fifty - seven consecutive patients with pathologically - proven hippocampal sclerosis who underwent anterior temporal lobectomy between october 1994 and april 1997 for the treatment of intractable medial temporal lobe epilepsy and were followed - up for over 24 months were included in this study . thirty - eight were male and 19 were female , and their a mean age 33 ( range , 20 to 55 ) years . surgical candidates were determined on the basis of concordance among the various noninvasive examinations including clinical evaluation , scalp eeg , mr imaging , ictal video - eeg monitoring using scalp electrodes , neuropsychologic evaluation , interictal and ictal spect , and pet and/or the intracarotid amobarbital ( amytal ) test ( wada 's test ) . in a few selected patients with either ' normal ' mr imaging findings or discordance between mr imaging and pet and/or ictal spect , invasive intracranial subdural eeg study was performed . a pathologic diagnosis of hippocampal sclerosis was made qualitatively by an experienced neuropathologist without the aid of hippocampal neuronal counting . standard mr images were obtained using a 1.0 t or a 1.5 t unit , with conventional spin - echo t1-weighted sagittal and t2-weighted axial and coronal imaging procedures . in addition , 3-mm - thick t2-weighted fast spin - echo imaging and 1.5-mm - thick t1-weighted three - dimensional magnetization preparation rapid acquisition with gradient echo ( mprage ) imaging of the temporal lobes were performed in the oblique coronal plane . the angle of oblique coronal imaging was perpendicular to the long axis of the hippocampus , resulting in slight variation of angulation from patient to patient . spatial resolution was approximately 1.0 mm  1.0 mm ( matrix size 256  256 , fov 25 cm ) . all preoperative mr images were reviewed retrospectively by two neuroradiologists blinded to the postsurgical outcome . their visual interpretation focused on the presence or absence of hippocampal atrophy and increased t2 signal of the hippocampus . hippocampal atrophy was deemed to have occurred if one side of the hippocampus was asymmetrically small . this was best appreciated in oblique coronal images and characterized by a reduction in vertical and horizontal cross - sectional diameters . depending on whether one side of the hippocampus appeared smaller than the opposite side by 50% or more ( fig . equivocal findings of atrophy and of high t2 signal were resolved by consensus of the two neuroradiologists . at 24 months or more follow - up , postoperative outcome was classified by an epileptologist according to engel 's four categories ( 13 ) . class i ( seizure - free ) includes those who have been seizure - free since surgery ( or have experienced only auras , atypical generalized seizures occurring when antiepileptic medication is withdrawn ) , as well as those who enjoyed two years of seizure - free remission up to the most recent follow - up . class ii indicates rare seizures ; that is , a few seizures in a year . class iii denotes worthwhile improvement , meaning at least a 75% improvement in seizure frequency compared with preoperative status , while class iv indicates no worthwhile improvement . following analysis of the mr imaging findings and postsurgical outcome , individual mr imaging findings of hippocampal atrophy and high t2 hippocampal signal were correlated with postsurgical outcome . engel class i and ii were regarded as good outcome , and class iii and iv as poor outcome . fifty - seven consecutive patients with pathologically - proven hippocampal sclerosis who underwent anterior temporal lobectomy between october 1994 and april 1997 for the treatment of intractable medial temporal lobe epilepsy and were followed - up for over 24 months were included in this study . thirty - eight were male and 19 were female , and their a mean age 33 ( range , 20 to 55 ) years . surgical candidates were determined on the basis of concordance among the various noninvasive examinations including clinical evaluation , scalp eeg , mr imaging , ictal video - eeg monitoring using scalp electrodes , neuropsychologic evaluation , interictal and ictal spect , and pet and/or the intracarotid amobarbital ( amytal ) test ( wada 's test ) . in a few selected patients with either ' normal ' mr imaging findings or discordance between mr imaging and pet and/or ictal spect , invasive intracranial subdural eeg study was performed . a pathologic diagnosis of hippocampal sclerosis was made qualitatively by an experienced neuropathologist without the aid of hippocampal neuronal counting . standard mr images were obtained using a 1.0 t or a 1.5 t unit , with conventional spin - echo t1-weighted sagittal and t2-weighted axial and coronal imaging procedures . in addition , 3-mm - thick t2-weighted fast spin - echo imaging and 1.5-mm - thick t1-weighted three - dimensional magnetization preparation rapid acquisition with gradient echo ( mprage ) imaging of the temporal lobes were performed in the oblique coronal plane . the angle of oblique coronal imaging was perpendicular to the long axis of the hippocampus , resulting in slight variation of angulation from patient to patient . spatial resolution was approximately 1.0 mm  1.0 mm ( matrix size 256  256 , fov 25 cm ) . all preoperative mr images were reviewed retrospectively by two neuroradiologists blinded to the postsurgical outcome . their visual interpretation focused on the presence or absence of hippocampal atrophy and increased t2 signal of the hippocampus . hippocampal atrophy was deemed to have occurred if one side of the hippocampus was asymmetrically small . this was best appreciated in oblique coronal images and characterized by a reduction in vertical and horizontal cross - sectional diameters . depending on whether one side of the hippocampus appeared smaller than the opposite side by 50% or more ( fig . equivocal findings of atrophy and of high t2 signal were resolved by consensus of the two neuroradiologists . at 24 months or more follow - up , postoperative outcome was classified by an epileptologist according to engel 's four categories ( 13 ) . class i ( seizure - free ) includes those who have been seizure - free since surgery ( or have experienced only auras , atypical generalized seizures occurring when antiepileptic medication is withdrawn ) , as well as those who enjoyed two years of seizure - free remission up to the most recent follow - up . class ii indicates rare seizures ; that is , a few seizures in a year . class iii denotes worthwhile improvement , meaning at least a 75% improvement in seizure frequency compared with preoperative status , while class iv indicates no worthwhile improvement . following analysis of the mr imaging findings and postsurgical outcome , individual mr imaging findings of hippocampal atrophy and high t2 hippocampal signal were correlated with postsurgical outcome . engel class i and ii were regarded as good outcome , and class iii and iv as poor outcome . fisher 's exact test provided univariate analysis . good outcome was found in 93% of patients ( 53/57 ) ; 48 were engel class i and five were class ii . the remaining 7% ( 4/57 ) were in the poor outcome group ; three were class iii and one was class iv . hippocampal atrophy was seen in 96% of patients ( 55/57 ) , and was severe in 33 and mild in 22 . a high t2 hippocampal signal was detected in 61% of patients ( 35/57 ) , all of whom had combined atrophy . hippocampal atrophy only , without a high t2 signal , was noted in 35% ( 20/57 ) . no patient showed a high t2 signal only , nor did mr imaging reveal any case of bilateral hippocampal sclerosis . of 55 patients with hippocampal atrophy , 53 ( 96% ) had a good outcome , while only two ( 4% ) had a poor outcome . hippocampal atrophy was seen in 100% ( 48/48 ) ( fig . 1 ) and 100% ( 5/5 ) of patients in engel class i and ii groups , respectively , but in only 50% ( 2/4 ) of those with a poor outcome ( engel class iii and iv ) ( fig . the presence or absence of hippocampal atrophy showed significant correlation with surgical outcome ( p<0.01 ) . in the engel class i group , severe atrophy was seen in 58% of cases ( 28/48 ) and mild atrophy in 42% ( 20/48 ) . in the engel class ii group , all five patients showed severe atrophy , but this was observed in neither of the class iii patients ( fig . all the 33 patients with severe atrophy showed a good outcome ( engel class i and ii ) ; of the 22 with mild atrophy , 20 ( 91% ) showed a good outcome and only two ( 9% ) had a poor outcome . there was no significant difference in outcome between the severe and mild atrophy groups ( p>0.05 ) . the relationship between mr imaging findings of hippocampal atrophy and surgical outcome is set out in table 1 . of 35 patients with high t2 signal intensity , 33 ( 94% ) showed a good outcome and in only two ( 6% ) was the outcome poor . a high t2 signal was seen in 58% ( 28/48 ) and 100%(5/5 ) of engel class i and ii patients , respectively , but in 50% ( 2/4 ) of the poor outcome group ( engel class iii and iv ) . of 22 patients who showed no high t2 hippocampal signal , 20 ( 91% ) with only hippocampal atrophy had a good outcome ( engel class i ) , whereas two ( 9% ) with an apparently normal hippocampus had a poor outcome . the presence or absence of a high t2 signal did not significantly affect outcome ( p>0.05 ) . the relationship between a high t2 hippocampal signal , as revealed by mr imaging , and surgical outcome is seen in table 2 . of 55 patients with hippocampal atrophy , 53 ( 96% ) had a good outcome , while only two ( 4% ) had a poor outcome . . 1 ) and 100% ( 5/5 ) of patients in engel class i and ii groups , respectively , but in only 50% ( 2/4 ) of those with a poor outcome ( engel class iii and iv ) ( fig . the presence or absence of hippocampal atrophy showed significant correlation with surgical outcome ( p<0.01 ) . in the engel class i group , severe atrophy was seen in 58% of cases ( 28/48 ) and mild atrophy in 42% ( 20/48 ) . in the engel class ii group , all five patients showed severe atrophy , but this was observed in neither of the class iii patients ( fig . all the 33 patients with severe atrophy showed a good outcome ( engel class i and ii ) ; of the 22 with mild atrophy , 20 ( 91% ) showed a good outcome and only two ( 9% ) had a poor outcome . there was no significant difference in outcome between the severe and mild atrophy groups ( p>0.05 ) . the relationship between mr imaging findings of hippocampal atrophy and surgical outcome is set out in table 1 . of 35 patients with high t2 signal intensity , 33 ( 94% ) showed a good outcome and in only two ( 6% ) was the outcome poor . a high t2 signal was seen in 58% ( 28/48 ) and 100%(5/5 ) of engel class i and ii patients , respectively , but in 50% ( 2/4 ) of the poor outcome group ( engel class iii and iv ) . of 22 patients who showed no high t2 hippocampal signal , 20 ( 91% ) with only hippocampal atrophy had a good outcome ( engel class i ) , whereas two ( 9% ) with an apparently normal hippocampus had a poor outcome . the presence or absence of a high t2 signal did not significantly affect outcome ( p>0.05 ) . the relationship between a high t2 hippocampal signal , as revealed by mr imaging , and surgical outcome is seen in table 2 . in hippocampal sclerosis , atrophy of the hippocampus is the most common and consistent mr imaging finding . in such patients , significant correlation between hippocampal size , as determined by mr imaging , and hippocampal neuronal density has been observed ( 10 , 19 , 21 ) . in surgical specimens of 11 patients with cryptogenic temporal lobe epilepsy , bronen et al . ( 19 ) found a statistically significant correlation between hippocampal size , as measured by mr imaging , and neuronal density in ca3 and ca4 of the cornu ammonis and the granular cell layer of the hippocampus . our results indicated that in the preoperative evaluation of candidates for surgery among patients with hippocampal sclerosis , an mr imaging finding of hippocampal atrophy is the most useful sole prognostic indicator . although quantitative hippocampal volumetry has been shown to predict postsurgical outcome ( 4 ) , we demonstrated that the interpretation of mr images by visual inspection alone has a similar prognostic value . specifically , hippocampal atrophy , when apparent on visual inspection , independently predicted a good outcome . it has been suggested that a finding of hippocampal atrophy is more useful than one of high t2 signal ( 4 ) , and this is the case in the present study . indeed , we noted hippocampal atrophy more often than high t2 signal ( 97% vs. 61% ) , and 20 patients with hippocampal atrophy but no such signal showed a good outcome . the severity of atrophy did not , however , show significant correlation with surgical outcome , a finding which disagreed with the conclusions of jack et al . the reason for this disagreement is uncertain , but might be due to different evaluation methods : qualitative visual inspection in our study and quantitative volumetry in theirs . ( 4 ) reported a statistically significant correlation between computer - assisted measurement of hippocampal volume ( atrophy ) and surgical outcome ( i.e. postoperative seizure control ) in 50 patients . in their study , 34 ( 97% ) of 35 patients in whom hippocampal atrophy and eeg concordantly lateralized the focus of seizure had a satisfactory outcome , whereas in eight ( 53% ) of the remaining 15 with either no hippocampal atrophy or hippocampal atrophy discordant with eeg , the outcome was satisfactory . in their prospective study using visual interpretation , kuzniecky et al . ( 17 ) reported that as indicators of surgical success , abnormal mr images had an 82% predictive value and normal images had a 56% predictive value . they suggested that the best predictor of favorable surgical outcome was hippocampal atrophy ( p<0.09 ) . increased hippocampal t2 signal , reflecting gliosis , is another important indicator of hippocampal sclerosis ( 7 , 9 , 22 ) . the degree and extent of hippocampal gliosis also correlate with the t2 signal in the hippocampus ( 22 , 23 ) . ( 22 ) found a high signal in 71% of patients with severe gliosis and in 50% of those with moderate gliosis . they stated that in most cases the severity of pathologic change corresponded to the intensity of the abnormal signals seen on t2-weighted images . in some cases , however , no agreement was found , and the location of the abnormal signal intensity did not always correlate with the distribution of observed histologic change ( 22 ) . previous mr imaging studies have described a variable frequency of t2 signal change in the hippocampus : change was observed in 12% to 65% of patients with hippocampal sclerosis ( 6 , 8 , 19 ) . in the present study , the increased signal observed on t2-weighted images occurred in 61% of cases . because it detected the high signal intensity of hippocampal sclerosis more frequently than did the usual t2-weighted sequence , jack et al . ( 24 ) recommended the routine use of the fluid - attenuated inversion recovery ( flair ) pulse sequence in patients with temporal lobe epilepsy . if the flair sequence had been used in this study , a high hippocampal signal would probably have been detected in more patients ; at the time of the study the sequence was not available however . garcia et al . ( 18 ) reported that in a prospective study involving visual inspection , both ipsilateral hippocampal atrophy and increased ipsilateral hippocampal signal independently predicted a seizure - free outcome . in the present study , however , for reasons which are uncertain , high t2 signal intensity did not significantly correlate with surgical outcome ( p>0.05 ) . in this study , the causes of poor outcome seen in four patients are not known ; in two patients whose mr imaging findings appeared normal , pet , ictal eeg and the findings of invasive intracranial eeg suggested a lateralizing focus and led to surgery . in the other two patients , mr imaging findings of mild atrophy and a high t2 hippocampal signal were concordant with the findings of pet and/or ictal eeg . the poor outcome in these cases might be because postsurgical scierotic tissue remnants were more widespred . in conclusion , of the two primary mr imaging findings of hippocampal sclerosis , hippocampal atrophy is more common and shows closer correlation with surgical outcome than does a high t2 signal . it therefore appears to be the more useful predictor of surgical outcome in patients with hippocampal sclerosis , though the reason for the strong correlation between hippocampal atrophy and outcome is not certain .