Focal cortical dysplasia (FCD) is a variety of congenital (present at birth) abnormalities associated with focal epilepsy. FCD affects the development of the cerebral cortex (top layer of the brain) in both children and adults. When in utero, neurons migrate from the center of the brain in the germinal zones to the outer areas and the neurons do not migrate in the proper formation, areas of focal cortical dysplasia are formed. These areas are highly epileptogenic – meaning that they are likely to produce seizures. Focal cortical dysplasia is a common cause of drug-resistant epilepsy and about 76% of patients with it will not respond to anti-epileptic drugs (AEDs).
How prevalent is FCD?
Focal cortical dysplasia is a congenital abnormality that usually occurs sporadically without any obvious cause. It has not been linked to any medications taken by the mother during pregnancy. In some cases, FCD may be part of a larger genetic abnormality such as Tuberous Sclerosis. FCD is estimated to be present in 1 in 2,500 newborn infants.
How is FCD Detected?
The most common symptom of FCD is focal seizures and focal seizures that secondarily generalize to cause a generalized tonic-clonic seizure. Although focal cortical dysplasia is a congenital malformation and present at birth, the patient may not develop epilepsy until childhood, adolescence, or adulthood. During the investigative work-up to search for a cause of the seizures, brain MRI often reveals the focal cortical dysplasia. The FCD can be subtle on MRI and very difficult to see on CT scans. Prior to high resolution MRI, focal cortical dysplasia was discovered on autopsy and thought to be very rare. With the continuous improvement of MRI and other neuroimaging techniques, recognition and localization of the FCD can be more precise.
What are the Treatments?
The treatment is based on controlling the seizures. Focal seizures with identified focal cortical dysplasia can be very difficult to control with antiepileptic medications. Surgical removal of the FCD and surrounding epileptogenic (seizure-causing) zone may lead to a seizure-free life for the patient. Scalp EEG often shows prolonged or continuous runs of spikes usually localized to the scalp over the dysplastic lesion. Invasive EEG, which records from electrodes placed directly in or on the cortex by a neurosurgeon, is necessary to localize the epileptogenic zone prior to the surgical removal.
Where can I learn more?
An article, “Focal dysplasia of the cerebral cortex in epilepsy” was published in 1971 after lobectomy brain specimens of ten patients with epilepsy were noted as having “unusual microscopic abnormality.” Since then, developments in the recognition, understanding, and treatment of epilepsy caused by focal cortical dysplasia has greatly expanded. The resources below are a great way to learn more.
Taylor DC, Falconer MA, Burton CJ, Corsellis JA. Focal dysplasia of the cerebral cortex in epilepsy. J Neurol Neurosurg Psychiatry 1971:34:369–387