Case of the Week

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.