Understanding Focal Cortical Dysplasia: A Simple Explanation
Focal cortical dysplasia (FCD) is a brain development problem where a small area of the brain's outer layer (cortex) didn't form correctly before birth, causing the brain cells in that spot to be disorganized or abnormal. 1
What Happens in the Brain
Think of the brain's outer layer like a well-organized library with books arranged in neat rows and sections. In FCD, one area of this "library" has books scattered randomly, stacked incorrectly, or even the wrong types of books mixed together. 1
The brain cells in the affected area are:
- Arranged in the wrong pattern (disorganized layers) 1
- Sometimes abnormally shaped or sized (called "dysmorphic neurons") 1
- Occasionally include unusual large cells called "balloon cells" that shouldn't be there 1
Why It Matters
FCD is one of the most common causes of seizures that don't respond to medication, especially in children. 2, 3 The abnormal brain tissue acts like faulty electrical wiring, causing seizures that can be difficult to control with standard epilepsy medications. 2, 4
Key clinical features include:
- Seizures typically starting in childhood, though they can begin as late as age 60 2
- Seizures that don't respond well to anti-seizure medications (50-75% of cases are drug-resistant) 2, 5
- Developmental delays or learning difficulties, especially when seizures start early in life 2
How It's Detected
Brain MRI scans can detect most FCDs, but not all. 1, 3 On imaging, doctors look for:
- Areas where the brain tissue looks thicker or thinner than normal 3
- Blurred boundaries between gray matter (brain cells) and white matter (connections) 1, 3
- Abnormal bright signals on certain MRI sequences 3
Important limitation: Type I FCD is often subtle and may appear normal on MRI, making diagnosis challenging even for experienced radiologists. 1 Type II FCD is usually easier to see on brain scans. 1
What Causes It
FCD results from genetic mutations that occur during brain development, affecting how brain cells grow and organize. 1, 4 These are typically:
- Mutations in genes controlling the mTOR pathway (a cellular growth control system) 1, 4
- "Somatic" mutations, meaning they occur only in brain tissue, not throughout the body 4
- Not usually inherited from parents 4, 5
Treatment Options
Surgery to remove the abnormal brain tissue is the most effective treatment, with 50-65% of patients becoming completely seizure-free after surgery. 2, 6
Treatment approach:
- Anti-seizure medications are tried first, but often don't work well 2, 4
- If two different medications fail to control seizures, surgical evaluation should begin 2
- Complete removal of the abnormal tissue offers the best chance for seizure freedom 3, 6
- Newer medications targeting the mTOR pathway may help in some cases 4
Types of FCD
The International League Against Epilepsy classifies FCD into three main types: 1
- Type I: Subtle changes in brain cell organization, harder to see on scans, often affects small areas 1
- Type II: More obvious abnormalities with abnormal cell types, easier to detect on MRI, better surgical outcomes 1
- Type III: FCD combined with another brain problem (like scarring, tumor, or blood vessel malformation) in the same area 1
Common pitfall: Type I FCD in young children may show opposite signal characteristics on MRI during the first few months of life, potentially appearing as bright areas on T1 images and dark on T2 images, which can be confusing but is actually a helpful diagnostic clue. 1