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the outcome following surgery is that 45%, 49%, 65% and 84% of patients with these subtypes,
respectively, become seizure free.

FCD Type II Neuropathology: The macroscopic appearances from an FCD lesion may show a
region of apparent thickening of the grey matter, blurring of the grey-white boundary and the
tissue may appear firmer. The overall size of these lesions varies and can be up to several
centimetres broad involving both sulci and gryri; occasionally discontinuous regions of dysplasia
are noted and in young individuals extensive involvement of the hemisphere may be seen. The
region of dysplasia in some cases is not seen on visual inspection. Histological appearances
confirm architectural abnormalities of the cortex as common to all types of FCD.

An abnormal laminar cortical architecture (dyslamination) is appreciated with indistinct
boundaries between cortical layers compared to normal, which is more readily apparent with
Nissl or NeuN immunostaining. Cortical layer I may often remain relatively cell-free and defined
in the region of dysplasia, but may be broader than normal. The junction between the deep cortical
layers and white matter is often ill-defined. A lack of any radial alignment of neurones compared
to normal cortex may be present in FCD type II whereas in FCD I, particularly in childhood
epilepsy, an exaggeration of columnar arrangement has been reported79,80. Care should obviously
be taken with the interpretation of any cytoarchitectural ‘abnormality’ in regard to normal cortical
regional variations. Abnormalities of the cortical myelo-architecture may be striking features in
FCD and myelin rarefaction in sub-cortical white matter is a common finding.

Profoundly abnormal cortical cell types are present in FCD and define the subtypes. Dysmorphic
neurones have abnormal size, orientation, dendritic processes and cytoskeletal structure. In
Cresyl violet stained sections Nissl appears abnormally clumped and eccentric thickening of
nuclear membranes can be seen. Dysmorphic neurones may be present in any laminar position
and are occasionally seen in isolation in otherwise apparently normal cortex adjacent to the main
lesion, or in groups trailing into the underlying white matter. In some cases dysmorphic neurones
predominate in the pyramidal cell layers (III and V). Abnormal polarity of these neurones ranges