Abstracts

We compare composite SISCOM patterns between right and left medial temporal onset complex partial seizures to investigate possible perfusion pattern differences. Such differences may explain why right temporal seizures, in comparison to left temporal seizures, cause a lesser degree of loss of consciousness. We retrospectively reviewed and selected, consecutively, 32 subjects who had confirmed medial TLE and underwent ictal SPECT. Using video-EEG recordings, we recorded the time sequence of all seizure semiology, including a rating of patients[apos] behavior during seizures using a simple two level classification to determine impairment of consciousness. The SPECT images from subjects with ictal impairment of consciousness were then classified into right and left TLE groups. Using a previously described technique, composite SISCOM images were produced for each group. We then compared the statistical maps of perfusion changes in each group, examining both hyperperfusion and hypoperfusion changes. Thirty-one patients (15 right-sided and 16 left-sided) had TLE of medial temporal onset with associated impairment of consciousness. The mean age, ictal injection time, and seizure duration for the right-sided group was 40.1 years, 32 s, 93 s, and for the left-sided group was 32.5 years, 31 s, 91 s, respectively. The ictal SPECT injection occurred during motionless staring in 5 subjects (3 right and 2 left), automatism in 14 subjects (7 right and 7 left), dystonic posturing in 7 subjects (3 right and 4 left), and versive head movements in 5 subjects (2 right and 3 left). Composite SISCOM images showed similar regions of hyperperfusion change in the ipsilateral temporal lobe, basal ganglia, and insula in both groups. In the region of the brainstem tegmentum there was a 1 standard deviation or greater hyperperfusion change in 2 of 15 subjects (P=0.56) in the right TLE group, and 7 of 16 subjects (P=0.008) in the left TLE group. Visual inspection of hypoperfusion changes showed most prominent involvement in the cerebral midline structures. However, hemispheric asymmetries in the right and left TLE groups were also present, such as significant contra-lateral hypoperfusion of the temporo-parietal junction, which was present in the right but not the left TLE group. Hyperperfusion of the brainstem tegmentum, implicating involvement of the reticular activating system, is less common in right TLE as compared to left TLE. This finding may explain the differences in degree of loss of consciousness in right as compared to left TLE seizures. Hypoperfusion patterns in the cerebral hemispheres also show asymmetries, which may also play a role in differences in semiology of right and left TLE seizures.