'MRI-negative PET-positive' temporal lobe epilepsy (TLE) and mesial TLE differ with quantitative MRI and PET: a case control study
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Network Analysis of the Default Mode Network Using Functional Connectivity MRI in Temporal Lobe Epilepsy
Published on: August 5, 2014
Ross P Carne1, Terence J O'Brien, Christine J Kilpatrick
1Victorian Epilepsy Centre, St Vincent's Hospital, Melbourne, Australia. carnero@svhm.org.au
Background:
'MRI negative PET positive temporal lobe epilepsy' represents a substantial minority of temporal lobe epilepsy (TLE). Clinicopathological and qualitative imaging differences from mesial temporal lobe epilepsy are reported. We aimed to compare TLE with hippocampal sclerosis (HS+ve) and non lesional TLE without HS (HS-ve) on MRI, with respect to quantitative FDG-PET and MRI measures.
Methods:
30 consecutive HS-ve patients with well-lateralised EEG were compared with 30 age- and sex-matched HS+ve patients with well-lateralised EEG. Cerebral, cortical lobar and hippocampal volumetric and co-registered FDG-PET metabolic analyses were performed.
Results:
There was no difference in whole brain, cerebral or cerebral cortical volumes. Both groups showed marginally smaller cerebral volumes ipsilateral to epileptogenic side (HS-ve 0.99, p = 0.02, HS+ve 0.98, p < 0.001). In HS+ve, the ratio of epileptogenic cerebrum to whole brain volume was less (p = 0.02); the ratio of epileptogenic cerebral cortex to whole brain in the HS+ve group approached significance (p = 0.06). Relative volume deficits were seen in HS+ve in insular and temporal lobes. Both groups showed marked ipsilateral hypometabolism (p < 0.001), most marked in temporal cortex. Mean hypointensity was more marked in epileptogenic-to-contralateral hippocampus in HS+ve (ratio: 0.86 vs 0.95, p < 0.001). The mean FDG-PET ratio of ipsilateral to contralateral cerebral cortex however was low in both groups (ratio: HS-ve 0.97, p < 0.0001; HS+ve 0.98, p = 0.003), and more marked in HS-ve across all lobes except insula.
Conclusion:
Overall, HS+ve patients showed more hippocampal, but also marginally more ipsilateral cerebral and cerebrocortical atrophy, greater ipsilateral hippocampal hypometabolism but similar ipsilateral cerebral cortical hypometabolism, confirming structural and functional differences between these groups.
Insights
MRI-negative PET-positive temporal lobe epilepsy (TLE) shows distinct structural and functional differences compared to TLE with hippocampal sclerosis. Quantitative imaging reveals subtle atrophy and hypometabolism patterns unique to each group.
Area of Science:
- Neurology
- Radiology
- Epilepsy Research
Background:
- A significant subset of temporal lobe epilepsy (TLE) is characterized as 'MRI negative PET positive'.
- These patients exhibit clinicopathological and qualitative imaging distinctions from mesial temporal lobe epilepsy.
- This study investigates quantitative imaging differences between TLE with hippocampal sclerosis (HS+ve) and non-lesional TLE without hippocampal sclerosis (HS-ve).
Purpose of the Study:
- To quantitatively compare MRI and FDG-PET measures in HS+ve TLE versus HS-ve TLE.
- To identify structural and functional imaging biomarkers differentiating these TLE subtypes.
Main Methods:
- Comparison of 30 HS-ve patients with 30 age- and sex-matched HS+ve patients, all with well-lateralized EEG.
- Performance of cerebral, cortical lobar, and hippocampal volumetric analyses.
- Execution of co-registered FDG-PET metabolic analyses.
Main Results:
- No significant differences in whole brain, cerebral, or cerebral cortical volumes were observed between groups.
- Both groups exhibited marginally smaller ipsilateral cerebral volumes relative to the epileptogenic side.
- HS+ve patients displayed greater relative volume deficits in the insular and temporal lobes, and more marked hippocampal hypometabolism.
- Both groups showed significant ipsilateral cerebral cortical hypometabolism, which was more pronounced in HS-ve patients across most lobes.
Conclusions:
- HS+ve patients demonstrated more pronounced hippocampal atrophy and greater ipsilateral hippocampal hypometabolism.
- Marginal ipsilateral cerebral and cerebrocortical atrophy was noted in HS+ve patients.
- Similar patterns of ipsilateral cerebral cortical hypometabolism were observed in both groups, confirming distinct structural and functional characteristics between HS+ve and HS-ve TLE.