Malformations of cortical development☆
Section snippets
Suggested imaging sequences/techniques
Identification and proper diagnosis of cortical malformations depends on performing the proper imaging studies and, if possible, performing them at ages that allow optimization of contrast between gray matter and white matter. Magnetic resonance imaging is the most useful single study in this group of patients, as the excellent contrast between gray matter and white matter allows an accurate topologic assessment of gyral and sulcal development, assessment of the junction of the cortex and white
Fundamental embryology of the brain
During the process of closure of the neural tube, the neuroepithelium lining the central canal of the developing embryo is induced to begin a series of cell divisions [3]. This region of dividing cells is called a germinal zone, or germinal matrix [4]. The developing brain has multiple germinal zones, each one producing a specific set of cells that will migrate through the developing brain using a series of guidance signals [5], [6], [7]. The neurons developing in the neocortical germinal zone
Malformations due to abnormal neuronal and glial proliferation or apoptosis
Malformations resulting from abnormal cell proliferation or apoptosis can have abnormal cells due to abnormal cell differentiation, microcephaly from decreased cell proliferation or increased apoptosis, or macrocephaly from increased cell proliferation or decreased apoptosis [1]. Normal function is not seen in the affected portions of these brains [17]. The major malformations in the group are hemimegalencephaly, microlissencephaly/microcephaly with simplified gyral pattern, cortical dysplasia
Malformations secondary to abnormal neuronal migration
Malformations secondary to abnormal neuronal migration are a diverse group of malformations in which the movement of neurons from the germinal zone to the cerebral cortex is disturbed. Normally, neurons generated in the walls of the lateral ventricles migrate away from the ventricular surface in a pathway perpendicular to the wall of the ventricle. Because the distance to the neocortex is long compared with the size of the cell, special migration mechanisms have evolved to aid in the migration.
Malformations secondary to abnormal late migration and organization
The last group of disorders to be discussed includes malformations believed to result from developmental abnormalities that occur or are expressed either at the time the neurons reach the cortex or after they reach the cortex and start to establish local and remote synapses. By far the most frequent malformation in this group that is readily identified by imaging is polymicrogyria. Because polymicrogyria has many similarities to schizencephaly, and because the two malformations are commonly
Summary
Malformations of cortical development are an important cause of developmental delay and epilepsy. Proper identification of these malformations can greatly help in accurately counseling affected families and, in some cases, in the treatment of the epilepsy. Modern neuroimaging is an important tool in the diagnosis of these malformations.
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This article is adapted from Barkovich AJ, Raybaud CA. Neuroimaging in disorders of cortical development. Neuroimag Clin N Am 2004;14:231–54.