Cortical dysplasias and epilepsy: a review of the architectonic, clinical, and seizure patterns

Abstract

Since the nineteenth century, various abnormalities of cortical development resulting from migration defect, disorders of maturation, and disorders of cortical organization were described in brains at autopsy. Cortical dysplasia then was recognized in tissue resected during surgical treatment of patients with intractable epilepsy, but this finding remained largely unappreciated until the development of modern imaging. CT allowed glimpses of the more obvious malformations, but it was the advent of MRI that enabled the recognition and classification of the different types of lesions. In the Taylor type of cortical dysplasia, it became clear that there was a wide range in the severity and, above all, in the extent of the abnormality. The lesions range from small areas, often difficult to identify, to extensive lesions surrounded by a halo or penumbra of presumably less severe, but still clinically significant, structural abnormality. Functional imaging (SPECT, PET, and MRS) have provided additional insights and led to strategies for surgical treatment. Even lesions involving the central strip may at times be successfully resected, but in such patients much depends on the preoperative neurologic status. Recognition of the fact that dysplastic lesions are in themselves epileptogenic has been another milestone in our understanding of these abnormalities. Subcortical heterotopias, in particular periventricular nodular heterotopias, have been recognized as causing intractable epilepsy in some but not in all patients. Surgical approaches to these lesions are now being planned. The hereditary nature of the lesions in some patients has explained the familial occurrence of epilepsy in a number of instances. Generalized epileptic abnormalities and generalized disorders of migration and maturation have been described as band heterotopia or the double-cortex syndrome. Here, too, sex-linked dominant inheritance may occur, and progress has been made in our understanding of the mechanisms of these genetically determined lesions. Focal resection in patients with band heterotopia, however, has been of little value in the small number of patients in whom it has been carried out. Cortical malformations due to disorganization, occurring later in intrauterine life, are represented by micropolygyria. These lesions are often bilateral and perisylvian, but at times they are unilateral and in some patients may be occipital or frontal. Several syndromes have emerged, the most common being the one characterized by severe pseudobulbar palsy and mild pyramidal deficit (31). In some patients with such cortical abnormalities, particularly those with micropolygyria, the epilepsy may not be intractable, and full control may be obtained by medical treatment (32). Interesting and important clinical features of patients with bilateral perisylvian polymicrogyria were described by Guerrini et al. (33) and Caraballo et al. (34). In some patients who develop a secondary generalized electrographic abnormality and drop attacks early in the first decade, there is eventual improvement and cessation of the epileptic abnormality toward the end of the first decade or somewhat later. These investigators stressed that callosotomy should be considered with caution in patients with micropolygyria and this electroclinical pattern. Hypothalamic hamartomata and the associated epileptic syndrome have been better understood in recent years. Despite the risks of surgery, resection of the lesion offers hope of improvement in seizure control and of the often extremely severe behavioral abnormalities. On the other hand, patients with small lesions leading only to a "need to laugh" without more overt epileptic or behavioral manifestations are now being recognized. Finally, initial investigations have begun to uncover the transmitter abnormalities in patients with cortical dysplasia. (ABSTRACT TRUNCATED)