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

Objective: To determine whether the detection of focal hypoperfusion by subtraction SPECT coregistered to MRI (SISCOM) improves the sensitivity and specificity of postictal SPECT in intractable partial epilepsy. Background: Postictal SPECT injections are easier to perform than are ictal injections, but the images are more difficult to interpret and have been reported to have lower sensitivity and specificity. Methods: Thirty-five consecutive intractable partial epilepsy patients who had postictal SPECT studies were evaluated. The following sets of SPECT images were separately interpreted by three blinded reviewers and classified as either localizing to 1 of 16 possible sites in the brain or as nonlocalizing: unsubtracted postictal and interictal images for conventional side-by-side comparison, SISCOM images of hyperperfusion, SISCOM images of hypoperfusion, and both sets of SISCOM hyperperfusion and hypoperfusion images (combined SISCOM evaluation). Results: Significantly higher proportions of the hyperperfusion SiSCOM images (65.7%), the hypoperfusion SISCOM images (74.3%), and the combined SISCOM evaluation (82.9%) were localizing than were the conventional method of side- by-side comparison of unsubtracted images (31.4%; p < 0.0001). Concordance with the discharge diagnosis was higher for the combined SISCOM evaluation than it was for either the hyperperfusion or the hypoperfusion SISCOM images alone (both p < 0.05). For the hypoperfusion SISCOM and the combined SISCOM evaluations, 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 hyperperfusion, improves the sensitivity and specificity of postictal SPECT in intractable partial epilepsy.