Purpose: The non-invasive localisation of insular lobe epilepsy is a challenge. We aimed to determine if ictal SPECT is a reliable adjunctive test in insular cases and to explore its role in the tailoring of intracranial strategies.
Method: From a dataset of patients who underwent SEEG between December 2012 and December 2016, we collected patients with focal insular onset epilepsy. We examined semiology, EEG, PET and SPECT hyperperfusion pattern with SISCOM. We also reviewed relevant literature.
Results: 5 patients were identified, 4 females, from a dataset of 51 patients. Median age of seizure onset was 8 years old (8 months to 10 years). All patients had an ictal SPECT during pre-surgical work-up: median injection time was 7 s (3-17 sec) from clinical onset, and median seizure duration was 42 s (11-85 sec). Insula cortex showed focal hyperaemia in four patients, all bilateral, with the greatest hyperperfusion contralateral to the ictal onset in two cases, using SISCOM threshold at 1.5 standard deviation. Other sites with hyperaemia included basal ganglia and middle temporal gyrus. The SEEG confirmed insular onset seizures in all the cases. All patients had epilepsy surgery and were seizure free at 21 to 50 months follow up. The results from the literature review showed frequent hyperperfusion in structures outside insula and frequently over the contralateral hemisphere.
Conclusions: This study highlights the technical limitations of SPECT when attempting to assess seizures arising from the insula. Our findings and the literature show ictal SPECT can be localising but falsely lateralising in seizures arising from the insula.
Keywords: Insula; Review; SISCOM.
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