Role of Ictal and Inter-Ictal SPECT in medically refractory epilepsy: post-surgical correlation

The non-invasive neuroimaging methods, such as single-photon emission computed tomography (SPECT), Video electroencephalogram (VEEG), and magnetic resonance imaging (MRI), has changed pre-surgical epilepsy evaluation. The purpose of this present study was to evaluate the role of ictal and interictal brain SPECT in pre-surgical localization of the epileptogenic focus and assess post-operative outcome. Methods and Materials: 740-1110 MBq (20-30 mCi) of Tc-99m ECD was injected during convulsion while being under VEEG monitoring for ictal brain SPECT study and the SPECT images were acquired after 30 minutes. The same procedure was repeated during interictal period. The reconstructed SPECT images were studied by the physician to look for the increased perfusion focus as epileptic focus and same area was studied in interictal SPECT study for normal or hypoperfusion. The correlation with MRI and VEEG was done. The ictal focus was concluded based on concordance of any two investigations out of the three. The postsurgical assessment was done by Engel's classification. Results: Using the Engel's outcome classification system as the standard of reference, MRI was correct in 46.6% (14/30) of patients. Inter-ictal EEG and Ictal-EEG were concordant with the surgical outcome in 36.66% (11/30) and 63.33% (19/30) of patients, respectively. SPECT shows the maximum concordance rate of 80% (24/30). The difference in the concordance rate of SPECT by Fisher's test when compared to both MRI and Inter-ictal EEG was statistically significant (P < 0.01). In patients with normal MRI findings, ictal SPECT showed accurate lateralization in 50% cases. However, ictal VEEG surpassed SPECT in patients with normal MRI and showed accurate localization in 2/2 cases (100%). Conclusions: In cases of epilepsy with bilateral MRI findings, perfusion SPECT is a useful modality for pre-surgical evaluation. Also, cases with discordant evaluation, SPECT can be employed as a supplementary tool for confirmation for seizure focus localization. SPECT also has a potential role in localizing the epileptogenic focus in patients with normal MRI. (author)