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.