11Journal ofNeurology, Neurosurgery, and Psychiatry 1990;53:11-15

CT, MR and SPECT imaging in temporal lobeepilepsy

Roderick Duncan, James Patterson, DonaldM Hadley, Peter Macpherson,Martin J Brodie, Ian Bone, Anne P McGeorge, David J Wyper

AbstractCranial computed tomography (CT) withmodified temporal lobe technique, 0-15Tmagnetic resonance imaging (MRI) andsingle photon emission computedtomography (SPECT) were carried outon 30 patients with intractable temporallobe epilepsy. Lateralising abnormalitieswere detected in 21/30 patients overall.Specific lesions were detected by CT inone patient and by MRI in seven patients(in one case bilateral). In addition CTdetected asymmetry of the sylvian fis-sures or temporal horns in 10 patients,and MRI in eight patients. SPECT detec-ted lateralising abnormalities in 19patients (in five cases bilateral). It isconcluded that low field MRI is superiorto modified CT in demonstrating subtlestructural lesions of the temporal lobe.Functional scanning with SPECT sup-ports the evidence oforigin ofan epilepticfocus in a substantial proportion of casesand may improve the selection ofpatientsfor surgery.

Institute ofNeurological Sciences,Southern GeneralHospital, GlasgowR DuncanJ Patterson,D M HadleyP MacphersonM J BrodieI BoneA P McGeorgeD J WyperCorrespondence to:Dr R Duncan,Institute of NeurologicalSciences,Southern General Hospital,Govan Road,Glasgow G51 4TF, Scotland

Received 10 March 1989 andin revised form 6 July 1989.Accepted 19 July 1989.

Temporal lobe epilepsy is the commonest formof epilepsy encountered and is often refractoryto drug therapy; the prevalence rate of suchrefractory epilepsy may be as high as 80-90/100,000 in the general population.' Temporallobectomy is increasingly recognised as an

effective treatment, giving good results in 70-80% of patients, with low morbidity and mor-

tality.23 Its use has been restricted to a greatextent by the complex and time consumingelectrophysiological testing often required tolateralise the focus. New imaging techniques,however, may detect lateralising abnormalities,improving selection for surgery.

MethodsSubjectsThe subjects were 30 patients (16 male, 14female) seen sequentially at two outpatientclinics in the city of Glasgow. Their agesranged from 13-47 (mean 27.9) years. Theduration of seizure disorder ranged from 2-29(mean 14-8) years and the age at onset was from1-26 (13-3) years. The inclusion criteria for thestudy were a definite clinical diagnosis oftemporal lobe epilepsy and intractability. Theformer required both the absence (stare com-bined with impaired awareness and responsive-ness), and features of temporal lobeinvolvement in the aura, such as deja vu, or in

the seizure itself, such as automatism. Thelatter required that seizure control be unsatis-factory despite optimal drug treatment."Unsatisfactory" seizure frequency in thisstudy ranged from one per fortnight to five perday. This depended on the occupation, socialcircumstances and expectations of the patient,the manifestations of the seizures themselves(brief absences being, for example, bettertolerated than prolonged automatisms), and theduration of post ictal effects. The patients hadall been tried on three major anticonvulsantdrugs, separately or in combination, all withconcentrations within their respective targetranges.

Scanning procedureThe patients were assessed clinically and scan-ned in hospital as day cases.

HM-PAO SPECTHM-PAO is a lipophilic amine. It crosses theblood-brain barrier freely, and 85% of brainuptake occurs on the first pass after anintravenous injection. Once inside the braintissue, it forms a hydrophilic compound. Thiscan only slowly recross the blood-brain barrierand so its pattern of distribution in the brain,and that of the technetium 99m with which it islabelled, reflects the amount delivered andhence rCBF at the time of the first pass afterintravenous injection. The activity in braintissue remains essentially constant for severalhours,4 allowing a delay before scanning. SincerCBF correlates closely with regional cerebralmetabolism in epilepsy,5 HM-PAO SPECTeffectively images both.The patients were injected intravenously

with 500MBq of Tc99m labelled HM-PAOduring EEG recording using the standard 10/20 system of electrode placement. The timesince the last seizure was recorded at the time ofinjection. All were scanned within one hour ofinjection using a Novo 810 tomographicimager, producing 12 mm axial sectionsparallel to the orbito-meatal line. The resolu-tion of this system is less than 1 cm, and theimages are comparable to those of mostpositron emission tomography (PET) systemscurrently in use.The SPECT images were interpreted

independently by a clinician (RD), a radiologist(DMH) and a physicist (JP), blind to any dataother than the diagnosis of temporal lobeepilepsy. Differences were resolved by consen-sus conference. The perfusion ofeach temporallobe was compared not only with the con-tralateral temporal lobe, but also with the

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Duncan, Patterson, Hadley, Macpherson, Brodie, Bone, McGeorge, Wyper

Table Summary of results of CT, MRI and SPECT

CT MRI SPECT

Normal 19 17 11Lateralising lesion shown 1 7 19Asymmetry of sylvian fissure or temporal horn shown 10 8 -

Bilateral abnormalities shown 0 1 5

Figure 1 Venn diagramshowing the numbers ofpatients showing specificabnormalities on CT,MRI and SPECT. Theareas of intersectionbetween circles representpatients with lesionsshowing on more than oneimaging modality.

frontal and occipital lobes, allowing the distinc-tion to be made between hypoperfusion of onetemporal lobe and hyperperfusion of the other.Based on data from 10 normal volunteers, our

upper limit of normal for side-to-side dif-ference is 7%. This is in agreement with datafrom other centres using the same technique.6

CT and MRICT was carried out using a Phillips 350Tomoscan, producing axial 6 mm sections ofthe whole brain, together with axial 6 mmtemporal lobe sections angled parallel to thetemporal horns, the latter cuts repeated after50 ml (300 mg/ml iodine) of intravenous con-

trast medium.MRI was performed using a Picker 0-15T

resistive imager, producing 8 mm axial

SE 2000/80 T2 weighted images of the wholebrain, axial 8 mm IR TI weighted 1660/400/40images of the temporal lobes, and coronal5 mm balanced SE 700/32 images of the tem-poral lobes.CT and MR images were interpreted and

reported independently by two investigators(DMH and PM), blind to any data other thanthe diagnosis of temporal lobe epilepsy. Dis-agreements between reports were resolved byconsensus conference.

ResultsThe results of CT, MRI and SPECT aresummarised in table 1. Lateralising abnor-malities were seen in 21/30 patients overall, in15/21 unilateral and in 6/21 bilateral. Thecorrespondence between the imagingmodalities is illustrated by a Venn diagram infig 1.

CTCT detected a specific lateralising abnormalityin only one patient, a small area of calcificationin the temporal lobe (fig 2). In a further 10 casesvarying degrees of asymmetry of the temporalhorns or sylvian fissures was apparent.

MRIMRI detected specific lateralising abnor-malities in seven patients. Areas of abnormalsignal compatible with oedema, gliosis ortumour were detected in the medial temporallobe in two patients (fig 3) and in the temporalpole in one patient. In one further patient asimilar lesion in the medial temporal lobe wasaccompanied by an increase in signal through-out the contralateral temporal lobe. In twopatients an increase in signal throughout onetemporal lobe was seen as an isolated finding.In one patient a lesion compatible with anarteriovenous malformation or haemartomawas seen in the medial temporal lobe. In eightpatients varying degrees of asymmetry of thetemporal horns or sylvian fissures were seen.

Figure 2 A 23 year oldman with frequent complexpartial seizures. (a) CTshowing punctate focus ofcalcification in the whitematter of the righttemporal lobe. (b) T2weighted (SE 2000/80)MRI section showing thesame lesion as ahypointense focussurrounded by an area ofhyperintensity.

SPECT

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CT, MR and SPECT imaging in temporal lobe epilepsy

Figure 3 A 29year oldwoman with severecomplex partial andsecondary generalisedseizures. (a) SPECT 3hoursfollowing a seizureshowingfocalhyperperfusion in themedial left temporal cortex(arrow). (b) T2 weighted(SE 2000/80) MRIsection showing thehyperperfused lesion as anarea of hyperintensitywhich is slightly spaceoccupying. Anatomicalasymmetry betweentemporal lobes is alsoshown.

Comparison of CT and MRIMRI failed to detect calcification in one lesiondetected by CT, but did detect the lesion as anarea of high signal with a central area of lowsignal. Otherwise MRI detected lesions in sixpatients which were missed by CT.

SPECTSPECT detected abnormalities in 19 patients.In 10 this consisted ofunilateral hypoperfusionconfined to the temporal lobe (fig 4). In one ofthese patients an immediately post ictal scanshowed an area of hyperperfusion at the samesite.

In two patients temporal hypoperfusionextended into the frontal lobe. In one patient

there was unilateral frontal hypoperfusion, inone patient bilateral frontal hypoperfusion andin one patient bilateral temporal hypoper-fusion. In three patients temporal hypoper-fusion was accompanied by contralateral tem-poral hyperperfusion. In one patient who had aseizure several minutes before injection ofHM-PAO, SPECT showed temporal hyper-fusion extending into the frontal lobe (fig 5).

Comparison of SPECT with CT and MRI(comparison of "functional" with "structural"scans)SPECT detected abnormalities in 14 patientsin whom CT and MRI were normal, or showedonly anatomical asymmetry. In seven of these

Figure 4 A 13 year oldboy with intractablecomplex partial andsecondary generalisedseizures. (a) InterictalSPECT showinghypoperfusion of the righttemporal lobe. (b) Tiweighted (IR 1400/400/40) MRI section showingminimal enlargement ofthe right sylvianfissure(arrow).

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Duncan, Patterson, Hadley, Macpherson, Brodie, Bone, McGeorge, Wyper

Figure 5 A 29year oldwoman with intractablecomplex partial seizures.(a) SPECT5 hoursfollowing a seizure showingmarked asymmetryrepresentinghyperperfusion of the lefttemporal andfrontalcortex. (b) Balanced (SE700/32) coronal MRIsection through thefrontaland mid temporal lobesshowing no anatomicalabnormality.

patients the abormalities were unilateral. Intwo cases lateralising abnormalities were seenon CT or MRI which were not accompanied byabnormalities of regional cerebral perfusion.There were no cases where CT or MRI

showed a definite lesion on one side andSPECT lateralised to the other, although therewas one patient who showed CT and MRIenlargement ofone temporal horn, but SPECTshowed hypoperfusion of the contralateraltemporal lobe. EEG lateralisation agreed withSPECT in this case.

Correlation of CT, MRI with SPECT withsurface EEGMultiple surface EEG recordings (includingsleep or activated recordings in three cases,ictal recordings in three cases and sphenoidalrecordings in one case) gave consistent lateral-isation in 17 patients. There were lateralisingabnormalities on CT, MRI or SPECT in 10 ofthese patients. Lateralisation agreed in all casesbut one, where EEG lateralisation disagreedwith lateralisation based on temporal hypoper-fusion seen on SPECT. In three cases, SPECTshowed hypoperfusion with hyperperfusion inthe contralateral temporal lobe. In all three,EEG lateralised to the hypoperfused side andin two of these cases MRI also showed abnor-malities on the hypoperfused side. In both thelatter the hypoperfused temporal lobe wasremoved, with good results.

DiscussionSeveral reports have shown the superiority ofMRI over CT in detecting lateralising lesionsin temporal lobe epilepsy.7'2 These studiescompared MRI using field strengths of 0 35-1-5 T, and CT using standard axial sectionswith or without contrast. This study makes adifferent comparison; that of low field (0 15 T)MRI (most commonly available in the UnitedKingdom) and of CT with temporal lobe cuts

angled to image temporal lobe structures to thebest effect. Nonetheless, the difference be-tween the results obtained using the two imag-ing modalities was the same; MRI is moresensitive in showing subtle lesions of temporallobe structures, with the minor exception ofsmall areas of calcification, which are bettershown by CT. It is difficult to make directcomparisons in terms of the abnormality rate,but most studies show an MRI abnormalityrate of 20-25% in patients with normal CT7"0whatever the field strength of the MR imager,with the interesting exception of one studycomprising only well controlled patients whichshowed an abnormality rate of just over 5000.11One retrospective study of patients who hadhad temporal lobectomy found abnormalitiesin 65% of patients with normal CT, but somepatients had CT using low resolution equip-ment.'2 Only one study found any lesion detec-ted by CT and not by MRI,7 a small fleck ofcalcification.

In this study CT was marginally more effec-tive in showing anatomical asymmetry.However, in those patients in whom asym-metry was marked (six cases), it was shown byboth investigations. In those in whom asym-metry was shown by only one investigation (byMRI in two cases and by CT in four cases), thedegree was minor and of little value as alateralising finding.

Interictal studies in temporal lobe epilepsyusing both positron emission tomography(PET) and SPECT have found focal temporalhypoperfusion as the most common abnor-mality.3 14 While this was the case in our ownstudy, the proportion of patients (8/19) show-ing other patterns of rCBF abnormality wasnotably high. There was no obvious reason forthis; the population in the present study was ofsequentially selected patients with intractabledisease, similar to those of other studies,'1-7and there is no reason to suppose that HM-PAO SPECT is more likely to detect such

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CT, MR and SPECT imaging in temporal lobe epilepsy

abnormalities.4 Their detection is important, asbilateral abnormalities of rCBF must be regar-ded as representing at least a relative contrain-dication to surgery. A possible exception to thisis where an interictal scan shows hyperper-fusion contralateral to temporal hypoper-fusion. Three such cases appear in this series,and EEG, CT and MRI supported lateralisa-tion to the hypoperfused side. Two of thesepatients have been operated on and remainseizure free at nine months follow up.

Past studies have found that rCBF studies(PET or SPECT) detect lateralising abnor-malities in a higher proportion of patients thaneither CT or MRI,5 10o18 as was the case in ourstudy.The correlation between lateralisation based

on single surface EEG recording and that basedon hypoperfusion seen on PET or SPECT ispoor, but improves as the results of multiplerecordings are taken into account and becomesvery good when the results of all EEG inves-tigations, including depth electrodes etc, aretaken into account."8 Although the EEG inves-tigations of our patients were largely based onmultiple surface recordings, the correlationwith SPECT was excellent with only onedisagreement. In the one case where CT andMRI showed enlargement of one sylvian fis-sure and EEG lateralised to the other side,SPECT lateralisation agreed with EEG. Therewere otherwise no disagreements between scanresults and EEG. Complex partial seizureswith evidence of temporal lobe involvementmay originate in extratemporal areas. Amongthe many interictal PET and SPECT studies inthe literature there appear no patients withhypoperfusion confined to one temporal lobewho have seizures of extratemporal origin.Such PET and SPECT findings shouldtherefore be regarded as at least supportive of atemporal origin for seizures. Localisationwithin the temporal lobe is not currently possi-ble using interictal PET or SPECT.The results of this study show that low field

MRI is superior to modified CT in detectingabnormalities of the temporal lobe and suggestthat SPECT should become part of the stan-dard workup for temporal lobectomy. Thelatter investigation may prove a particularlypowerful lateralising tool when used to imagethe focal increases in blood flow seen at the siteofa focus during or just after a seizure.920 EEGis likely to remain the main lateralising inves-tigation in most patients, but the use of tech-niques such as MRI and SPECT may not onlyincrease the number of patients suitable forsurgery but, by improving patient selection,may improve outcome in terms of the propor-

tion of patients who benefit. In Glasgow we areembarking on a programme of temporal lobec-tomy with continuous audit of investigationsand results. We hope that this will identifythose techniques, whether imaging or electro-physiological, which are most effective inachieving a high success rate.

The SPECT scanner is funded by a grant fromthe Wellcome Trust to Professor J McCulloch,Wellcome Surgical Institute, University ofGlasgow and ProfessorM Brooks, DepartmentofPsychological Medicine, University of Glas-gow.

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10 Theodore WH, Dorwart R, Holmes M, Porter RJ, DiChiroG. Neuroimaging in refractory partial seizures. Compari-son of PET, CT and MRI. Neurology 1986;36:750-9.

11 Triulzi F, Francheschi M, Fazzio F, Del Maschio A.Nonrefractory temporal lobe epilepsy: 1 5 TMR imaging.Radiology 1988;166:181-5.

12 Kuzniecky R, DeLaSayette D, Ethier R, et al. Magneticresonance imaging in temporal lobe epilepsy: pathologicalcorrelations. Ann Neurol 1987;22:341-7.

13 Hougaard K, Oikawa T, Sveinsodittir E, Skinhoj E, IngvarDH, Lassen NA. Regional cerebral blood flow in focalcortical epilepsy. Arch Neurol 1976;33:527-35.

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