Abstracts

Development of the human brain occurs in stages that encompass proliferation and differentiation, migration, and cortical organization. These organized stages take place at different moments of the embryonic development. Interruption of this process may result in different types of malformations of cortical development (MCD). It is believed that the type of MCD is stage-related, being determined by the moment of disruption. We describe the neuroimaging findings of a series with MCD and document the association of more than one MCD occuring at different moments of embryogenesis.
MR were reviewed by two neuroradiologists, blinded to clinical details, to determine the imaging features and classify according to the main MCD according to Barkovich et al. MCD were classified as proliferative, migrational and organizational in nature. Clinical information was prospectively collected with a standard questionnaire and by review of hospital records.
Our group consisted of 74 patients with epilepsy determined by MCD, mean age 8 y. 33.8% had a malformation of proliferation or differentiation, 31.1% of migration, and 35.1% of organization. The main malformations were: focal cortical dysplasia(29.7%), polymicrogyria(27%), nodular heterotopia(16.4%), schizencephaly/cleft(8.1%), transmantle dysplasia(5.4%), subcortical band heterotopia(5.4%), hemimegalencephaly(4.1%) and pachygyria/ lissencephaly(4.1%). A total of 42 patients (56.8%) showed one abnormality (cortical or subcortical) other than the most important for classification. A total of 33 (44.6%) patients presented other cerebral malformations including commissural dysgenesis (20.3%); posterior fossa malformation (18.9%, affecting the cerebellum in 12 patients); ventricular dilatation or dysmorphism (14.9%) and white matter alterations (6.8%), excluding the hypersignal observed in FCD. Five of these patients presented associated hipocampal atrophy. Fifteen patients (20.3%) had more than one MCD consistent with defects occurring at more than one developmental stage. From this group, nodular heterotopia was the most frequently (50%) associated with abnormalities in the overlying cortex. Commissural abnormalities occurred in 38.5% of patients with polymicrogyria/schyzencephaly and cerebelar dysgenesis in 16% of patients with nodular heterotopia.
This study illustrates that the spectrum of MCD is not completely well-defined and that many patients may present more than one malformation occurring at different stages of the embrionary process. Since it is highly unlikely that two insults have occurred at two different moments in this expressive number of patients, this process may not be restricted to one specific moment and when the process goes wrong it may affect different stages. It remains to be determined whether a genetic predisposition may underlie a more complex response observed in some of these patients.