Malformations of Cortical Development: MRI Patterns and Genetic Clues

A practical radiology review of Malformations of Cortical Development: MRI Patterns and Genetic Clues, focused on imaging findings, differential diagnosis, reporting points, and high-yield teaching pearls.

Definition

• ︎Structural brain anomalies disrupting normal cortical formation
• 》Caused by genetic, infectious, or environmental insults
• 》Present with epilepsy, developmental delay, cognitive and neurologic deficits

Classification (New Consensus 2024)

1. Abnormal Cell Proliferation/Apoptosis

• ↓Proliferation → Microcephaly
• ↑Proliferation → Megalencephaly / Hemimegalencephaly
• Focal Cortical Dysplasia (FCD) types IIa–IIb

2. Abnormal Neuronal Migration

• Heterotopia (periventricular, subcortical)
• Lissencephaly (agyria, pachygyria, SBH “double cortex”)
• PMG & Cobblestone malformation (overmigration spectrum)
• Schizencephaly (gray matter–lined cleft)

3. Abnormal Postmigrational Development

• Dysgyria (aberrant gyral pattern, normal thickness)
• FCD types I & III
• Secondary microcephaly

Imaging Pearls

• MRI = gold standard (preferably 3 T)
• Evaluate cortical surface, gyration, cortical thickness, gray–white junction clarity
• Timing of myelination affects lesion visibility
• FCD IIb “transmantle sign”
• PMG irregular bumpy cortex
• Cobblestone thick “pebbled” cortex + ventriculomegaly
• LIS thick smooth cortex, figure-8 brain
• Schizencephaly cleft lined by gray matter (open vs closed lips)

Genetic Highlights

• Microcephaly → ASPM, WDR62, NDE1
• Megalencephaly → PI3K–AKT–mTOR, RAS–MAPK–ERK pathways
• FCD II → mTORopathies (TSC1/TSC2, AKT3, PIK3CA)
• LIS → LIS1, DCX, ARX, RELN, TUBA1A
• Cobblestone → Dystroglycanopathies (POMT1/2, FKRP, FKTN)

Key Differentials

• PVNH vs TSC nodules: only TSC nodules calcify/enhance
• Macrocephaly ≠ Megalencephaly
• LIS vs Cobblestone → under- vs over-migration

Takeaway

MRI pattern recognition + genetic correlation = cornerstone for diagnosis & targeted testing.

MCD classification now emphasizes developmental continuum rather than rigid stage separation.

Reporting focus

State whether the abnormality is focal, multifocal, or diffuse; name the involved lobes and surfaces; and describe cortical thickness, gyration, the gray–white junction, associated white-matter signal, and ventricular configuration. Record accompanying callosal, hippocampal, posterior fossa, or vascular abnormalities. When the appearance is not specific, describe the dominant morphology and provide a short pattern-based differential rather than assigning a genetic diagnosis from MRI alone.