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Focal Cortical Dysplasia (FCD)

Summary

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  • Focal cortical dysplasia is a congenital malformation of cortical development characterised by abnormal neuronal migration, proliferation, and organisation.
  • It is a common cause of drug-resistant epilepsy in children and young adults.
  • Imaging findings include cortical thickening, blurring of the grey-white matter junction, and transmantle sign on MRI.

Pathophysiology

  • FCDs result from disruptions in normal cortical development during embryogenesis
  • Classified into three main types based on histopathological features:
    • Type I: Abnormal cortical layering
    • Type II: Dysmorphic neurons and balloon cells
    • Type III: Associated with other lesions (e.g., hippocampal sclerosis, tumours)
  • Genetic mutations, particularly in mTOR pathway genes, have been implicated in some FCD cases

Demographics

  • Most common cause of focal epilepsy in children and second most common cause in adults
  • Prevalence estimated at 1 in 2,500-5,000 individuals
  • No significant gender predilection
  • Can occur at any age, but typically presents in childhood or early adulthood

Diagnosis

  • Clinical presentation:
    • Focal seizures, often drug-resistant
    • Developmental delay or cognitive impairment in some cases
  • EEG:
    • Focal epileptiform discharges
    • Localised slow activity
  • Neuroimaging:
    • MRI is the gold standard for diagnosis
    • CT may be normal or show subtle cortical abnormalities
  • Histopathological examination of resected tissue for definitive diagnosis

Imaging

  • MRI findings:
    • Cortical thickening
    • Blurring of the grey-white matter junction
    • Transmantle sign (subcortical white matter signal abnormality extending from cortex to ventricle)
    • T2/FLAIR hyperintensity in the affected cortex and subcortical white matter
    • Abnormal gyral/sulcal patterns
  • Advanced MRI techniques:
    • Diffusion tensor imaging (DTI): Altered white matter tract organisation
    • MR spectroscopy: Reduced N-acetylaspartate (NAA) and increased myoinositol
  • PET:
    • Focal hypometabolism in the affected area
  • SPECT:
    • Ictal hyperperfusion and interictal hypoperfusion

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  • 30-year-old patient with frontal lobe seizures.
  • MRI showed a subtle region of cortical thickening at the depth of the inferior frontal sulcus.
  • A hyperintense tail extending towards the lateral ventricle indicated a Type II focal cortical dysplasia.

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  • 25-year-old male presenting with left hand sensory aura.
  • MRI showed thickened cortex of the long gyri of the right insula (red arrow) consistent with a focal cortical displasia.

panels-1 * A 30-year-old patient with epilepsy since childhood. * MRI showed cortical thickening and subcortical T2-hyperintensity that was consistent with a FCD.

panels-1 * A 20 year presented with a left posterior frontal seizure focus based on EEG and clinical presentation. * MRI showed a juxtacortical rim of high signal on T2-weighted imaging and blurring of the grey-white matter interface on T1-weighted imaging.

Treatment

  • Medical management:
    • Anti-epileptic drugs (AEDs) as first-line treatment
    • Often refractory to multiple AEDs
  • Surgical management:
    • Resection of the dysplastic cortex is the definitive treatment for drug-resistant epilepsy
    • Tailored resection based on electroclinical data and imaging findings
    • Invasive EEG monitoring may be required for precise localisation
  • Alternative treatments:
    • Vagus nerve stimulation
    • Responsive neurostimulation
    • Ketogenic diet
  • Post-surgical outcomes:
    • Seizure freedom rates vary from 50-80% depending on the extent of resection and FCD type
    • Better outcomes associated with complete resection of the lesion

Differential diagnosis

Differential Diagnosis Differentiating Feature
Low-grade glioma FCD typically has blurring of gray-white matter junction; gliomas often have more distinct borders
Tuberous sclerosis Tuberous sclerosis usually has multiple cortical tubers; FCD is typically a solitary lesion
Polymicrogyria Polymicrogyria shows excessive cortical folding; FCD often has a thickened cortex
Hemimegalencephaly Hemimegalencephaly affects an entire hemisphere; FCD is usually focal
Ganglioglioma Gangliogliomas often have cystic components; FCD is typically solid
Dysembryoplastic neuroepithelial tumour (DNET) DNETs often have a "bubbly" appearance on MRI; FCD typically appears as cortical thickening
Encephalitis Encephalitis often shows diffuse involvement and oedema; FCD is a stable, focal lesion
Cortical infarct Infarcts follow vascular territories; FCD does not respect vascular boundaries
Rasmussen's encephalitis Rasmussen's shows progressive hemispheric atrophy; FCD is non-progressive
Sturge-Weber syndrome Sturge-Weber has leptomeningeal angiomatosis; FCD does not involve meninges 
    * A 20 year presented with a left posterior frontal seizure focus based on EEG and clinical presentation.
    * MRI showed a juxtacortical rim of high signal on T2-weighted imaging and blurring of the grey-white matter interface on T1-weighted imaging.