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Polymicrogyria


KEY FACTS

Terminology

  • Malformation due to abnormality in late neuronal migration and cortical organization

    • Neurons reach cortex but distribute abnormally, forming multiple small, undulating gyri

    • Result is cortex containing multiple small sulci that often appear fused on gross pathology and imaging

Imaging

  • Excessively small and prominent convolutions

  • Predilection for perisylvian regions; when bilateral, often syndromic

  • Small irregular gyri, but cortex appears normal or thick on MR

  • May appear as deep infolding of thick cortex

  • MR comprehensively assesses malformation; NECT for suspected Ca++ (TORCH)

Top Differential Diagnoses

  • Microcephaly with simplified gyral pattern

  • Hemimegalencephaly

  • Congenital cytomegalovirus

  • Pachygyria

  • “Cobblestone” malformations

Clinical Issues

  • Polymicrogyria most commonly → developmental delay, seizure

  • Onset and severity of seizures, neurological deficits relate to extent of malformation, presence of associated anomalies

Diagnostic Checklist

  • Remember that polymicrogyria can result from injury, infection, or metabolic or destructive causes

  • If visual or auditory symptoms, rule out congenital infection

Coronal oblique graphic shows the thickened pebbly gyri of polymicrogyria involving the frontal
and temporal
opercula. Note the abnormal sulcation and the irregular cortical-white matter junction
in the affected regions.

Axial T2WI MR of a patient with bilateral perisylvian polymicrogyria shows a thickened, irregular cortex in the insulae
, as well as frontal and parietal opercula
. Incidental cavum septi pellucidi is also seen.

Coronal T1WI MR of the same patient shows thickened, deeply undulating insulae
and opercula around the abnormal sylvian fissures. Polymicrogyria is often more poorly characterized in the coronal plane. The microgyri are not as well seen.

Sagittal T1WI MR shows the characteristic continuation of the perisylvian polymicrogyria posteriorly into the superior parietal lobule
, which establishes the diagnosis. Other abnormal horizontal sulci with thick, irregular cortex
are present.

TERMINOLOGY

Abbreviations

  • Polymicrogyria (PMG)

Definitions

  • PMG: Heterogeneous disorder with “too many/too small” cortical gyri

    • Pathologically, clinically, radiologically, etiologically heterogeneous

  • Malformation due to abnormality in both early (impaired proliferation, migration of neuroblasts) and late (disordered postmigrational cortical maturation) neuronal migration and cortical organization

    • Neurons reach cortex, but distribute abnormally, forming multiple small undulating gyri

    • Result is cortex containing multiple small sulci with fusion of molecular layer (layer 1) of cortex

      • –

        May give false impression of several large, thick gyri

IMAGING

General Features

  • Best diagnostic clue

    • Excessively small gyri and prominent convolutions

  • Location

    • Can be unilateral, bilateral, multifocal

    • Predilection for perisylvian regions

    • When bilateral, often symmetric

  • Size

    • Ranges from single gyrus to entire cerebrum

  • Morphology

    • Small irregular gyri, but cortex looks normal or thick

    • May appear as deep infolding of thick cortex

CT Findings

  • NECT

    • Look for altered sulcation pattern; suggests PMG

    • Excessive small convolutions difficult to detect on CT due to poor contrast resolution

    • Will detect periventricular Ca++ if secondary to cytomegalovirus (CMV)

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