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Investigations on Alterations of Hippocampal Circuit Function Following Mild Traumatic Brain Injury
Published on: November 19, 2012
Hippocampal pathology in refractory temporal lobe epilepsy: T2-weighted signal change reflects dentate gliosis
Regula S Briellmann1, Renate M Kalnins, Samuel F Berkovic
1Brain Research Institute, Department of Neurology, Austin and Repatriation Medical Center, Heidleberg West, Victoria, Australia.
Background:
The MR and pathologic features of hippocampal sclerosis (HS) are well described and include volume decrease and T2-weighted signal increase for MRI, and neuron cell loss and gliosis for pathology.
Objective:
To confirm the established correlation between hippocampal volumes and neuron cell counts, and to study the still controversial association between signal change and gliosis.
Methods:
The authors studied 44 patients (22 men and 22 women; mean age at surgery, 37 years) with refractory temporal lobe epilepsy. Quantitative assessment of hippocampal volumes and T2 relaxometry, and neuron and glial cell count in the region CA1 and molecular layer of the dentate gyrus was performed. The proportion of glial fibrillary acidic protein (GFAP)-positive glial cells (reactive astrocytes) was indicated.
Results:
In a stepwise regression, the ipsilateral hippocampal volume was predicted best by the neuron cell count in the dentate gyrus (p = 0.005, r = 0.4). Hippocampal T2 time, however, was predicted best by the glial cell count in the dentate gyrus (p = 0.01, r = 0.4). None of the other cell counts contributed to either model. In the dentate, 31% of the glial cells were reactive astrocytes, whereas in CA1, 5% were reactive.
Conclusion:
The results confirmed the correlation between hippocampal volumes and neuron cell counts. T2-weighted signal increase in the hippocampus was mainly influenced by gliosis in the dentate gyrus, where a high proportion of glial cells show abnormal activity. This activity may reflect changes important in the development of hippocampal epileptogenicity.
Insights
Hippocampal volume correlates with neuron loss in epilepsy. Increased MRI signal intensity is linked to glial cell activity in the dentate gyrus, suggesting a role in epileptogenicity.
Area of Science:
- Neuroscience
- Neuropathology
- Medical Imaging
Background:
- Hippocampal sclerosis (HS) presents with characteristic MRI findings like reduced volume and increased T2-weighted signal.
- Pathologically, HS involves neuron loss and gliosis within the hippocampus.
Purpose of the Study:
- To validate the relationship between hippocampal volume and neuron counts.
- To investigate the association between MRI signal changes and gliosis in HS.
Main Methods:
- Quantitative MRI (volumes, T2 relaxometry) and cell counting (neurons, glial cells, reactive astrocytes) were performed on 44 epilepsy patients.
- Specific regions analyzed included CA1 and the dentate gyrus.
Main Results:
- Ipsilateral hippocampal volume was significantly predicted by neuron cell count in the dentate gyrus (p=0.005).
- Hippocampal T2 time was best predicted by glial cell count in the dentate gyrus (p=0.01).
- The dentate gyrus showed 31% reactive astrocytes, compared to 5% in CA1.
Conclusions:
- The study confirms the correlation between hippocampal volume and neuron cell counts.
- Increased hippocampal T2 signal is primarily influenced by gliosis in the dentate gyrus.
- Active gliosis in the dentate gyrus may contribute to hippocampal epileptogenicity.
