Focal cortical dysplasia

Focal cortical dysplasiadysplasias isrepresent a heterogeneous group of disorders of cortical formation, which may demonstrate both architectural and proliferative features. They are one of the most common causes of epilepsy and can be associated with hippocampal sclerosis and cortical glioneuronal neoplasms. 

Clinical presentation

It's a frequent cause of refractory epilepsy. 

Epidemiology

Age of presentation, usually with epilepsy depends to a degree on the type of cortical dysplasia, with type I (see below) more frequently presenting in adulthood ⁴. 

Classification

A number of classification systems for focal cortical dysplasia have been devised over the years since first description in 1971 by Taylor et al ⁵. 

The most common classification used until recently was the a histopathological system proposed by Pamini et al ⁶ in 2004 a genetic / imaging classification by Barkovich et al ² in 2005.

The most recent classification system is that proposed by Blumcke in 2011 and has been widely accepted. 

Unfortunately, as is the case with many classification systems that have developed in parallel with numerous iterations and revisions, there is significant overlap between the various classifications systems with the same terminology used slightly differently. As such it is safest to explicitly state which classification system is being used (e.g. "Blumcke Type IIB"). 

• Taylor dysplasia (1971)
• Palmini classification of focal cortical dysplasia (2004)
• Barkovich classification of focal cortical dysplasia (2005)
• Blumcke classification of focal cortical dysplasia (2011)

Radiographic features

MRI

MRI studies could be negativeis the modality of choice to assess patients with possible focal cortical dysplasias. There is much overlap of imaging features between the different types of FCD, and in many instances no MRI abnormality is evident (especially Blumcke mild MCD). 

General features of focal cortical dysplasia include ⁴: 

cortical thickening, blurring of white matter – gray matter junction with abnormal architecture of subcortical layer, altered signal from white matter with or show signs of:without the penetration through cortex (transmantel sign), altered signal from gray matter, abnormal sulcal or gyral pattern and segmental and/or lobar hypoplasia/atrophy.

• structure
  • focal cortical thickening and
  • abnormal gyration with or without
  • blurred cortex/white matter interface
  • segmental and/or lobar atrophy / hypoplasia
• signal
  • T2/ FLAIR signal hyperintensity of cortex
  • T2/ FLAIR signal hyperintensity of white matter

In addition , each type of focal cortical dysplasia can exhibit more or less of these features. The types below refer to the Blumcke classification of focal cortical dysplasia (2011). 

Type I

• location
  • type Ia - usually confined to temporal lobes 
    • if associated with hippocampal atrophy (as is comon), it is now classified as type IIIa in the Blumcke classification. 
  • type Ib - more frequently seen outside of the temporal lobes
• structure
  • blurring of cortex/whitegrey / white matter interface.junction (less marked than with Type II FCD)
  • prominent segmental or lobar atrophy / hypoplasia with loss of regional white matter volume

  Differential diagnosis

  Imaging differential considerations include:

• signal
  • white matter
    • DNETmoderately increased T2/FLAIR signal 
    • gangliogliomadecreased T1 signal 
    • low grade glioma
  • hamartoma of tuberous sclerosis