Presurgical multimodality neuroimaging in electroencephalographic lateralized temporal lobe epilepsy

Abstract

The purpose of this study was to compare 2-[18F]fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET), hippocampal volumetry (HV), T2 relaxometry, and proton magnetic resonance spectroscopic imaging (1H-MRSI) in the presurgical neuroimaging lateralization of patients with nonlesional, electroencephalogram (EEG)-defined unilateral temporal lobe epilepsy (TLE). Twenty-five patients were prospectively studied, along with age-matched controls. T2 relaxometry examinations were performed in 13 patients. Comparison of FDG-PET, HV, and 1H-MRSI was possible in 23 patients. FDG-PET lateralized 87% of patients, HV 65%, N-acetyl aspartate (NAA)/(choline [Cho] + creatine [Cr]) 61%, and [NAA] 57%. Combined HV and NAA/(Cho + Cr) results lateralized 83% of the patients, a value similar to PET. Of 10 patients with normal magnetic resonance imaging (MRI) scans, 2 were lateralized with HV, 6 with FDG-PET, 4 with NAA/(Cho + Cr), and 3 with [NAA]. T2 relaxometry lateralized no patients without hippocampal atrophy. Bilateral abnormality was present in 29 to 33% of patients with 1H-MRSI measures and 17% with HV. Only hippocampal atrophy correlated with postoperative seizure-free outcome. FDG-PET remains the most sensitive imaging method to correlate with EEG-lateralized TLE. Both FDG-PET and 1H-MRSI can lateralize patients with normal MRI, but only the presence of relative unilateral hippocampal atrophy is predictive of seizure-free outcome. Bilaterally abnormal MRI and 1H-MRSI measures do not preclude good surgical outcome.

Fig 1

Proton magnetic resonance spectroscopic imaging spectra from right and left homotopic voxels (one of five hippocampal voxels included for analysis). Inset shows the voxel locations on magnetic resonance imaging with coregistered 2-[¹⁸F]fluoro-2-deoxy-d-glucose positron emission tomography. This patient had left temporal lobe epilepsy with concordant hippocampal atrophy. All modalities provided correct lateralization, and the patient became seizure free after surgery. Cho = choline; Cr = creatine; NAA = N-acetyl aspartate.

Fig 2

Lateralization achieved with positron emission tomography (PET) and N-acetyl aspartate (NAA)/(choline [Cho] + creatine [Cr]) is compared in patients with (A) and without (B) hippocampal volumetry–defined hippocampal atrophy. The roman numerals within the circles designate each patient's surgical outcome classification defined by Engel [24]. (A) As can be seen, PET lateralized 14 of 15 patients with hippocampal atrophy, compared with 10 of 15 by NAA/(Cho + Cr). In patients without atrophy (B), PET lateralized 6 of 8, compared with 4 of 8 by NAA/(Cho + Cr). Note: Two patients, 1 without 2-[¹⁸F]fluoro-2-deoxy-D-glucose (FDG)-PET data (class III outcome) and another without proton magnetic resonance spectroscopic imaging data (class I outcome), are not shown in A.