The noninvasive localisation of brain abnormality in intractable focal epilepsy in childhood

The work described in this thesis evaluates the role of noninvasive magnetic resonance and nuclear medicine techniques in the investigation of focal epilepsy of childhood, and more specifically in the presurgical evaluation of children who are potential candidates for surgery. Seventy five children were prospectively investigated after referral for assessment and investigation of intractable focal epilepsy. Initial clinical localisation was made on the basis of full clinical assessment with EEG. All underwent magnetic resonance imaging. Abnormalities were found in 88% of children, concordant with the seizure focus in 80%. Further magnetic resonance techniques were assessed with regard to lateralisation of temporal lobe epilepsy (TLE). T2 relaxometry of the hippocampi and proton magnetic resonance spectroscopy (1H MRS) of the mesial temporal lobes were demonstrated to be lateralising in a high proportion of these children, and also showed a high rate of bilateral abnormality. In order to relate these structural abnormalities to the epileptogenic focus, the technique of ictal single photon emission computed tomography (SPECT), using 99Tcm HMPAO as a marker of cerebral blood flow, was developed for this study. Focal hyperperfusion was seen in 72% of ictal scans when compared to interictal scans, concordant with the seizure focus in all. Where no perfusion change was noted after an ictal injection, slowing of the EEG was present at the time of injection consistent with ischaemia, suggesting rCBF does not increase in all focal seizures. Correlation of interictal SPECT scans with 1H MRS of the mesial temporal regions in children with TLE demonstrated correlation between neuronal loss or dysfunction and hypoperfusion. Where similar damage on the two sides was demonstrated by 1H MRS, no asymmetry of interictal perfusion was seen. These findings have led to a better understanding of the underlying pathophysiology of intractable focal epilepsy of childhood and have resulted in an increase in the number of children evaluated for epilepsy surgery. The thesis concludes with a discussion of an optimised noninvasive strategy for presurgical evaluation in children