Comment from Professor Dirk Van Roost on: Lesion-focused stereotactic thermo-coagulation of focal cortical dysplasia II-B: A new approach to epilepsy surgery?

The idea of attempting to eliminate epileptogenic foci by stereotactic means is not novel; it has been pursued since the 1960s. A range of ablation techniques has been used: from simple electrocoagulation to thermo-coupled electrocoagulation or radiosurgery, and, most recently, focused ultrasound. If the results of stereotactic treatment for epilepsy surgery have not been completely convincing in the past, this was not due to inaccuracy of the stereotactic technique, but because there was an insufficient understanding of the epileptogenic zone and because there was a mismatch between the very confined stereotactic ablations and the usually larger epileptogenic zones. However, stereotactic treatment approaches have adjusted to this evolving understanding and radiosurgery for epileptogenic hamartomas or for mesial temporal lobe epilepsy has emerged as a valuable alternative surgical treatment method. Hence, the controversy is not about the use of stereotaxis in the treatment of epilepsy, but about the extension of the epileptogenic zone in relation to the borders of an epileptogenic lesion. Perfect congruence between both has been established for some epileptogenic lesions, such as hypothalamic hamartomas and periventricular nodular heterotopias, which, hence, have become amenable to highly focused stereotactic radiosurgery and thermocoagulation, respectively. Wellmer, Kopitzki, and Voges now suggest that focal cortical dysplasias type IIB may be another type of epileptogenic lesion whose MRIextension may be congruent with the epileptogenic zone, making such lesions suitable targets for stereotactic thermocoagulation, especially when open resection would be difficult or risky, when they are singular and small enough for this approach. The penetration of a stereotactic probe into the brain parenchyma and the focal cortical dysplasia is not completely devoid of any risk, compared to, for example, radiosurgery. However, it offers the possibility of registering epileptic activity in situ and of eliciting evoked potentials, which could improve outcome in terms of better seizure control and function preservation, respectively.