Summary: A new study highlights the potential reasons why many patients with severe epilepsy still continue to experience seizures even after surgery.
Source: University of Liverpool.
New research from the University of Liverpool, published in the journal Brain, has highlighted the potential reasons why many patients with severe epilepsy still continue to experience seizures even after surgery.
Epilepsy continues to be a serious health problem and is the most common serious neurological disorder. Medically intractable temporal lobe epilepsy (TLE) remains the most frequent neurosurgically treated epilepsy disorder.
Many people with this condition will undergo a temporal lobe resection which is a surgery performed on the brain to control seizures. In this procedure, brain tissue in the temporal lobe is resected, or cut away, to remove the seizure focus.
Unfortunately, approximately one in every two patients with TLE will not be rendered completely seizure free after temporal lobe surgery, and the reasons underlying persistent postoperative seizures have not been resolved.
Understanding the reasons why so many patients continue to experience postoperative seizures, and identifying reliable biomarkers to predict who will continue to experience seizures, are crucial clinical and scientific research endeavours.
Researchers from the University’s Institute of Translational Medicine, led by Neuroimaging Lead Dr Simon Keller and collaborating with Medical University Bonn (Germany), Medical University of South Carolina (USA) and King’s College London, performed a comprehensive diffusion tensor imaging (DTI) study in patients with TLE who were scanned preoperatively, postoperatively and assessed for postoperative seizure outcome.
Diffusion tensor imaging (DTI) is a MRI-based neuroimaging technique that provides insights into brain network connectivity.
The results of these scans allowed the researchers to examine regional tissue characteristics along the length of temporal lobe white matter tract bundles. White matter is mainly composed of axons of nerve cells, which form connections between various grey matter areas of the brain, and carry nerve impulses between neurons allowing communication between different brain regions.
Through their analysis the researchers could determine how abnormal the white matter tracts were before surgery and how the extent of resection had affected each tract from the postoperative MRI scans.
The researchers identified preoperative abnormalities of two temporal lobe white matter tracts that are not included in standardised temporal lobe surgery in patients who had postoperative seizures but not in patients with no seizures after surgery.
The two tracts were in the ‘fornix’ area on the same side as surgery, and in the white matter of the ‘parahippocampal’ region on the opposite side of the brain.
The tissue characteristics of these white matter tracts enabled researchers to correctly identify those likely to have further seizures in 84% of cases (sensitivity) and those unlikely to have further seizures in 89% of cases (specificity). This is significantly greater than current estimates.
The researchers also found that a particular temporal lobe white matter tract called the ‘uncinate fasciculus’ was abnormal – and potentially involved in the generation of seizures – in patients with excellent and suboptimal postoperative outcomes.
However, it was found that significantly more of this tract was surgically resected/removed in the patients with an excellent outcome.
Dr Simon Keller, said: “There is scarce information on the prediction of postoperative seizure outcome using preoperative imaging technology, and this study is the first to rigorously investigate the tissue characteristics of temporal lobe white matter tracts with respect to future seizure classifications.
“Although there is some way to go before this kind of data can influence routine clinical practice, these results may have the potential to be developed into imaging prognostic markers of postoperative outcome and provide new insights for why some patients with temporal lobe epilepsy continue to experience postoperative seizures.”
About this neurology research article
Source: Simon Wood – University of Liverpool Image Source: NeuroscienceNews.com image is credited to Keller et al./Brain. Original Research: Full open access research for “Preoperative automated fibre quantification predicts postoperative seizure outcome in temporal lobe epilepsy” by Simon S. Keller, G. Russell Glenn, Bernd Weber, Barbara A. K. Kreilkamp, Jens H. Jensen, Joseph A. Helpern, Jan Wagner, Gareth J. Barker, Mark P. Richardson, Leonardo Bonilha in Brain. Published online November 15 2016 doi:10.1093/brain/aww280
Cite This NeuroscienceNews.com Article
[cbtabs][cbtab title=”MLA”]University of Liverpool. “Epilepsy: Why Do Seizures Sometimes Continue After Surgery?.” NeuroscienceNews. NeuroscienceNews, 17 November 2016. <https://neurosciencenews.com/epilepsy-seizures-surgery-5552/>.[/cbtab][cbtab title=”APA”]University of Liverpool. (2016, November 17). Epilepsy: Why Do Seizures Sometimes Continue After Surgery?. NeuroscienceNews. Retrieved November 17, 2016 from https://neurosciencenews.com/epilepsy-seizures-surgery-5552/[/cbtab][cbtab title=”Chicago”]University of Liverpool. “Epilepsy: Why Do Seizures Sometimes Continue After Surgery?.” https://neurosciencenews.com/epilepsy-seizures-surgery-5552/ (accessed November 17, 2016).[/cbtab][/cbtabs]
Approximately one in every two patients with pharmacoresistant temporal lobe epilepsy will not be rendered completely seizure-free after temporal lobe surgery. The reasons for this are unknown and are likely to be multifactorial. Quantitative volumetric magnetic resonance imaging techniques have provided limited insight into the causes of persistent postoperative seizures in patients with temporal lobe epilepsy. The relationship between postoperative outcome and preoperative pathology of white matter tracts, which constitute crucial components of epileptogenic networks, is unknown. We investigated regional tissue characteristics of preoperative temporal lobe white matter tracts known to be important in the generation and propagation of temporal lobe seizures in temporal lobe epilepsy, using diffusion tensor imaging and automated fibre quantification. We studied 43 patients with mesial temporal lobe epilepsy associated with hippocampal sclerosis and 44 healthy controls. Patients underwent preoperative imaging, amygdalohippocampectomy and postoperative assessment using the International League Against Epilepsy seizure outcome scale. From preoperative imaging, the fimbria-fornix, parahippocampal white matter bundle and uncinate fasciculus were reconstructed, and scalar diffusion metrics were calculated along the length of each tract. Altogether, 51.2% of patients were rendered completely seizure-free and 48.8% continued to experience postoperative seizure symptoms. Relative to controls, both patient groups exhibited strong and significant diffusion abnormalities along the length of the uncinate bilaterally, the ipsilateral parahippocampal white matter bundle, and the ipsilateral fimbria-fornix in regions located within the medial temporal lobe. However, only patients with persistent postoperative seizures showed evidence of significant pathology of tract sections located in the ipsilateral dorsal fornix and in the contralateral parahippocampal white matter bundle. Using receiver operating characteristic curves, diffusion characteristics of these regions could classify individual patients according to outcome with 84% sensitivity and 89% specificity. Pathological changes in the dorsal fornix were beyond the margins of resection, and contralateral parahippocampal changes may suggest a bitemporal disorder in some patients. Furthermore, diffusion characteristics of the ipsilateral uncinate could classify patients from controls with a sensitivity of 98%; importantly, by co-registering the preoperative fibre maps to postoperative surgical lacuna maps, we observed that the extent of uncinate resection was significantly greater in patients who were rendered seizure-free, suggesting that a smaller resection of the uncinate may represent insufficient disconnection of an anterior temporal epileptogenic network. These results may have the potential to be developed into imaging prognostic markers of postoperative outcome and provide new insights for why some patients with temporal lobe epilepsy continue to experience postoperative seizures.
“Preoperative automated fibre quantification predicts postoperative seizure outcome in temporal lobe epilepsy” by Simon S. Keller, G. Russell Glenn, Bernd Weber, Barbara A. K. Kreilkamp, Jens H. Jensen, Joseph A. Helpern, Jan Wagner, Gareth J. Barker, Mark P. Richardson, Leonardo Bonilha in Brain. Published online November 15 2016 doi:10.1093/brain/aww280