PET imaging of brain 5-HT1A receptors in the preoperative evaluation of temporal lobe epilepsy

Abstract

[¹⁸F]MPPF PET has previously been used to identify the epileptic lobe in temporal lobe epilepsy (TLE) patients at the group level. This study aims to validate the visual analysis of [¹⁸F]MPPF PET in the assessment of individual TLE patients for their suitability to undergo temporal lobe resection. Forty-two patients suffering from TLE and 18 control subjects matched for age and gender were prospectively enrolled for [¹⁸F]MPPF PET. Four subtypes were defined according to the presurgical evaluation: mesio-TLE (MTLE, 32 patients), temporal neocortical epilepsy (NC, five patients), temporo-perisylvian epilepsy (T+, three patients) and temporal epilepsy without further information (t, two patients). Parametric binding potential (BP_ND) images were obtained using a simplified reference tissue model. Three examiners, who were blinded to other data, visually interpreted each scan and delineated areas of decreased [¹⁸F]MPPF BP_ND. Statistical parametric mapping (SPM) analysis of MPPF BP_ND images was also performed. Visual analysis showed a low rate of disagreement between the three examiners (7%). PET scans were considered normal in four patients (9.5%). In the remaining 38 patients (90.5%), areas of focal BP_ND decrease were identified. A specific pattern was encountered in the MTLE subgroup, consisting of a BP_ND decrease involving hippocampus, amygdala and temporal pole altogether. Combining the results from the presurgical investigations and the surgical outcome, we estimated that the area of BP_ND decrease coincided with the epileptogenic zone in 40% of patients in the MTLE subgroup and 33% in the other TLE subtypes. This relatively low precision was due to 47% of patients who showed BP_ND decreases in the insula ipsilateral to the epileptogenic lobe. The SPM analysis had much lower sensitivity (67%) to detect BP_ND decreases in the epileptogenic temporal lobe, but revealed areas of increased BP_ND outside the epileptogenic zone and bitemporal BP_ND decreases of undetermined clinical significance, which were undetectable by visual analysis, in 29% of patients. In conclusion, visual analysis of [¹⁸F]MPPF BP_ND images helps in the correct identification of the epileptogenic temporal lobe in all patients showing BP_ND decreases, with a false negative rate inferior to 10% and no false positives in control subjects. All TLE patients with [¹⁸F]MPPF BP_ND decreases involving hippocampus, amygdala and temporal pole together, with or without extension to the ipsilateral insula, were good candidates for anterior temporal lobectomy. All these patients became seizure free after surgery, even when the clinical presentation was not that of a typical MTLE, or when MRI failed to detect hippocampal atrophy.