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Determination of individual language dominance is a crucial issue in the presurgical evaluation of patients with focal epilepsy syndromes to spare cortical language areas during resective neurosurgery. In patients with lesions within the left frontal or temporal lobe higher rates of atypical (not left hemispheric) language dominance have been demonstrated. Atypical language dominance can be accompanied by other functional reorganisation processes such as atypical memory dominance, which can be advantageous for postoperative cognitive outcome after resections within the left hemisphere.
The work presented here evaluated two methods for the individual assessment of language dominance, the Wada-Test, an invasive method and the “gold standard” in presurgical evaluation of epilepsy patients, and functional transcranial Dopplersonography (fTCD) as a potential non-invasive alternative.
A survey study at 23 epilepsy centers showed that the Wada-Test albeit methodological criticism and growing availability of non-invasive functional imaging methods, is still frequently but more restrictively (e.g. not in all surgical candidates) used than reported in former studies. However, clinicians at present do not want to solely rely on the results of non-invasive imaging techniques.
Resembling the results of former studies, a study that compared the results of fTCD and the Wada-Test showed high concordance between the two methods in candidates for epilepsy surgery. A case report showed further evidence that fTCD is also able to reliably detect atypical language dominance. Unlike the Wada-Test and fMRI, fTCD often can be used in children and mentally disabled persons.
Since fTCD can be repeatedly conducted and can also be applied without clinical indications (e.g. in healthy volunteers) it can be used for scientific research. In one study language dominance in TLE patients and healthy controls were compared and a higher rate of atypical language dominance could be shown for the TLE patients.
In summary, fTCD probably will be able to replace the Wada-Test in a substantial proportion of surgical candidates.