Secondary epileptogenic lesions.

SUMMARY In a large series of animals the development of secondary epileptogenic lesions was subjected to specific study. The time course and topographic features were delineated. Characteristic differences were noted for lesions in motor as opposed to visual cortex. The effect of callosal transection as well as the typical topography indicate that the callosal pathway is an essential and probably the major route of propagation for the secondary lesions investigated. However there is considerable evidence which suggests that extracallosal pathways play an important facilitatory role. The effect of excision of the primary lesion and of callosal transection on the disappearance or persistence of secondary discharge was demonstrated. Although considerable “success” attended these interventions at the earlier intervals, the same procedure undertaken later in the course of disease had no apparent influence. Indeed, callosal transection may have had an adverse effect since there were fewer remissions than would be expected had there been no “treatment” at all. It was found that electrographic criteria of dependence or independence of a secondary discharge had no prognostic validity with respect to surgical outcome. However, experiments with intracarotid amytal indicated that the electrographic change in the mirror region induced by contralateral (primary side) injection had a high degree of predictive value. While caution is advocated in extrapolating this finding to human clinical problems, the evidence would seem to warrant a clinical trial of the method. This technique for production of secondary epileptogenic lesions at a considerable distance from the site of direct intervention provides an experimental model which should prove useful for investigation of basic cellular alterations involved in epileptiform electrogenesis. RESUME Le developpement de lesions epileptogeniques secondaires a ete l'objet de l'etude specifique d'une importante serie d'animaux. Les changements dans le cours du temps et les caracteristiques topographiques ont ete decrits. Il a ete observe des differences caracteristiques de lesions dans le cortex moteur en opposition avec le cortex visuel. L'effet d'une transection du corps calleux indique, tout aussi bien que la topographie typique, que la voie calleuse est la voie essentielle et, probablement, la voie principale de la propagation des lesions secondaires etudiees. Toutefois, on peut penser selon une vraisemblabilite considerable que les voies extra-calleuses jouent ici un role important pour faciliter l'apparition de ces phenomenes. Demonstration de l'effet de l'excision de la lesion primaire et de la transection calleuse sur la disparition ou la persistance de la decharge secondaire. Bien qu'un “succes” considerable ait ete obtenu par ces interventions dans un stade precoce, la meme mesure prise au cours d'un stade plus avance de la maladie n'a pas eu d'influence apparente. La transection calleuse, en effet, peut avoir exerce une action defavorable puisqu'il y a eu encore moins de remissions que s'il n'y avait pas eu de “traitement”. Il a ete constate que les criteria electrographiques de dependance ou independance d'une decharge secondaire est sans valeur de pronostic quant au resultat chirurgical. Toutefois, des experiences pratiquees sur l'amytal intracarotidien indiquent que le changement electrographique induit dans la region du miroir par injection contra-laterale (cote primaire) a ete hautement prophetique. Tandis que la prudence est a conseiller dans l'extrapolation de cette decouverte aux problemes cliniques humains, l'experience semble justifier un essai clinique de la methode. Cette technique de la production de lesions epileptogenes secondaires a une distance considerable du terrain de l'intervention directe, fournit un exemple experimental susceptible d'utilite dans la recherche des alterations cellulaires basales impliquees dans Pelectrogenese epileptiforme.