June 15, 2023
A 24-year-old woman with right frontal focal epilepsy since the age of 12 (clinical and EEG compatible), presents with recent increased seizure frequency (5–8 episodes daily).
Focal Cortical Dysplasia Type II
Background:
- Focal cortical dysplasia (FCD) represents a heterogeneous group of disorders of cortical formation and is one of the most common causes of epilepsy.
- The Blümcke classification system, the most recent globally accepted classification system, divides FCD into 3 types.
- FCD type II is characterized by cortical disorganization plus abnormal dysmorphic or cytomegalic neurons, with or without balloon cells.
Clinical Presentation:
- Typically presents in the pediatric population as a frequent cause of refractory extratemporal epilepsy.
- Prevalence ranges between 5% and 25% among focal epilepsy cases, depending on patient collective and imaging techniques.
Key Diagnostic Features:
- There is overlap of MR imaging features between the different types of FCD and sometimes no abnormality or only a subtle abnormality is evident. In these cases, multimodal neuroimaging is important for the diagnosis (eg. PET, SPECT, magnetoencephalopgraphy), with coregistration assuming a fundamental role in improving detection of FCD. Invasive electroencephalography (icEEG/SEEG) still remains the reference standard in these difficult-to-diagnose cases.
- MRI typical characteristics of FCD type II include:
- commonly located in the frontal lobes
- abnormal gyri and sulci, cortical thickening, and marked blurring of gray/white matter junction
- moderately ↑T2/FLAIR signal and ↓T1 signal of white matter (focal signal abnormality may extend from cortex to ventricle: transmantle sign)
- ↑T2/FLAIR signal of cortical gray matter (despite the cortex remaining hypointense to adjacent white matter)
- FDG-PET: epileptogenic zone is characterized by hypermetabolism during the ictal period (rarely performed) and hypometabolism during interictal period (clinical practice)
- isolated interpretation of FDG-PET results is difficult, necessitating coregistration onto structural MRI
Differential Diagnoses:
- Other typical epileptogenic pathologies in extratemporal topography, eg, developmental abnormalities (heterotopia, polymicrogyria, hemimegalencephaly), epileptogenic tumors (DNET, ganglioglioma, pleomorphic xanthoastrocytoma, MVNT), neurocutaneous syndromes (Sturge-Weber disease or tuberous sclerosis), and miscellaneous lesions (Rasmussen encephalitis, cavernous hemangioma)
Treatment:
- Surgical resection of the refractory epileptogenic area of FCD typically leads to a long seizure-free follow-up period.
