Rationale: Cortical dysplasia (CD) designates a diverse group of malformati
ons resulting from one or more abnormalities in the development of the cere
bral cortex. The clinical manifestations of CD are varied, probably dependi
ng on the type, location and extent of CD. Epilepsy is a potential late man
ifestation of any cortical malformation. To our knowledge, however, no stud
y has focused specifically on late onset of epilepsy in patients with local
ized CD. Material and Methods: We studied patients with localized CD confir
med by MRI. Patients were divided into 2 groups according to age at onset o
f epilepsy. Group 1 included patients in whom the first seizure occurred up
to the age of 12 (early-onset group) and group 2 included patients in whom
the first seizure occurred after the age of 12 (late-onset group). The two
groups were compared with regard to the type of CD, clinical findings and
EEG findings. Results: Thirty-three patients with various forms of CD were
studied. Onset of epilepsy occurred in adolescence or adulthood in 9 cases
(37%). In 6 of these (17% overall), the first seizure occurred in adulthood
. CD were posterior bilateral pachygyria (1), unilateral polymicrogyria (3)
, focal dysplasia with subcortical gray matter heterotopia (1), perisylvian
bilateral polymicrogyria (1), bioccipital polymicrogyria (1) and bilateral
nodular periventricular gray matter heterotopia (2). The incidence of neur
ological signs was lower in the late-onset group. Mental retardation was mo
derate or absent, thus allowing a fairly normal lifestyle. All patients pre
sented partial seizures with a lower incidence of drug resistance (p < 0.01
). EEG demonstrated preservation of background activity and absence of diff
use or multifocal abnormalities. Conclusion: Onset of epilepsy with various
forms of CD may be delayed until adolescence or adulthood. Prognosis of ep
ilepsy is usually more favorable in these cases.