Subtraction SPECT co-registered to MRI improves postictal SPECT localization of seizure foci

Objective: To determine whether the detection of focal hypoperfusion by sub traction SPECT coregistered to MRI (SISCOM) improves the sensitivity and sp ecificity of postictal SPECT in intractable partial epilepsy. Background: P ostictal SPECT injections are easier to perform than are ictal injections, but the images are more difficult to interpret and have been reported to ha ve lower sensitivity and specificity, Methods: Thirty-five consecutive intr actable partial epilepsy patients who had postictal SPECT studies were eval uated. The following sets of SPECT images were separately interpreted by th ree blinded reviewers and classified as either localizing to 1 of 16 possib le sites in the brain or as nonlocalizing: unsubtracted postictal and inter ictal images for conventional side-by-side comparison, SISCOM images of hyp erperfusion, SISCOM images of hypoperfusion, and both sets of SISCOM hyperp erfusion and hypoperfusion images (combined SISCOM evaluation). Results: Si gnificantly higher proportions of the hyperperfusion SISCOM images (65.7%), the hypoperfusion SISCOM images (74.3%), and the combined SISCOM evaluatio n (82.9%) were localizing than were the conventional method of side-by-side comparison of unsubtracted images (31.4%; p < 0.0001). Concordance with th e discharge diagnosis was higher for the combined SISCOM evaluation than it was fdr either the hyperperfusion or the hypoperfusion SISCOM images alone (both p < 0.05). For the hypoperfusion SISCOM and the combined SISCOM eval uations, concordance of the localization with the site of epilepsy surgery was associated with a greater probability of an excellent outcome than were nonconcordant/nonlocalizing images (both p < 0.05). Conclusion: The use of SISCOM to detect focal cerebral hypoperfusion, in addition to focal hyperp erfusion, improves the sensitivity and specificity of postictal SPECT in in tractable partial epilepsy.