Thick Cortex
Susan I. Blaser, MD, FRCPC
DIFFERENTIAL DIAGNOSIS
Common
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Encephalitis
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Herpes Encephalitis
Less Common
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Hypomyelination (Pseudo Thick Cortex)
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Tuberous Sclerosis Complex
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Taylor Cortical Dysplasia
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Pachygyria-Polymicrogyria
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Hemimegalencephaly
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Lissencephaly Type 1
Rare but Important
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Neoplasms Associated with Cortical
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Dysplasia
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DNET
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Ganglioglioma
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Dysplastic Cerebellar Gangliocytoma
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Glioblastoma Multiforme
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Gliomatosis Cerebri
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Meningioangiomatosis
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Congenital Muscular Dystrophy
ESSENTIAL INFORMATION
Key Differential Diagnosis Issues
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EXCLUDES transient (e.g., MELAS, cortical edema from stroke/seizure, etc.)
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Is cortex thick on both T1 and T2W sequences?
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Does cortex follow gray matter signal intensity (malformations)? or is it hyperintense (infection, neoplasm)?
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Is thickened cortex very focal (think neoplasm)? or more generalized (malformation)?
Helpful Clues for Common Diagnoses
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Encephalitis
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Commonly identified agents: Enterovirus, HSV1, Mycoplasma pneumonia, Epstein-Barr, HHV-6, influenza
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Etiology not found in ≈ 50%
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Hyperintense on T2WI, FLAIR
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Thickened, hyperintense temporal lobe/insular cortex
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Herpes Encephalitis
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Often bilateral, asymmetric
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Look for cingulate gyrus, subfrontal cortex involvement
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Restricts strongly on DWI
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Enhancement, hemorrhage follow
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Helpful Clues for Less Common Diagnoses
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Hypomyelination (Pseudo Thick Cortex)
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Diminished/absent white matter (WM) myelination for age
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Lacks peripheral “arborization” of white matter
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Can be primary or secondary
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Primary hypomyelination (e.g., Pelizaeus-Merzbacher )
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Secondary (prematurity, malnutrition)
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Imaging
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“Pseudo” thick cortex appearance
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Poor gray-white differentiation on T1WI in children > 1 year
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Poor gray-white differentiation on T2WI in children > 2 years
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Small brain with thin corpus callosum
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Tuberous Sclerosis Complex
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Flattened, thickened gyri with “blurred”
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GM/WM border
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Can be calcified, involve entire mantle
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Look for subcortical WM hyperintensities, subependymal nodules
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Taylor Cortical Dysplasia
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Also known as focal cortical dysplasia (FCD) type 2A/B
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“Balloon cell” dysplasia
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Malformation of cortical development
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Refractory focal epilepsy
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Thickened cortex with T1 hyperintensity, T2 hypointensity in infancy
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Rare Ca++
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Lesion conspicuity decreases with WM maturation
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Pachygyria-Polymicrogyria
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Polymicrogyria → excessively small, prominent convolutions (“gyri on gyri”)
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Pachygyria (sometimes called incomplete lissencephaly) → thickened, dysplastic cortex
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Both cause appearance of “thick cortex” on imaging
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Density/signal intensity of affected cortex same as normal gray matter
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Hemimegalencephaly
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Lissencephaly Type 1
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Most severe type (complete agyria) is Miller-Dieker syndrome
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Thick, multilayered cortex
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“Hour glass” configuration with shallow sylvian fissures in severe cases
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Helpful Clues for Rare Diagnoses
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DNET
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Young patient, longstanding seizures
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Well-demarcated “bubbly” intracortical mass
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Often associated with adjacent cortical dysplasia
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Ganglioglioma
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Child/young adult, seizures
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Superficial hemispheres, temporal lobe
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Cyst with nodule, ± Ca++, enhancement typical
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Solid ganglioglioma can resemble Taylor cortical dysplasia (TCD does not enhance)
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Dysplastic Cerebellar Gangliocytoma
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Thickening, overgrowth of cerebellar folia
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Gyriform “layered” or “striated” pattern
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Can cause significant mass effect
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Cowden-Lhermitte-Duclos (COLD) syndrome is considered new phakomatosis
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Multiple hamartoma-neoplasia syndrome
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Long-term cancer screening (breast, thyroid)
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Glioblastoma Multiforme
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White matter > > gray matter
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Tumor infiltration of cortex, subpial extension may occur late
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Hemorrhage, enhancement common
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Primary GBM (older patient) 95% necrotic with thick irregular enhancing rim
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Secondary GBM (younger patient) shows enhancing focus within lower grade tumor
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Gliomatosis Cerebri
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Tumor infiltrates but preserves underlying brain architecture
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2 or more lobes affected
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T2 hyperintense infiltrating mass enlarges cortex, basal ganglia
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MRS shows elevated myoinositol (mI)
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Most are WHO grade II or III diffusely infiltrating astrocytoma
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Meningioangiomatosis
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Cortical mass with variable Ca++
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Linear &/or gyriform enhancement
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Perivascular proliferation of vessels in meninges, cortex
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May infiltrate along perivascular spaces, cause mass effect
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Congenital Muscular Dystrophy
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Cobblestone lissencephaly (overmigration)
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Z-shaped brainstem
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Hypoplastic rotated cerebellum (similar to Dandy-Walker continuum)
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Image Gallery
![]() (Left) Axial NECT in a 4 month old with hypomyelination
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