F-18-FDG PET studies in patients with extratemporal and temporal epilepsy:Evaluation of an observer-independent analysis

The aim of this study was to evaluate an observer-independent analysis of F -18-fluorodeoxyglucose (FDG) PET studies in patients with temporal or extra temporal epilepsy. Methods: Twenty-seven patients with temporal epilepsy an d 22 patients with extratemporal epilepsy were included in the study. All p atients with temporal epilepsy and 7 patients with extratemporal epilepsy u nderwent surgical treatment. In patients who showed significant postoperati ve improvement (temporal, n = 23; extratemporal, n = 6), the epileptogenic focus was assumed to be located in the area of surgical resection. In extra temporal epilepsy patients who did not undergo surgery, the focus localizat ion was determined using a combination of semiology, ictal and interictal e lectroencephalography, [Tc-99m]ethyl cysteinate dimer SPECT, MRI and [C-11] flumazenil PET. Visual analysis was performed by two experienced and two le ss experienced blinded observers using sagittal, axial and coronal images. In the automated analysis after anatomic standardization and generation of three-dimensional stereotactic surface projections (SSPs), a pixelwise comp arison of F-18-FDG uptake with an age-matched reference database (n = 20) w as performed, resulting in z score images. Pixels with the maximum deviatio n were detected, summarized and attached to one of 20 predefined surface re gions of interest. For comparison with F-18-FDG PET and MR images, three-di mensional overlay images were generated. Results: In patients with temporal epilepsy, the sensitivity was comparable for visual and observer-independe nt analysis (three-dimensional SSP 86%, experienced observers 86%-90%, less experienced observers 77%-86%). In patients with extratemporal epilepsy, t hree-dimensional SSP showed a significantly higher sensitivity in detecting the epileptogenic focus (67%) than did visual analysis (experienced 33%-38 %, each less experienced 19%). In temporal lobe epilepsy, there was moderat e to good agreement between the localization found with three-dimensional S SP and the different observers. In patients with extratemporal epilepsy, th ere was a high interobserver variability and only a weak agreement between the localization found with three-dimensional SSP and the different observe rs. Although three-dimensional SSP detected multiple lesions more often tha n visual analysis, the determination of the highest deviation from the refe rence database allowed the identification of the epileptogenic focus with a higher accuracy than subjective criteria, especially in extratemporal epil epsy. Conclusion: Three-dimensional SSP increases sensitivity and reduces o bserver variability of the analysis of F-18-FDG PET images in patients with extratemporal epilepsy and is, therefore, a useful tool in the evaluation of this patient group. The benefit of this analytical approach in patients with temporal epilepsy is less apparent.