Polymicrogyria (PMG) is a malformation of cortical development in which the cerebral cortex forms an excessive number of abnormally small gyri with abnormal cortical organisation. Epilepsy is common, but the clinical picture varies widely.
PMG is not one single pattern
Polymicrogyria can be focal, multifocal or bilateral. It can affect different lobes and may occur alone or with other brain malformations. The distribution strongly influences neurological features.
Causes
PMG can arise from genetic causes, chromosomal abnormalities, congenital infection, vascular disruption and other developmental mechanisms. In many people, no single cause is identified.
Epilepsy
Seizures may begin in childhood or later and can include focal seizures, focal-to-bilateral tonic-clonic seizures and, in more extensive disease, developmental and epileptic encephalopathy patterns.
Speech, movement and development
Depending on location and extent, PMG may be associated with motor impairment, speech and language difficulty, swallowing problems, learning disability or relatively mild neurological effects.
MRI diagnosis
High-quality MRI is central to diagnosis. Dedicated epilepsy MRI protocols and expert neuroradiology can be important because cortical malformations can be subtle.
Drug-resistant epilepsy
Some people respond to antiseizure medicines; others develop drug-resistant epilepsy. Surgical evaluation can be challenging when abnormalities are bilateral or widespread because the MRI lesion may extend beyond the true epileptogenic network.
Epilepsy surgery
A 2026 systematic review found that resective and disconnective surgical approaches can provide meaningful seizure improvement in selected patients with PMG. Outcomes depend on localisation, extent, eloquent cortex and the feasibility of safely treating the epileptogenic network.
Related reading
- Structural and Acquired Epilepsies
- Focal Cortical Dysplasia
- MRI and Neuroimaging in Epilepsy
- Epilepsy Surgery
Additional clinical detail
Perisylvian polymicrogyria can particularly affect speech, swallowing, oromotor control and language. In selected people with extensive or bilateral malformation, specialist presurgical assessment may still be worthwhile when the epileptogenic network can be localised, sometimes using SEEG.
Sources and further reading
- Efficacy of neurosurgical interventions for epilepsy in polymicrogyria: A systematic review. Epilepsia Open. 2026. PMID: 41689720.
Evidence checked: September 2026.