Single Photon Emission Computed Tomography (SPECT) in Epilepsies

Abstract

Brain perfusion SPECT is a well-established clinical nuclear medicine neuroimaging modality increasingly used in the pre-surgical evaluation of epileptogenic foci/zones for patients with medically refractory focal (partial) seizures. In comparison to ictal SPECT scans, interictal SPECT studies are easy to perform and typically show asymmetric focal/regional cortical hypoperfusion that is suspicious for an interictal epileptogenic focus/zone. However, the positive detection sensitivity is only about 50%, whereas false-negative findings could occur in the remaining 50% of patients (Gaillard, Wyllie’s treatment of epilepsy: principles and practice. Wolters Kluwer, Philadelphia, 2011). In contrast, ictal SPECT scans reveal seizure-induced focal cortical hyperperfusion as a positive finding. Due to the unpredictability of epilepsy onset in terms of timing, seizure types, and seizure duration, as well as a limited radioactive tracer injection window, ictal SPECT scans are difficult to perform but have an improved positive detection sensitivity of 67–90% (Gaillard, Wyllie’s treatment of epilepsy: principles and practice. Wolters Kluwer, Philadelphia, 2011; Kumar and Chugani, Pediatric epilepsy surgery preoperative assessment and surgical treatment. Thieme, New York, 2010). Due to seizure propagation, however, interpretation of ictal SPECT studies is often challenging. SISCOM (subtraction of ictal SPECT coregistered to MRI) is an imaging application that subtracts ictal study from interictal study, and coregisters the difference (also called delta results) to the patient’s brain MRI for anatomic localization of epileptogenic foci/zones (O’Brien et al., Nucl Med Comm 19:31–45, 1998; O’Brien et al., Neurology 52:137–146, 1999; von Oertzen et al., Epilepsia 52:2239–2248, 2011). Selected cases in this chapter show the value and limitation of interictal SPECT studies alone or the combined imaging approach, e.g., ictal/interictal SPECTs and subsequent SISCOM analysis, in the evaluation of temporal lobe epilepsies (TLEs), extratemporal lobe epilepsies, and bifocal/multifocal epilepsies and in the pre-surgical workup of focal cortical dysplasia (FCD)-induced medically refractory epilepsy in an MRI-normal patient, as well as an epilepsy patient with known tuberous sclerosis (TS).