Polymicrogyria

Cerebral cortex malformation characterized by an uneven cortical surface and an excessive number of small convolutions (gyri) partly merged and separated by shallow sulci.

They can be classified according to:

- histology

- radiology

- or clinical preseetation: isolated or associated with other brain malformations or a malformative complex.

Histology :

* non laminar polymicrogyria: loss of layering of the cerebral cortex, linked to an early cessation of neuronal migration;

* polymicrogyria in 4 layers, probable consequence of a vascular accident between the 20th and 24th week of gestation.

From the radiological point of view, these two histologic forms give a picture of pseudopachygyry (moderately thickened cortical surface).

X-ray topography:

topography	clinical picture	radiology	genetics
bilateral perisylvian (70 % of cases)	pseudobulbar syndrome with mental retardation (30 %) or epilepsy (30 %)	bilateral perisylvian	heterogeneous; possible chromosomal aberrations
bifrontal	encephalopathy with spastic tetraparesis (50%)	symmetric impairment of frontal poles up to the precentral gyrus	sporadic cases; sometimes consanguinity
bilateral fronto-parietal	severe encephalopathy with cerebellar and oculomotor signs	fronto-parietal and frequent cerebellar atrophy	autosomal recessive (GPR56) or isolated cases
parasagittal parieto-occipital bilateral	partial epilepsy and mental retardation (50 %)	parasagittal area and parieto-occipital mesial cortex	sporadic cases (6q16-q22)
bilateral diffuse	encephalopathy of variable severity with epilepsy (80 %)	diffuse predominantly perisylvian	consanguinity; chromosomal aberrations

Clinical presentations:

1) perisylvian (or bi-opercular) polymicrogyria: due to a circulatory problem during the second trimester of pregnancy, or chromosomal aberrations (familial cases) [1p36.3, 22q11.2 etc];
association of

- mental retardation

- orofacial dyspraxia: slurred speech and dysarthria in minor forms. facial diplegia with dysphagia and drooling in severe forms; sometimes pseudobulbar syndrome

- epilepsy (45-90%) the severity of which is related to the extent of polymicrogyria

2) bifronto-parietal polymicrogyria: related to mutations of the GPR56 gene ;
association of

- epilepsy (90 %)

- disorders of eye-tracking

- mental and motor retardation

- cerebellar signs: ataxia

3) bifrontal, biparieto-occipital or bilaterally generalized polymicrogyria: mental retardation and frequent epilepsy
4) micropolygyria:

- associated with periventricular nodular heterotopias

- present in some polymalformative syndromes: Aicardi, (oculo-cerebro-skin) Delleman, Aarskog, Adams Oliver.

Anesthetic implications:

mental retardation, severe epilepsy, side-effects of antiepileptic treatment.

References :

Quelin C, Poirier K, Bahi-Buisson N.
Les polymicrogyries : des formes isolées aux syndromes polymicrogyriques.
Neurone 2012 ; 17 : 16-22.

Updated: October 2018