Predicting seizure-free status for temporal lobe epilepsy patients undergoing surgery: prognostic value of quantifying maximal metabolic asymmetry extending over a specified proportion of the temporal lobe.
Conventional visual analysis of brain (18)F-FDG PET scans is useful for predicting postsurgical improvement for temporal lobe epilepsy (TLE) patients, but prognostic value for identifying patients who will achieve seizure-free status is considerably lower. We aimed to develop an approach with which to quantitatively assess prognostically pertinent aspects of metabolic asymmetry in presurgical PET scans for forecasting postsurgical seizure-free clinical outcomes.


METHODS
Presurgical brain PET scans of 75 TLE patients were examined using a display/analysis tool that quantified maximal metabolic asymmetry in a specified proportion (x%) of the temporal lobe pixels in the most asymmetric plane, generating a temporal lobe asymmetry index (T-AI(x)). Results of this analysis were compared with patients' actual postsurgical outcomes after an average of approximately 4 y of clinical follow-up. The investigation was divided into 2 main steps: The PET scans examined in the first step, selected by chronological order of scan acquisition dates, comprised just less than two thirds of the patient group studied (n=47) and were used to look for parameters predicting seizure-free postsurgical outcome; in the second step, the predictive value of the parameters suggested by the analysis in the first step was independently examined using the set of remaining PET scans (n=28) to check for wider applicability of the approach.


RESULTS
Of the 75 patients studied, 42 became seizure free after surgery, whereas 33 continued to seize beyond the immediate postoperative period, during a mean 3.8-y follow-up interval. The specified proportion of temporal pixels with which to assess maximal asymmetry that provided the highest prognostic value with respect to achieving seizure-free status was 20%. Across the study population, those patients with scans having lower T-AI(20) values (corresponding to <40% difference in pixel intensities between left and right temporal lobes, among the 20% most asymmetric left-right pixel pairs measured in the most asymmetric plane) were only half as likely to continue to have seizures postsurgically as those with scans having higher T-AI(20) values (positive likelihood ratio for achieving seizure-free outcome, 1.98; 95% confidence interval, 1.07-3.67). Overall, those patients with greater maximal asymmetry, as indexed by higher T-AI(20) values, had a significantly decreased chance of achieving seizure-free status after surgery than those with lower degrees of asymmetry (P=0.017), and this same tendency was observed for both the first and second series of PET scans examined.


CONCLUSIONS
A quantifying approach to assessing maximal temporal asymmetry over a specified proportion of the temporal lobe may help to predict whether patients will likely be free of seizures during the years after neurosurgical resection of epileptogenic tissue.
Lin
Tina W
TW
Department of Molecular and Medical Pharmacology, David Geffen School of Medicine, UCLA, Los Angeles, CA 90095-6942, USA.
de Aburto
Michelle A Kung
MA
Dahlbom
Magnus
M
Huang
Lynn L
LL
Marvi
Michael M
MM
Tang
Michael
M
Czernin
Johannes
J
Phelps
Michael E
ME
Silverman
Daniel H S
DH
D000328:Adult; D000465:Algorithms; D001921:Brain / Q000000981:diagnostic imaging / Q000378:metabolism; D004833:Epilepsy, Temporal Lobe / Q000000981:diagnostic imaging* / Q000378:metabolism* / Q000601:surgery*; D005260:Female; D019788:Fluorodeoxyglucose F18 / Q000493:pharmacokinetics*; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008297:Male; D049268:Positron-Emission Tomography / Q000379:methods*; D011379:Prognosis; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D016896:Treatment Outcome
D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18