Ictal brain perfusion SPECT in the preoperative evaluation of intractable temporal lobe epilepsy

Learning Objectives 1. Understand the technique and procedural logistics of ictal SPECT 2. Provide examples of imaging findings and their management implications. 3. Discuss the advantages and limitations of this modality.

Summary: Epilepsy affects approximately 3% of the population. About 30% of cases are intractable seizures, and most of them have a focal origin, often in the temporal lobe (TLE). Surgery is the best therapeutic option for refractory TLE.Presurgical planning aims to identify the ictal onset zone, define optimal resection borders to balance seizure relief and neuropsychological deficits. In addition to video-EEG monitoring, neuropsychological evaluation and MRI, ictal SPECT provides another noninvasive tool in epilepsy preoperative evaluation. Ictal SPECT is used to localize the epileptogenic zone, and is particularly useful in MRI-negative partial epilepsy and focal cortical dysplasias. During epileptic activity, hyperperfusion of the seizure onset zone occurs because of autoregulatory response. Visual comparison of the ictal and interictal SPECT is used in study interpretation. After IV injection, tracer reaches the brain in 15-20 sec. Therefore, ictal SPECT may display not only the ictal onset zone, but also areas of seizure propagation. Thus, timely tracer injection after seizure onset and awareness of propagation patterns are crucial for accurate interpretation of ictal SPECT. The technique and procedural logistics will be described and examples of ictal onset zone and propagation pathways will be presented. We believe that ictal SPECT should be the first line modality in the preoperative evaluation of intractable epilepsy.