The value of PET scan (and MRI and Wada test) in patients with bitemporal epileptiform abnormalities

Lateralization remains difficult in patients with bitemporal epileptiform abnormalities.

To evaluate the reliability of the interictal fluorodeoxyglucose F18-positron emission tomographic (PET) scan in this setting.

We analyzed PET scan findings in 25 patients who required bilateral depth electrodes for lateralization of temporal lobe epilepsy. The contribution of magnetic resonance imaging and the intracarotid amobarbital procedure was also analyzed.

Positron emission tomographic scan revealed lateralized hypometabolism in 15 patients. This was in agreement with the depth evaluation in 10 cases (67%). In five cases (33%), the PET and depth findings were in disagreement, with no predominant side of seizure origin by depth electroencephalography (EEG) in four cases and PET lateralization opposite to depth findings in one case. In 10 of the 25 patients, PET scans could not lateralize hypometabolism to one temporal lobe, of which six were confirmed by depth EEG not to have a predominant side of seizure onset. The overall sensitivity of PET for concordant lateralized seizure onset was 67%. Ten of 14 patients who underwent a lobectomy had a successful outcome, including three of four patients whose temporal lobe epilepsy was lateralized by depth EEG but not by PET. One patient had PET lateralization opposite to the depth EEG and side of surgery and failed to improve.

In this highly selected group of patients, the lateralizing value of PET and magnetic resonance imaging was somewhat diminished, and the intracarotid amobarbital procedure was not found useful for lateralization. Positron emission tomography and magnetic resonance imaging, when pointing to the side opposite depth EEG, may indicate a poor prognosis.