POLYMICROGYRIA

OVERVIEW

Polymicrogyria is a common malformation of cortical development, where there is abnormal layering, excessive gyration (folding), and gyral fusion in the cerebral cortex. Polymicrogyria may be bilateral, or less commonly unilateral. It occurs most frequently in the perisylvian cortex (80%) and can result in the Sylvian fissure having an abnormal extension and orientation. Polymicrogyria can co-occur with other structural abnormalities, including abnormalities of the white matter, corpus callosum, cerebellum and basal ganglia.

Clinical Context

The clinical presentation of polymicrogyria depends on the extent of the malformation, and whether the malformation is unilateral or bilateral. It also depends on whether there are other brain structural abnormalities. Developmental, cognitive and motor impairments can occur. Unilateral polymicrogyria can be associated with contralateral hemiparesis. Impairments are more significant in those with bilateral or extensive polymicrogyria. Seizures onset occurs within the first year in ~ 50%, and within the first 5 years in ~70%, but seizures may not start until the second decade of life.

Causes of polymicrogyria:

• Gene abnormalities e.g. WDR62 and PIK3R2
• Intrauterine cerebral injury, after approximately 20 weeks gestation, e.g. infection such as CMV, or hypoxia-ischemia
• Metabolic etiology e.g. peroxisomal disorders

Bilateral perisylvian syndrome

Bilateral perisylvian polymicrogyria can cause facial and oromotor dysfunction, resulting in difficulty with tongue, facial and pharyngeal movement. Patients have difficulty with feeding, swallowing and speech. Speech can be limited, and patients may require communication aids. The jaw jerk is brisk and the gag reflex may be absent. Motor impairment in the limbs can be mild. Cognitive impairment may be mild to moderate.

Aicardi syndrome

A genetic syndrome, that manifests in females, and is presumably X-linked with:

• Malformation of cortical development, most commonly polymicrogyria, and grey matter heterotopia, this may be unilateral or bilateral
• Agenesis/dysgenesis of the corpus callosum
• Choroid plexus cysts, with risk of papilloma
• Retinal/eye abnormality - may have chorioretinal lacunae, microophthalmia, coloboma - if the malformation of cortical development is unilateral, the eye findings may be unilateral/ipsilateral
• Skeletal abnormality - affecting the spine and ribs, that may result in scoliosis
• Facial features that may include a short philtrum, a flat nose with upturned tip, large ears and sparse eyebrows