Isolated focal cortical dysplasia type II

Isolated focal cortical dysplasia type II (FCD type II) is a rare malformation of cortical development characterized by a localized area of abnormal brain structure resulting from disrupted neuronal migration and organization during fetal development. It is one of the most common causes of drug-resistant (medically refractory) focal epilepsy, particularly in children. FCD type II is subdivided into type IIa, which features dysmorphic neurons without balloon cells, and type IIb, which includes both dysmorphic neurons and balloon cells. The condition primarily affects the cerebral cortex and can occur in any lobe of the brain, though it is most frequently found in the frontal lobe. The hallmark clinical feature of isolated FCD type II is recurrent focal seizures, which often begin in childhood and are typically resistant to antiepileptic medications. Seizure semiology depends on the location of the dysplastic cortex. Patients may also experience developmental delay, cognitive impairment, or neurological deficits depending on the size and location of the lesion. Brain MRI often reveals characteristic findings including cortical thickening, blurring of the gray-white matter junction, and a transmantle sign (a hyperintense signal extending from the cortex to the ventricle on T2/FLAIR sequences), particularly in type IIb. The primary treatment approach involves antiepileptic drug therapy, though many patients with FCD type II have pharmacoresistant epilepsy. Surgical resection of the dysplastic cortex is the most effective treatment and can result in seizure freedom in a significant proportion of patients, especially when complete resection is achieved. Presurgical evaluation typically includes video-EEG monitoring, high-resolution MRI, and sometimes invasive intracranial EEG monitoring to precisely delineate the epileptogenic zone. Recent research has implicated somatic mutations in the mTOR signaling pathway (including MTOR, DEPDC5, TSC1, and TSC2 genes) in the pathogenesis of FCD type II, which has opened potential avenues for targeted therapies such as mTOR inhibitors, though these remain under investigation.

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