Polymicrogyria

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Neuronal Migration and Organization Abnormalities

General

• Aka: cortical dysplasia

Definition

• Multiple small gyri due to a defect in the normal six-layered lamination of the cortex leading to an abnormal distribution of neurons

Mechanism

• Neuronal organization deficit

• Disturbances (typically between 17 and 25-26 weeks of gestation).
• In the late stages of neuronal migration OR
• In the early stages of cortical organization

• This result in the abnormal development of the deep layer of cerebral cortex which manifests as multiple small gyri separated by small sulci → irregular bumpy cortical surface

Imaging

• Small gyri with shallow sulci.

• May be difficult to diagnose by CT/MRI, and may be confused with pachygyria (T1 lissencephaly)

 

Subtypes

• Diffuse or focal

• Unilateral or bilateral

• Symmetric or asymmetric

Location

• Affect a variable portion of the cortex in one or both hemispheres.

• Most common: Posterior end of the sylvian fissure
• Because of telencephalic flexure

• Sylvian cortex (80%)

• frontal lobes (70%)

• Less common
• parietal, temporal and occipital lobes.

• Can be
• Bilateral (60%) or Unilateral (40%)
• Focal or diffuse
• Symmetric or asymmetric.

Pathology

• Hemispheric surfaces have multiple festoon-like convolutions with four cortical layers only;

• Polymicrogyria may demonstrate an irregular and bumpy surface or may be paradoxically smooth as a result of coalescence of microgyri in the molecular (surface) layer

Aetiology

• Intrauterine ischemia
• In utero vascular occlusion (in association with schizencephaly);

• Intrauterine infection (CMV or toxoplasmosis),

• Metabolic disorders (peroxisomal storage disorders, pyruvate dehydrogenase deficiency),

• Genetic syndromes (Aicardi syndrome, DiGeorge syndrome, and Warburg Micro syndrome).
• Mutation of SRPX2 (bilateral sylvian polymicrogyria)
• PAX6
• TBR2
• GPR56

Presentation

• Seizures (80%)
• Infantile seizures with marked developmental delay (also possibly contralateral hemiplegia).

• Microcephaly

• Hypotonia

• Severe motor and intellectual dysfunction
• depending on the extent of cortical involvement