Abstracts

Malformations of cortical development are a common cause of epilepsy. Focal cortical dysplasia (FCD) and periventricular nodular heterotopia (PNH) may occur either alone or together in the same patient. When together, both lesions are typically bilateral and diffuse but can also occur unilaterally. The presence of PNH with FCD in the immediately overlying cortex suggests an early clonal phenomenon affecting neuronal migration and organization in that region. We report two boys with a large unilateral FCD and PNH in the contralateral hemisphere. This asymmetric distribution of cortical malformation in both hemispheres has not been previously reported and represents a distinct pattern. We identified two patients with focal-onset epilepsy at Children[rsquo]s Hospital Boston. Evaluation included 1.5 Tesla MRI with sagittal T1-weighted images, axial FLAIR and FSE T2-weighted images, and coronal high-resolution SPGR and FSEIR T2-weighted images. Patient 1, an 18-year-old right-handed boy, had mild mental retardation and focal seizures since age 14 years. EEG revealed seizure onset in the right frontal region. MRI revealed a large dysplastic right frontal lobe and a single left-sided PNH adjacent to the left frontal horn. Patient 2, a 10-year-old left-handed boy, had focal seizures since age 6 years. Interictal EEG revealed bilateral intermittent posterior slowing (left greater than right), without epileptiform activity. MRI revealed a large dysplasia involving the entire left temporal, parietal, and occipital lobes, and three foci of PNH on the right side.
In both, the areas of cortical malformation were grossly deformed and involved entire lobes; there was no obvious pachygyria or polymicrogyria; the pattern was clearly distinct from a tuber; and the regions of PNH were contralateral to the large malformations. The novel pattern highlighted in these two children with epilepsy is unilateral FCD with contralateral PNH. We hypothesize that a combination of diffuse and local mechanisms, operating at different times during development, would be necessary to produce this asymmetric pattern. The strikingly asymmetric involvement of the two hemispheres suggests that the stage at which there is disruption of cortical development may differ between the hemispheres and that processes associated with lateralization or regional lobar differentiation may be involved. Further study into the basic mechanisms underlying such patterns of cortical malformation may ultimately enhance our understanding of cortical development, specifically lateralization, in the human brain.