HISTOPATHOLOGICAL CORRELATES OF EPILEPTOGENICITY AS EXPRESSED BY ELECTROCORTICOGRAPHIC SPIKING AND SEIZURE FREQUENCY

Purpose: To study the correlation between histopathology and epileptog enicity, as measured by seizure frequency and electrocorticography (Ec oG), in patients with cortical dysplasia (CD) as compared with control patients with gangliogliomas or gliomas. Methods: The influence of th e histopathological classification and the presence of balloon cells i n CD on the frequency and extension of five predefined patterns of ECo G spiking, seizure frequency, age of seizure onset and 6-month postope rative outcome were analyzed in 32 patients with focal epilepsy underg oing presurgical evaluation with chronically implanted subdural electr odes. Results: Comparison of patients with CD, gangliogliomas, and gli omas showed that the seizure frequency was greatest in patients with C D and ECoG spiking and was most extensive in patients with ganglioglio mas. The onset of epilepsy was earlier in patients with CD and with ga ngliogliomas. None of these differences was significant. However, in p atients with CD, the presence of balloon cells was associated with sig nificantly greater seizure frequency (p = 0.009), and a significantly greater number of electrodes recording continuous frequent spiking (p = 0.03). The presence of continuous very frequent spiking correlated w ith die duration of the epilepsy and the number of seizures recorded d uring monitoring. No significant correlation was detected between hist opathology, seizure frequency, or ECoG activity and postoperative outc ome, which was relatively favorable in patients with balloon cells. Co nclusions: CD refers to a variety of histopathological patterns associ ated with different epileptogenicity. In CD, increased clinical and EC oG epileptogenicity correlates with the presence of balloon cells. Thi s finding confirms that balloon cells should be considered in the hist opathological classification of CD. The predefined ECoG were not speci fic for any of the histopathologies investigated.