilepsy (TLE); however, hyperperfusion was observed on the same side of that particular seizure. In another case, there was location disagreement. Interictal SPECT showed focal hypoperfusion in three cases. Conclusions: ^99mTc-ECD proved to be an optimal tracer for ictal studies. Although this is a small series, the results of ictal and interictal findings using 99mTc-ECD are similar to those reported with ^99mTc-HMPA0. Because ^99mTc-ECD has a longer decomposition time, true ictal studies are easier to obtain. This new tracer will probably allow the use of ictal SPECT to become widely accepted in most epilepsy centers.     

Neuronal migrational disorders in children with epilepsy: MRI,interictal SPECT and EEG comparisons

Single-photon emission computed tomography (SPECT) is being increasingly used in the investigation of children with epilepsy and may provide insights into congenital malformations. We analyzed the interictal⁹⁹Tc-HMPAOSPECT in a series of seven children with developmental disorders of the neocortex, each of them representing a prototype of cerebral dysgenesis, such as lissencephaly, pachygyria, opercular dysplasia, polymicrogyria, nodular heterotopia and band heterotopia. The patients studied were selected among 22 epileptic children with neuronal migrational disorders (NMDs). Interictal SPECT hypoperfusion was observed in the area homologous to MRI findings in all the examined children. In three patients low perfusion was also present in the opposite hemisphere, probably due to functional involvement or related to an underlying microdysgenesis, not revealed by structural imaging. EEG features were in agreement with low perfusion areas, both anatomically and functionally, in all children. In one patient hypoperfusion area differed from that revealed by MRI and EEG. Ictal SPECT has been considered a useful tool for accurately locating the epileptic focus. Nevertheless, interictal brain perfusion studies, together with proton magnetic resonance spectroscopy, may play an important role in detecting anatomic substrate in developmental disorders of the neocortex.     

Comparative study of interictal PET and ictal SPECT in complex partial seizures

Objective – To compare the sensitivity of ictal ^99mTc-HMPAO single photon emission computed tomography (SPECT) with interictal ¹⁸F-fluorodeoxyglucose positron emission tomography (PET) in localization of the epileptogenic focus in patients with medically intractable complex partial seizures (MI-CPS). Material and methods – Retrospective analysis was performed on patients with MI-CPS who underwent anterior temporal lobectomy from January 1993 onwards when PET became available to us for clinical studies at the Indiana University Medical Center. There were 38 female and 29 male patients (total=67) with MI-CPS, 10 to 55.5 years of age (mean 31) and duration of their epilepsy from 1-46 years (mean 21). Interictal PET was evaluated for evidence of focal hypometabolism and ictal SPECT for focal perfusion abnormality (hyperperfusion or hypoperfusion) by visual analysis. Results – Both Ictal SPECT and interictal FDG-PET studies were obtained in 36 patients with MI-CPS. PET showed definite hypometabolism in 30 and questionable hypometabolism in an additional two patients. Ictal SPECT correctly localized the seizure focus in 27 patients by demonstrating ictal hyperperfusion whereas in one the hyperperfusion was falsely localized. In an additional seven patients the ictal SPECT provided probable localization by demonstrating ictal hypoperfusion in the appropriate temporal lobe. The sensitivity of ictal SPECT and interictal PET was 34/36 and 32/36, respectively, the difference was not statistically significant (χ²_y=0.18, DF=1, P=0.67). In six of the 36 patients the two tests were complementary to each other in providing localizing information. Conclusion – Ictal SPECT and interictal PET are equally sensitive and reliable techniques in localizing the epileptogenic focus in patients with MI-CPS. They play a critical role in providing localization in MRI negative patients allowing surgical resection to be undertaken in many without additional invasive electrographic monitoring.