Surgical treatment of epilepsy: the problem of lesion/focus incongruence

This study suggests an alternative surgical strategy for treating patients with intractable epilepsy in whom a lesion, visualized by imaging, is found to be at a distance from the maximal electroencephalographic abnormality (focus).

Sixty patients (divided into three groups of 20), all of whom have had surgical resection for intractable epilepsy, are reviewed. Group A patients, representing the most common situation of a congruent electroencephalographic focus and structural lesion, underwent resection of the lesion/focus. Group B patients, in whom the focus and the lesion are incongruent, underwent resection of the focus only. Group C patients are those where the focus and lesion are incongruent; in this group, the lesion only was resected.

Group A patients underwent resection of the lesion/focus (sites: 13 temporal, six frontal, and one parietal) with excellent results. Group B patients, in whom the focus only was resected (lesion sites: 14 temporal, four parietal, and two occipital) obtained poor results. Group C patients had excellent results following resection of the lesion only (lesion sites: 12 temporal, seven frontal, and one parietal). The superior surgical outcome in seizure control of group C is comparable to that seen in group A (Chi2 contingency test; Chi2 = 3.27 p > .05, 3 degrees of freedom) and is in contrast to the poor results seen in group B (Chi2 = 20.59 p < .001, 3 degrees of freedom).

In those patients where a choice between a focus and a lesion is imperative, the lesion detected by imaging should be given priority in surgical resection.