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CORTICAL MALFORMATIONS IN SURGICAL RESECTIONS FOR EPILEPSY

Focal cortical dysplasias – nomenclature
Cortical dysplasia refers to a subtype of malformations due to abnormal cortical development
(MCD) where the abnormality is strictly or largely intracortical77. In some instances these lesions,
if localised, are amenable to surgical resection. In the past a variety of different terms has been
used for these abnormalities including ‘Taylor type dysplasia’ (after one of the initial descriptions
of this lesion), ‘cortical dysgenesis’ and ‘microdysgenesis’. A reappraisal of the nomenclature
was proposed by Palmini77, based largely on neuropatholgical features, in order to facilitate better
correlation of neuroimaging, clinical-electrographic data and clinical characteristics of different
lesion types between epilepsy centres. The Palmini system has two main groups: the focal cortical
dysplasias (FCDs) and the mild MCDs. The FCDs were divided into two types: type I
(cytoarchitectural abnormalities without balloon cells or dysmorphic neurones); and type II
(cytoarchitectural abnormalities with abnormal neurones or balloon cells). These types are then
further divided, representing a spectrum of increasing severity of pathological dysplasia. A
revised ILAE classification of cortical dysplasias was published in 2011 which includes an
additional tier of dysplasias (type III) seen in association with a second pathology (including
hippocampal sclerosis, tumours, scars and vascular lesions)78. The rationale was to separate
isolated FCD (type I and II) from these associated dysplasias which are likely to have a different
aetiology (linked with the primary pathology), may represent acquired changes in the developed
cortex rather than developmental lesions, and have different prognosis following resection and
clinical and imaging characteristics.

Incidence of FCD: Based on published series between 2005 and 2011 the relative incidence of
reported isolated FCD types is type Ia (46%), type Ib (19%), type IIa (15%) and type IIb (39%);

Table. ILAE 2011 Classification for cortical dysplasia.