Ictal and interictal ECD-SPECT for focus localization in epilepsy

Forty‐one ECD (Technetium‐99m‐ethyl cysteinate dimer) SPECT investigations were undertaken in the course of a presurgical diagnostic work‐up in 23 patients with pharmacoresistant focal epilepsy. In 21 patients, both an ictal and interictal SPECT were conducted. In the patients receiving ictal SPECT the tracer was injected between 7 and 30 s after the seizure onset. Of the interictal SPECTs 17 of 23 showed focal hypoperfusion which was consistent in 17 cases (74%) with the area of the electrophysiological focus (EF) and 6 patients had a normal interictal SPECT. Of the ictal SPECTs 18 of 21 (86%) showed regional hyperperfusion, 18 of them in the same location as the EF. Ictal SPECT showed a hypoperfusion similar to that in interictal SPECT in another 3 patients. In these cases seizure duration was short (28–54 s), so that the tracer reached the brain postictally. Our results show that ictal ECD‐SPECT is an effective method for demonstrating an epileptogenic focus. Possible reasons for false‐negative ictal SPECT results are discussed.