Unilateral thalamic hypometabolism in patients with temporal lobe epilepsy.

Background/purpose: Interictal brain 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET) is useful for localizing the focus of a seizure, and thalamic hypometabolism has been observed in temporal lobe epilepsy (TLE). In this study, we aimed to investigate the prevalence of thalamic hypometabolism and to assess the usefulness of this supplementary finding for lateralizing epileptic foci on FDGPET scans in patients with TLE.

Methods: This was a retrospective study of 47 patients who underwent anterior temporal lobectomy to treat medically intractable TLE. Other inclusion criteria were age older than 18 years, preoperative interictal FDG-PET, no structural abnormality (except for mesial temporal sclerosis) on preoperative magnetic resonance imaging, and seizure-free status (Engel class I) for at least 2 years after the operation. The presence and location of hypometabolism on FDG-PET scans were recorded.

Results: Of the 47 patients examined, 12 were subsequently excluded. Concomitant hypometabolism in both the temporal lobe and the ipsilateral thalamus was observed on FDG-PET scans in seven (20%) of the remaining 35 patients. One patient had thalamic hypometabolism contralateral to the hypometabolic temporal lobe.

Conclusion: Ipsilateral thalamic hypometabolism is a supplementary finding on FDG-PET scans in patients with TLE and can aid in lateralizing epileptic foci during FDG-PET. However, in rare cases, hypometabolism of the contralateral thalamus can occur and cause false lateralization.