Abstracts

Mesial temporal lobe structures (MTLS) of temporal lobe epilepsy (TLE) patients are frequently smaller on the side of the epileptogenic zone. We investigated whether volumetric differences involve all segments of the MTLS in pharmacoresistant TLE patients. In a subset of patients undergoing bilateral depth electrode evaluation, we also determined whether ictal onset corresponds to segmental atrophy., 29 patients who had undergone temporal lobectomy for non-lesional pharmacoresistant TLE and 18 controls were studied. 8 patients had bitemporal depth evaluations prior to surgery. Using in-house developed software, we measured MTLS volumes and corrected for hemispheric size on high-resolution T1-weighted scans (values given in cm³). Hippocampal head, body and tail were defined as the segments along the anterior, middle and posterior third in anterior-posterior direction on the coronal scan. Segmental atrophy was defined as volumetric asymmetry greater than 2 standard deviations compared to asymmetry in the control group. In the 8 patients who had undergone bilateral depths electrode monitoring prior to temporal lobectomy, EEG seizure onsets were analyzed and mapped to individual hippocampal segments. Pathology of all patients was reviewed and correlated with imaging findings., 28 patients had a favorable outcome at six months (Engel class 1 or 2); one outcome is pending. 17 out of 29 patients had atrophy of the hippocampus ipsilateral to the epileptogenic zone. Segmental atrophy occurred more frequently in the tail (n = 16) and body (n = 15) than the head (n = 5).
Overall, resected hippocampi (n = 29) were 13% smaller compared to contralateral hippocampi and 10% smaller compared to ipsilateral hippocampi in control subjects (Resected side: MTLS 3.45[plusmn]0.69, Contralateral side MTLS 3.95[plusmn]0.67, p [lt] 0.0001; Control MTLS 3.84[plusmn]0.78, p = 0.01). Segmental differences between patients and controls were obvious in the hippocampal tail (23% compared to contralateral side in patients, p [lt] 0.0001; 21% compared to the ipsilateral side of the control group, p = 0.003) and body (19%, p = 0.0001 and 19%, p = 0.0004), but less obvious in the hippocampal head (6%, p = 0.02; and 1% (not significant).
Out of 68 seizures analyzed in 8 patients with invasive monitoring, 26 arose from the hippocampal head, 20 from the hippocampal body and 15 from the hippocampal tail. Ictal onsets occurred in 25% of atrophic segments and 65% of non-atrophic segments. 7 seizures (10%) had extrahippocampal onset., Hippocampal bodies and tails but not heads are relatively atrophic in patients with pharmacoresistant TLE. Ictal onset does not correlate with segmental atrophy in the mesial temporal lobe structures.,