Thick Cortex

Susan I. Blaser, MD, FRCPC

DIFFERENTIAL DIAGNOSIS

Common

Encephalitis
Herpes Encephalitis

Less Common

Hypomyelination (Pseudo Thick Cortex)
Tuberous Sclerosis Complex
Taylor Cortical Dysplasia
Pachygyria-Polymicrogyria
Hemimegalencephaly
Lissencephaly Type 1

Rare but Important

Neoplasms Associated with Cortical
- Dysplasia
- DNET
- Ganglioglioma
Dysplastic Cerebellar Gangliocytoma
Glioblastoma Multiforme
Gliomatosis Cerebri
Meningioangiomatosis
Congenital Muscular Dystrophy

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

EXCLUDES transient (e.g., MELAS, cortical edema from stroke/seizure, etc.)
Is cortex thick on both T1 and T2W sequences?
Does cortex follow gray matter signal intensity (malformations)? or is it hyperintense (infection, neoplasm)?
Is thickened cortex very focal (think neoplasm)? or more generalized (malformation)?

Helpful Clues for Common Diagnoses

Encephalitis
- Commonly identified agents: Enterovirus, HSV1, Mycoplasma pneumonia, Epstein-Barr, HHV-6, influenza
- Etiology not found in ≈ 50%
- Hyperintense on T2WI, FLAIR
- Thickened, hyperintense temporal lobe/insular cortex
Herpes Encephalitis
- Often bilateral, asymmetric
- Look for cingulate gyrus, subfrontal cortex involvement
- Restricts strongly on DWI
- Enhancement, hemorrhage follow

Helpful Clues for Less Common Diagnoses

Hypomyelination (Pseudo Thick Cortex)
- Diminished/absent white matter (WM) myelination for age
  - Lacks peripheral “arborization” of white matter
- Can be primary or secondary
  - Primary hypomyelination (e.g., Pelizaeus-Merzbacher )
  - Secondary (prematurity, malnutrition)
- Imaging
  - “Pseudo” thick cortex appearance
  - Poor gray-white differentiation on T1WI in children > 1 year
  - Poor gray-white differentiation on T2WI in children > 2 years
  - Small brain with thin corpus callosum
Tuberous Sclerosis Complex
- Flattened, thickened gyri with “blurred”
- GM/WM border
- Can be calcified, involve entire mantle
- Look for subcortical WM hyperintensities, subependymal nodules
Taylor Cortical Dysplasia
- Also known as focal cortical dysplasia (FCD) type 2A/B
- “Balloon cell” dysplasia
- Malformation of cortical development
- Refractory focal epilepsy
- Thickened cortex with T1 hyperintensity, T2 hypointensity in infancy
  - Rare Ca++
- Lesion conspicuity decreases with WM maturation
Pachygyria-Polymicrogyria
- Polymicrogyria → excessively small, prominent convolutions (“gyri on gyri”)
- Pachygyria (sometimes called incomplete lissencephaly) → thickened, dysplastic cortex
- Both cause appearance of “thick cortex” on imaging
- Density/signal intensity of affected cortex same as normal gray matter
Hemimegalencephaly
- Hamartomatous overgrowth of part/all of a hemisphere
- Enlarged hemisphere with thickened, often dysplastic cortex
- Ipsilateral ventricle often enlarged, abnormally shaped
- White matter often overgrows, is hypermyelinated
Lissencephaly Type 1
- Most severe type (complete agyria) is Miller-Dieker syndrome
- Thick, multilayered cortex
- “Hour glass” configuration with shallow sylvian fissures in severe cases

Helpful Clues for Rare Diagnoses

DNET
- Young patient, longstanding seizures
- Well-demarcated “bubbly” intracortical mass
- Often associated with adjacent cortical dysplasia
Ganglioglioma
- Child/young adult, seizures
- Superficial hemispheres, temporal lobe
- Cyst with nodule, ± Ca++, enhancement typical
- Solid ganglioglioma can resemble Taylor cortical dysplasia (TCD does not enhance)
Dysplastic Cerebellar Gangliocytoma
- Thickening, overgrowth of cerebellar folia
- Gyriform “layered” or “striated” pattern
- Can cause significant mass effect
- Cowden-Lhermitte-Duclos (COLD) syndrome is considered new phakomatosis
  - Multiple hamartoma-neoplasia syndrome
  - Long-term cancer screening (breast, thyroid)
Glioblastoma Multiforme
- White matter > > gray matter
- Tumor infiltration of cortex, subpial extension may occur late
- Hemorrhage, enhancement common
- Primary GBM (older patient) 95% necrotic with thick irregular enhancing rim
- Secondary GBM (younger patient) shows enhancing focus within lower grade tumor
Gliomatosis Cerebri
- Tumor infiltrates but preserves underlying brain architecture
- 2 or more lobes affected
- T2 hyperintense infiltrating mass enlarges cortex, basal ganglia
- MRS shows elevated myoinositol (mI)
- Most are WHO grade II or III diffusely infiltrating astrocytoma
Meningioangiomatosis
- Cortical mass with variable Ca++
- Linear &/or gyriform enhancement
- Perivascular proliferation of vessels in meninges, cortex
- May infiltrate along perivascular spaces, cause mass effect
Congenital Muscular Dystrophy
- Cobblestone lissencephaly (overmigration)
- Z-shaped brainstem
- Hypoplastic rotated cerebellum (similar to Dandy-Walker continuum)

Image Gallery

Coronal FLAIR MR shows subtle, bilateral signal increase and swelling in the hippocampus

, temporal lobe cortex

, and insular cortex

in a child with proven Mycoplasma encephalitis.

Coronal FLAIR MR shows swollen, hyperintense temporal lobe cortex

with relative sparing of the underlying white matter. DWI (not shown) revealed restricted diffusion in the insular cortex & cingulate gyri.

(Left) Axial NECT in a 4 month old with hypomyelination

shows decreased volume and white matter density. The thin arbors of white matter give a false impression that the cortex, especially in the occipital poles, is thickened