Although interictal hypoperfusion and ictal hyperperfusion are established localizing findings in partial epilepsy, their relative value is disputed. After a meta analysis of several published articles on SPECT brain imaging in patients with epilepsy (with extractable data on at least 6 patients per article), institutions using SPECT for evaluation of epilepsy have been encouraged to perform ictal scanning or interictal and postictal SPECT studies.
Methods: We compared the relative localizing values of hypoperfusion in video-electroencephalographically (EEG) monitored interictal SPECT (IISPECT) and hyperperfusion in immediate postictal or periictal SPECT (PISPECT) in nonlesional patients who underwent temporal lobectomies in our epilepsy center from 1995 to 1998. We also evaluated the usefulness of combined interpretation of IISPECT and PISPECT when available.
Results: Our experience with continuous cerebral blood-flow monitoring, published elsewhere, and SPECT results indicate that these recommendations are valid, but obtaining ictal SPECT is often serendipitous. We found that (a) interictal hypoperfusion was easier to demonstrate by SPECT but was less often concordant with the EEG focus than hyperperfusion in PISPECT, but not significantly (P = 0.11) so; (b) the lower incidence of hyperperfusion in PISPECT in our series was due to the occurrence of hypoperfusion in PISPECT, which was seen in 34.5% of our patients; and (c) hypoperfusion in PISPECT did have localizing value when it occurred on the same side as the hypoperfusion noted in IISPECT.
Conclusion: On the basis of our findings, we recommend the use of 3 distinct perfusion patterns that emerge from the combined interpretation of IISPECT and PISPECT we proposed earlier (patterns 1-3), for localization purposes when possible, rather than ictal SPECT, IISPECT, or PISPECT by itself.