Use of Innovative SPECT Techniques in the Presurgical Evaluation of Patients with Nonlesional Extratemporal Drug-Resistant Epilepsy

Table 1

Summary of the function and localization ability of all the functional imaging modalities.

Type of SPECT study	Function	Localization rate of a seizure focus	Strengths	Limitations
Interictal SPECT	Shows hypoperfusion or normal perfusion in the epileptogenic region interictally.	50% [61, 62]	Provides a baseline interictal perfusion scan to be used for comparison with the ictal SPECT.	It cannot reliably be used alone in defining a seizure focus.
Ictal SPECT	Shows an area of hyperperfusion in the epileptogenic region, surrounded by an area of hypoperfusion, during the seizure.	Up to 97% of cases with known unilateral temporal lobe epilepsy and up to 90% with known or suspected extratemporal lobe epilepsy [51–54].	Superior to interictal SPECT in its ability to localize the seizure focus	Late injections can show areas of propagation rather than the seizure onset zone [56, 57].
SISCOM	Uses computer-aided subtraction of interictal from ictal SPECT and then co-registers it to the MRI.	88% [48]; Up to 92% [67]	Increases the seizure focus detection rate and guides the extent of resection in extratemporal lobe epilepsy surgery and can also predict postsurgical outcome [67–69].	Does not determine whether the ictal-interictal subtraction difference is statistically different from the expected random variation between two SPECT studies [73, 74].
STATISCOM/SPM	Determines the statistical significance of perfusion changes in epilepsy patients by comparison to a control group without epilepsy, and so it compensates for the physiologic variance in cerebral blood flow.	71 to 83% [66]; Superior to SISCOM [73–75]	Compensates for the physiologic variance in cerebral blood flow that shows significant asymmetries in multiple areas.	Both sensitivity and specificity of SPM-SPECT remain unclear when used in a population of unselected patients with normal MRI focal epilepsy, like in nonlesional ETLE [74, 75].
PISCOM	Uses interictal PET and subtracts ictal SPECT and then co-registers it on MRI.	No significant difference compared to SISCOM [76].	Showed a lower amount of indeterminate activity due to propagation, background, or artifacts [76].	The need to use two functional studies; interictal PET and ictal SPECT