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Polymicrogyria

Summary

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  • Polymicrogyria is a malformation of cortical development characterised by excessive small gyri and shallow sulci
  • Results from abnormal neuronal migration and organization during fetal brain development
  • Imaging shows thickened cortex with irregular gray-white matter junction and multiple small gyri

Pathophysiology

  • Occurs due to disruption of late neuronal migration or early cortical organization (weeks 16-24 of gestation)
  • Proposed mechanisms:
    • Genetic mutations (e.g., GPR56, TUBB2B, PAX6)
    • Intrauterine infections (e.g., cytomegalovirus, toxoplasmosis)
    • Ischaemic insults during fetal development
  • Results in abnormal cortical lamination and excessive small gyri formation

Demographics

  • Prevalence estimated at 1 in 2500 live births
  • No significant gender predilection
  • Can occur in isolation or as part of genetic syndromes (e.g., 22q11.2 deletion syndrome)

Diagnosis

  • Clinical presentation varies widely:
    • Seizures (most common manifestation)
    • Developmental delay
    • Motor deficits
    • Cognitive impairment
  • Diagnosis primarily based on neuroimaging findings
  • Genetic testing may be indicated in some cases

Imaging

  • MRI is the modality of choice:
    • T1-weighted images: Thickened cortex with irregular gray-white matter junction
    • T2-weighted images: Multiple small gyri creating a "bumpy" cortical surface
    • FLAIR: May show subcortical and deep white matter signal abnormalities
  • Patterns of involvement:
    • Focal: Affects a single lobe or region
    • Multifocal: Multiple non-contiguous areas
    • Diffuse: Bilateral and extensive involvement
  • Common locations:
    • Perisylvian region (most frequent)
    • Frontal lobes
    • Parietal lobes
  • Associated findings:
    • Ventriculomegaly
    • Corpus callosum abnormalities
    • Cerebellar dysplasia

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  • 25-year-old patient with lifelong seizures.
  • The cortex lining the right intraparietal sulcus was thickened and irregular.

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  • A 50-year-old patient with a hemiplegia since birth presented with a possible seizure.
  • MRI showed extensive polymicrogyria over the right cerebral hemisphere.

Treatment

  • No curative treatment available
  • Management focuses on symptom control:
    • Antiepileptic drugs for seizure control
    • Physical therapy for motor deficits
    • Occupational and speech therapy for developmental delays
  • Surgical interventions:
    • Focal resection for intractable epilepsy in select cases
    • Hemispherectomy for extensive unilateral involvement
  • Genetic counseling for familial cases
  • Regular follow-up to monitor developmental progress and manage complications

Differential diagnosis

Differential Diagnosis Distinguishing Feature
Lissencephaly Smooth brain surface without excessive gyri; polymicrogyria has numerous small gyri
Pachygyria Broad, thick gyri; polymicrogyria has small, numerous gyri
Schizencephaly Clefts extending from cortical surface to ventricles; not present in polymicrogyria
Focal cortical dysplasia Focal cortical thickening and blurring of gray-white matter junction; polymicrogyria has more diffuse cortical involvement
Ulegyria Mushroom-shaped gyri with preferential involvement of depths of sulci; polymicrogyria affects entire gyri
Perinatal hypoxic-ischaemic injury Often bilateral and symmetric; polymicrogyria can be unilateral or asymmetric
Congenital cytomegalovirus infection Periventricular calcifications often present; not typically seen in polymicrogyria
Tuberous sclerosis Cortical/subcortical tubers and subependymal nodules; absent in polymicrogyria
Zika virus infection Subcortical calcifications and ventriculomegaly; not typical features of polymicrogyria