LTLE was defined as an epilepsy syndrome fulfilling three criteria: (1) a discrete lesion or ictal onset zone confirmed by invasive study, located exclusively outside the collateral sulcus, (2) absence of hippocampal atrophy or signal changes under magnetic resonance imaging (MRI) when employing 3-mm sections perpendicular to the long axis of the hippocampus, and (3) achievement of good postsurgical outcome (Engel class I or II) for at least one year.7 LTLE was categorized into anterior or posterior LTLE (ALTLE or PLTLE) according to whether the location of the epileptogenic zone was anterior or posterior to the line across the cerebral peduncle (Fig. 1). Patients with a large lesion covering both the anterior and posterior temporal lobes were excluded. 13 patients fulfilled our criteria of ALTLE, and 8 fulfilled the criteria of PLTLE, out of 92 consecutive patients who were operated upon for LTLE between 1994 and 2001 (Table 1). All patients became seizure-free after the operation except for 2 PLTLE patients who experienced very occasional seizures (Engel Class II). MTLE was defined when hippocampal sclerosis was detected on MRI in the absence of other structural lesions, and the patient had been seizure free for at least one year after standard anterior temporal lobectomy with amygdalohippocampectomy. Over the same period, 21 patients that were randomly selected from 204 MTLE patients fulfilled the criteria.

All patients received presurgical evaluations including video-EEG monitoring, MRI, Fluoro-deoxyglucose (FDG) PET, ictal SPECT if possible, and Wada test. 4 ALTLE patients, 6 PLTLE patients, and 1 MTLE patient undertook intracranial EEG recording. 6 ALTLE patients, 5 with PLTLE, and 14 with MTLE received ictal SPECT. 9 ALTLE patients received an anterior temporal lobectomy with amygdalohippocampectomy and four ALTLE patients received anterior temporal neocortical resection only. 5 PLTLE patients recieved lesionectomy, 3 PLTLE patients received additional anterior temporal lobectomy with amygdalohippocampectomy because of rapid propagation of ictal rhythm to the anterior temporal areas. The MTLE patients received anterior temporal lobectomy to a variable extent (3.5~5 cm) depending on the side of epileptogenic lobe and amygdalohippocampectomy. Gross and microscopic tissue analyses were performed in all cases.

Demographic data, age at onset of afebrile seizure, frequency of seizure, auras, and outcomes were retrospectively reviewed from medical records. Auras were classified as epigastric, psychic, memory-related, auditory, vertigo, visual, or other. Epigastric aura included epigastric uprising sense, nausea, vomiting, and discomfort in the epigastric area. Psychic aura included anxiety, fear, forced thinking, and a feeling of unreality. Memory-associated aura included déjà vu, strange feelings, flashback, and panoramic experience. Auditory aura included tinnitus, deafness, and hallucination.

All patients were monitored using continuous video-EEG monitoring using scalp electrodes according to the international 10/20 system, and with additional anterior temporal electrodes (T1 and T2). Antiepileptic medications were discontinued during the monitoring. Total 107 seizures (34 seizures in 13 ALTLE patients, 19 in 8 PLTLE patients, and 54 in 21 MTLE patients) were analyzed. Ictal onset was defined by earlier sign of symptom and EEG. Ictal onset by symptom was defined as the time when a patient first experienced an aura, or when altered responsiveness or abnormal movement was first noticed. Ictal onset based on EEG was defined as the onset of rhythmic activity. The end of a seizure was defined as the end of the ictal EEG rhythm. Initial symptoms, ictal behaviors, duration of complex partial seizure, and latency to the onset of generalized tonicclonic seizure (GTCS) were analyzed. We classified ictal behaviors as follows: oroalimentary automatism, hand automatism, dystonia of the upper extremity, staring or behavioral arrest, looking around, body shifting, hyperactivity, version, facial twitching, limb clonic movement, and limb tonic movement. Dystonia and tonic movement were differentiated by a twisting component. Version was defined as a forced turning of the head or eyeball. Ictal EEGs were reviewed by one of the authors (S.K.L.) blinded to patient information, including semiology and resection site. A total of 110 ictal EEGs of adequate quality (30, 22, and 58 EEG recordings of the 13 ALTLE, 8 PLTLE, and 21 MTLE patients, respectively) were analyzed. Ictal EEGs were analyzed with respect to location and rhythm. The ictal pattern distributions were classified as follows8:

Focal and regional patterns originating from temporal electrodes were subdivided into anterior temporal and posterior temporal onset. Ictal onset from T1 and T3 electrodes (or T2, T4) was classified as anterior temporal regional onset pattern, whereas ictal onset from T5 and T3 (or T6, T4) electrodes was classified as posterior temporal regional onset pattern. F7, T1, and T3 (or F8, T2, and T4) ictal onset was classified as anterior temporal regional onset pattern (not lobar).

All initial ictal rhythms were also classified on the frequency spectrum.

We used χ² analysis and Fisher's exact test for categorical variables to evaluate the significance of differences in the occurrence of features between the groups. Duration of seizure and age were compared using ANOVA or the Kruskal-Wallis test for continuous variables. Statistical significance was accepted when P< 0.05.

The demographic data are summarized in Table 2. Age, sex, side of lesion, onset age of afebrile seizure, and seizure frequency did not differ significantly between the groups.

Epigastric aura was less common in PLTLE and ALTLE than MTLE, but not significantly (P=0.161, Fisher's exact test). Psychic auras were absent in PLTLE. Memory-associated aura did not differentiate the site of lesion. Visual and vertiginous auras were reported in PLTLE, and auditory auras were reported in both ALTLE and PLTLE. Some patients had more than one type of aura (Table 3).

Initial oroalimentary automatism was not observed in PLTLE, which distinguished it from ALTLE and MTLE. Initial hypomotor symptoms such as staring and behavioral arrest were more frequent in PLTLE (P<0.001, χ² analysis). Initial hypermotor activity was observed in only one ALTLE patient. Version and GTCS occurred more frequently in ALTLE and PLTLE than in MTLE (version: P=0.005, χ² analysis; GTCS: P=0.001, χ² analysis). Looking around was more frequent in MTLE than in ALTLE and PLTLE (P=0.004, Fisher's exact test). No differences were observed in the occurrences of oroalimentary automatism, hand automatism, hypermotor activity, body shifting, dystonia, facial twitching, limb clonus, or tonic posturing (Table 4). Secondary GTCS (Table 5) occurred significantly earlier in PLTLE than in ALTLE or MLTLE (P<0.001, Kruskal-Wallis test).

Focal or regional EEG ictal onset was observed in 43%, 59%, and 28% of ALTLE, PLTLE, and MTLE patients, respectively. The most common ALTLE pattern was anterior temporal regional onset (11 of 30 seizures). However, 2 ALTLE seizures originated from the posterior temporal electrodes, and 7 were falsely localized to the contralateral temporal (5 seizures) or the ipsilateral frontal lobe (2 seizures). The most common pattern of PLTLE was posterior temporal onset (7 of 22 seizures). There were 5 PLTLE seizures that originated from the anterior temporal electrodes, and 2 were falsely localized to the ipsilateral frontal lobe. MTLE had rather diffuse ictal onset. There were 11, 15, and 11 seizures of the lobar, hemispheric, and bilateral patterns, respectively. Ictal onset was confined to the anterior temporal electrodes in 15 MTLE seizures and confined to the posterior temporal electrodes in 1 MTLE seizure (Table 6).

In all types, the most common initial ictal rhythm was rhythmic theta. Fast activities of the alpha or beta range were more common in PLTLE and ALTLE than in MTLE (P=0.002, χ² analysis); beta activity was not observed in MTLE (Table 6).