Histopathological correlates of epileptogenicity as expressed by electrocorticographic spiking and seizure frequency

To study the correlation between histopathology and epileptogenicity, as measured by seizure frequency and electrocorticography (EcoG), in patients with cortical dysplasia (CD) as compared with control patients with gangliogliomas or gliomas.

The influence of the histopathological classification and the presence of balloon cells in CD on the frequency and extension of five predefined patterns of ECoG spiking, seizure frequency, age of seizure onset and 6-month postoperative outcome were analyzed in 32 patients with focal epilepsy undergoing presurgical evaluation with chronically implanted subdural electrodes.

Comparison of patients with CD, gangliogliomas, and gliomas showed that the seizure frequency was greatest in patients with CD and ECoG spiking and was most extensive in patients with gangliogliomas. The onset of epilepsy was earlier in patients with CD and with gangliogliomas. None of these differences was significant. However, in patients with CD, the presence of balloon cells was associated with significantly 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 with the duration of the epilepsy and the number of seizures recorded during monitoring. No significant correlation was detected between histopathology, seizure frequency, or ECoG activity and postoperative outcome, which was relatively favorable in patients with balloon cells.

CD refers to a variety of histopathological patterns associated with different epileptogenicity. In CD, increased clinical and ECoG epileptogenicity correlates with the presence of balloon cells. This finding confirms that balloon cells should be considered in the histopathological classification of CD. The predefined ECoG were not specific for any of the histopathologies investigated.