<aside>
Polymicrogyria (PMG) is a cortical malformation characterized by an excessive number of abnormally small gyri with abnormal cortical lamination. It is due to disruption of late neuronal migration and early cortical organization (after 24 weeks of gestation).
</aside>
Causes:
| Category | Examples |
|---|---|
| Genetic | Mutations in SRPX2, TUBB2B, GPR56, PAX6 |
| Infectious | ‣, ‣ |
| Ischemic | Perinatal hypoxia-ischemia, ‣ |
| Metabolic | Congenital disorders of glycosylation |
| Unknown/idiopathic | Common |
| Symptom | Notes |
|---|---|
| Epilepsy | Common; often drug-resistant |
| Developmental delay | Especially in bilateral or extensive PMG |
| Intellectual disability | Variable severity |
| Motor deficits | Spasticity, hypotonia, or diplegia (esp. perisylvian PMG) |
| Oromotor dysfunction | In bilateral perisylvian PMG – drooling, dysphagia, dysarthria |
Subclassification by distribution:
| Type | Features |
|---|---|
| Focal PMG | Unilateral, confined to one lobe; often frontal |
| Multifocal PMG | Multiple lobes, asymmetrically involved |
| Bilateral symmetric PMG | Often perisylvian; strongly associated with genetic or infectious causes |
| Generalized PMG | Severe, often with early-onset epilepsy and global delay |
Syndromic Associations
| Syndrome | Features |
|---|---|
| Bilateral perisylvian syndrome (BPP) | Bilateral PMG around sylvian fissures, pseudobulbar palsy, cognitive delay |
| Aicardi syndrome | PMG, agenesis of corpus callosum, infantile spasms |
| Congenital CMV syndrome | PMG with calcifications, ventriculomegaly, microcephaly |
| Zika virus | PMG, cortical thinning, ventriculomegaly, calcifications |
<aside>
PMG appears as thickened, irregular cortex with excessive small gyri and indistinct white–gray matter junction on MRI, best appreciated on high-resolution coronal images.
</aside>
MR findings
| Feature | Description |
|---|---|
| Excessive small gyri | Thin and irregular; best seen on T1 and T2 coronal views |
| Thickened cortex | Irregular cortical–white matter junction |
| “Bumpy” or “pebbled” surface | Key visual hallmark of PMG |
| Grey matter–white matter blurring | Due to disorganized cortical layering |
| Sulcation | Shallower and more numerous than normal; may give a “cobblestone” appearance |
Axial MRI images at 7 T showing different morphological aspects of polymicrogyria in five young adult patients: (A) Pebbled aspects of grey matter typical of polymicrogyria, with areas of thickening and infoldings, affecting the posterior frontal and parietal cortex on both sides, in a young woman (inversion recovery weighed). (B) Images from the same patient taken with use of susceptibility weighed sequences, with details of the cortex at the parietal-lobe level, showing the underlying structure of the malformed cortex, which is thin and overfolded with ribbon-like aspect. The arrows show the areas where these characteristics are more prominent. The cortex has normal thickness and shape in the mesial hemispheric surface. (C) Gross thickening and abnormal sulcation of the posterior perisylvian and parietal cortex of the left hemisphere in a young man (T1 weighted). (D) Images from the same patient taken with use of susceptibility weighed sequences, showing ribbon-like cortical overfolding bordering the abnormal sulci. The cortex in the contralateral hemisphere is normal. (E) Images from the same patient as in figure 1N, taken with use of susceptibility weighed sequences. The abnormally thick and overfolded cortex in the perisylvian borders (arrows) abruptly transitions to the normal temporo-parietal cortex (black asterisks). (F) Abnormal infolding due to abnormal sulcation and cortical thickness in a young man with left unilateral perisylvian polymicrogyria (susceptibility weighed). (G) An extensive area of heterotopia affecting most of the right frontal lobe in a young man (inversion recovery weighed). The macronodular aspect of the heterotopia and the irregular surface of the overlying cortex (black asterisk) make this malformation not easily distinguishable from, for example, the left parietal lobe in patients in parts A and C. (H) A detail from part G with tissue border enhancement (inversion recovery acquisition technique), which helped to define the border between grey and white matter to diagnose this malformation as heterotopia, although the overlying cortex contained small gyri and abnormal sulci.
Guerrini R, Dobyns WB. Malformations of cortical development: clinical features and genetic causes. The Lancet Neurology. 2014;13(7):710-726. doi:https://doi.org/10.1016/s1474-4422(14)70040-7