Abstracts

To determine seizure propagation patterns in patients undergoing assessment for refractory partial epilepsy, A dataset of ^99mTc-HMPAO SPECT studies in patients (median age 29) who had undergone focal epilepsy surgery resections (Engel I [amp] II) at Westmead Hospital yielded 20 frontal lobe epilepsy (FLE), 33 mesial temporal lobe epilepsy (MTLE) and 8 parieto-occipital lobe epilepsy (POLE). Using ictal-interictal SPECT analyzed by Statistical Parametric Mapping, perfusion changes were determined ¹. The subtracted images were mapped onto Tzourio-Mazoyer[apos]s Brain Map and the significance of hyperperfusion and hypoperfusion was extracted for each region of interest ². SPECT injection times were normalised to seizure duration (injection time/seizure duration) to examine ictal and postictal perfusion changes using data from a population of patients injected at different points in their seizures, MTLE showed marked hyperperfusion in the ipsilateral mesial regions and temporal neocortex which persisted into early postictal phase. Contralateral temporal neocortex hyperperfusion occurred in the early ictal phase. FLE showed immediate intense hyperperfusion in ipsilateral frontal lobe. The contralateral frontal regions and bilateral temporal regions also showed early ictal involvement in FLE. As the seizure progresses into mid-ictal period, ipsilateral frontal perfusion became indistinguishable from the other parts of the brain and in late ictal phase hyperperfusion predominated in ipsilateral and contralateral parieto-occipital regions. POLE showed early ictal hyperperfusion in the ipsilateral parietal region with early involvement of the ipsilateral frontal region and a later involvement of the ipsilateral temporal region and basal ganglia. Regional hypoperfusion was not confined to the postictal phase but was seen remote to the lobe of onset in the ictal phase in MTLE, FLE and POLE. Ictal hypoperfusion was most marked in FLE occurring in the parieto-occipital region bilaterally., In MTLE, seizure activity showed minimal extratemporal spread. In FLE, the changes suggested rapid seizure propagation from ipsilateral frontal region to the bilateral frontal and temporal lobes. In POLE, the seizures project anteriorly initially to ipsilateral frontal lobe and later the temporal region. These results highlight the importance of early ictal isotope injection in extratemporal lobe epilepsies. Ictal SPECT perfusion patterns can give insights into partial seizure propagation patterns beyond the lobe of seizure onset.
Reference:
1. McNally KA et al, Localizing value of intal-interectal SPECT anlysed by SPM, Epilepsia 2005, 46: 1450-64
2. Tzourio-Mazoyer N et al, Automated anatomical labeling of activation in SPM using a macroscopic parcellation of the MNI MRI single-subject brain, Neuroimage 2002, 15: 273-89., (Supported by Australian Postgraduate Award.)