Abtin Doroudinia MD*, Mehrdad Bakhshayesh Karam MD, Abbas Yousefi Koma MD, Jafar Mehvari MD, Sohrab Fesharaki MD

National Research Institute of Tuberculosis and lung diseases (NRITLD), Masih Daneshvari Hospital, Tehran-Iran

Objectives:

About one third of patients with partial epilepsy does not respond to pharmacotherapy and in selected cases may benefit from surgery; therefore identification of structural lesions is vital in the pre-surgical evaluation. Brain MRI fails to reveal apparent abnormality in approximately 20% of patients with medically refractory epilepsy. FDG PET/CT is highly sensitive in localizing epileptogenic foci and is able to provide information complementary to MRI imaging.

Material and methods:

This is a cohort study aiming to evaluate patients suffering from refractory epilepsy, referred by 2 expert neurologist colleagues. All patients are evaluated clinically with EEG to localize epileptogenic focus in the brain cortex. All patients must have an unremarkable brain MRI. FDG PET/CT of brain has been performed in all cases with normal brain MRI to help localizing epileptogenic focus.  The PET/CT images were evaluated by 2 nuclear medicine and radiologists simultaneously in search for possible hypometabolic (decreased metabolic activity) focus which could be suggestive for epileptogenic region in the brain cortex. We used expert visual analysis method to evaluate brain cortex metabolic activity. Finally, the clinical and EEG data together with PET/CT imaging results were compared to determine degree of data congruency. The findings were stratified as exactly congruent, partially congruent and incongruent. Also we stratified patients with regard to clinical epileptogenic focus as localized in temporal lobe, frontal lobe or partially localized and tried to find out in which group of patients PET/CT is most congruent with clinical and EEG findings.

Results and discussion:

In this study we included 99 patients (50 male and 49 female) with mean age of 27.95 years (ranging between 5 and 60 years).

63 patients had their seizure focus localized in temporal lobe by means of clinical and EEG evaluation in which 32 of them demonstrated exactly congruent PET/CT results (50.8%). Remainder of these patients demonstrated either partially congruent PET/CT results (7 patients, 11.1%) or totally incongruent PET/CT findings (24 patients, 38.1%).

24 patients had their seizure focus localized in frontal lobe by means of clinical and EEG evaluation in which only 3 (12.5%) of them demonstrated partial congruency with PET/CT results. The remainder of 21 (87.5%) patients demonstrated incongruent PET/CT results and there was no case in frontal lobe focal seizures with congruent PET/CT results.

12 patients had their seizure focus only partially localized in one hemisphere in which 6 (50%) patients demonstrated partial congruency with PET/CT results.  

Evaluation of our PET/CT scans demonstrated 34 negative brain PET in which 17 patients (50%) had their seizure focus localized in temporal lobe, 11 patients (32.3%) in frontal lobe and 6 patients (17.7%) only partially localized on clinical and EEG evaluation.

All exact congruent PET/CT results had their seizure focus localized in temporal lobe. Among partially congruent cases; 7 patients (38.9%) had their seizure focus localized in temporal lobe, 4 patients (22.2%) in frontal lobe and 7 other patients (38.9%) only partially localized.

Although 50% of temporal lobe seizure patients demonstrated exactly congruent PET/CT results, but these results may be further enhanced by means of more precise localization of seizure focus on clinical and EEG evaluations, in addition to using more advanced PET/CT imaging software which enables the diagnostician to quantify image findings.

Over all PET/CT results in frontal lobe or partially localized patients are not promising in our study and further studies with larger sample size are required.

Also the fact that significant number of partially congruent cases had been partially localized on clinical and EEG evaluation (38.9%); in addition to 50% congruency in partially localized cases, also emphasizes on performing more precise clinical and EEG evaluation in patients to exactly localized seizure focus.   

Conclusion:

FDG PET/CT is useful tool to evaluate patients with refractory seizure who had localized seizure in temporal lobe on clinical evaluation. Utility of FDG PET/CT scan in extratemporal seizure foci is much more limited.

The more precise is the localization of seizure focus on clinical and EEG evaluation; the more helpful would be the subsequent PET/CT scan to confirm that finding which would be to the patient’s best interest to be candidate for possible ablation surgery.

Our results need to be further validated in larger studies.