FOCAL CORTICAL DYSPLASIA

Dr Ashraf AbdouProfessor of neurology

Neuropsychiatry departmentAlexandria university

Normal Cortical Development1) Proliferation proliferation of neurons in the ventricular zone and glia in

the subventricular zone

2) Migration Migration of postmitotic neurons to the cortical plateHeading for the deepest layers and then for the superfricial

layerBetween the 8th and 24th weeks of gestation

3) Cortical organization : vertical and horizontal organization of neurons within the

cortex and elaboration of axonal and dendritic branch terminal differentiations, apoptosis, synapse elimination,

cortical remodeling

Proliferation and MigrationGerminal matrix adjacent to the lumen of neural

tube (future ventricles) contains stem cells of the neurons and two types of glial cells.

Neuronal precursor cells migrate along specialized cells called radial glial cells, to one of the six layers of cerebral cortex.

Once at adult site – establish synaptic connections with neighbouring neurons & send axons to targets

Generally migrate centrifugally towards brain surface

Timing of Neuroblast migrationCerebrum – neuroblasts – begin by 6 weeks –

last till 34th weeks

Cerebrum – glioblast – migrate till early post natal period

Brainstem – migration of neuroblast complete by 2 months

Cerebellum – continue till 1 year

Formation of sulci & gyri

Migrating neuroblasts necessitate more surface area without increasing volume

Proliferation of Glia

Growth of dendrites & axons

Neuronal Migration Disorders

I. True migration disorders Neurons fail to reach their intended

destination.

1. Lissencephaly (agyria, pachygyria and sub-cortical band heterotopia).

2. Cobble stone complex malformation. 3. Heterotopias.

II. Malformations of cortical organization.

Microscopic abnormality in cortical arrangement.

1. Polymicrogyria. 2. Schizencephaly. 3. Focal cortical dysplasia.

Lissencephaly with sub cortical band heterotopia.

Clinical features

Normal at birth.

Seizures uncommon on 1st day of life.

Seizures at 3-6 months, later infantile spasm and Lennox- gastaut syndrome.

Profound MR .

Early hypotonia, later spastic quadriplegia and opisthotonus.

Subcortical band heterotopia-Double cortex

Sub-cortical, symmetric, circumferential bands of gray matter, separated from cortex by thin band of white matter. “Double cortex” appearance.

Heterotopias

Group of neurons is an inappropriate location – either below or above the cerebral cortex.

Periventricular nodular heterotopia

Sub-ependymal nodular heterotopia

Periventricular laminar heterotopia

FOCAL CORTICAL DYSPLASIA

Focal Cortical dysplasia

èè

Focal Cortical dysplasia with normal cell types

Pure architectural Dysplasia * Abnormal cortical lamination. * Ectopic neurons in white matter.

Present with – Epilepsy / learning disability.

MRI: Lobar / gyral hypoplasia, atrophy of underlying white matter blurring of gray- white border. Increased T2 & decreased T1 signal intensity.

Focal cortical dysplasia with abnormal cell types (balloon cells)

Cytoarchitectural dysplasia

It is clear only with histopathology, not with MRI

IncidenceAutopsy studies 1.7% incidence of FCD in

normal brains.1The incidence was significantly higher

(46.5%) in patients with epilepsyIn surgical treated epilepsy:

In pediatric patients the incidence was 25%

In an adult population: 15%

Cortical dysplasia and epilepsy77 to 90% of patients with

cortical malformations had seizures.

Cortical dysplasia is the most common substrate in pediatric and the second or third most frequent etiology in adult epilepsy surgery patients

Cortical dysplasia and epilepsyEpilepsy typically manifests during the first

decade of life, usually after 2 or 3 years of age

Seizure semiology depends on the anatomic location of the malformation.

Partial

Partial with 2ry generalization

Many patients have more than one seizure type

Focal cortical dysplasiaMRI :

Focal abnormal gyral(cotical) thickening

Blurring of the cortical-white matter junction

Cortical dysplasia; other clinical presentations

Dysplasia involving extratemporal regions demonstrates earlier age at presentation, more severe epilepsy, higher incidence of mental retardation and developmental delay.

Imaging studiesMilder forms of dysplasia may remain

invisible to current imaging techniques. Other studies report MRI detection of cortical abnormalities in 60 to 90% of the patients with FCD.

Characteristic MRI findings include: abnormal gyral patternsshallow sulci increased cortical thicknesspoor gray-white matter differentiationincreased subcortical signal intensity on T2-weighted

imaging

Focal cortical dysplasia

(A1) T1WI : cortical thickening

(A2) Proton-density-WI : blurring of interface between GM and WM

(A3) T2WI : increased signal change

(A4) FLAIR image : increased signal change

Focal Cortical dysplasia

There is :• cortico-subcortical blurring of the left paramedian frontal cortex• streak of high T2 signal extending from the depth of the sulcus to the

ventricular wall.• T1 hyperintensity of the cortex

Coronal T2WI Axial T2WI Axial T1 MPRAGECoronal T1

MPRAGE recon

5-year-old boy with refractory epilepsy. Coronal T2WI imaging done on 1.5 T MR scanner was read as normal.

Imaging done at 3T with 32 channel head coil demonstrates subtle blurring of the gray-white junction in the left frontal lobe with mild T2 prolongation in the underlying white matter. Increased T1

hyperintensity of the left frontal cortex is also noted. Findings consistent with FCD.

Axial T2WI Coronal T1

MPRAGE recon Coronal FLAIR Axial FLAIR

13 month old male with medically refractory focal seizures. Coronal & axial T2WI MRI done at 1.5 T MR scanner was read as normal.

Same patient as above scanned on a 3T MR scanner. Imaging demonstrates cortical thickening and blurring of gray-white junction in the left temporal lobe. Findings

consistent with cortical dysplasia.

Coronal T2WI Coronal T2WI Axial T2WI Coronal T1 MPRAGE recon

Surgical outcome Approximately 33–75% of individuals

becoming seizure-free. [80% of patients became seizure-free after surgical treatment for mTLE related to HS or lesional epilepsy, such as primary brain tumor or vascular malformations]6,20.

Most important factor: complete removal of dysplastic cortex [70% compared with 22% of those with

incomplete resections - 82% compared with 47% with incomplete resections]