One of the most common malformations of cortical development.  

Bilateral perisylvian polymicrogyria (BPP) is the most common subtype , causes the congenital bilateral perisylvian syndrome:

• oromotor dysfunction,
• cognitive impairment,
• epilepsy.

Many possible causes eg vascular or hypoxaemic insults (eg twin-to-twin transfusion syndrome) and congenital cytomegalovirus infection. Genetic causes also important – some syndromes eg 1p36.3 and 22q11.2 deletion syndromes. PIK3R2  gene defects are the most common genetic cause of BPP in patients with normal head size, and the second (to  PIK3CA ) most common cause of polymicrogyria associated with large head size. RTTN gene  also associated with isolated BPP.

[Lancet Neurology, The, 2015-12-01, Volume 14, Issue 12, Pages 1182-1195]