Developmental outcome after surgery in focal cortical dysplasia patients with early-onset epilepsy.

•58.8% of focal cortical dysplasia patents with early epilepsy onset became seizure free after surgery.•76.4% of the patients had stable DQ-IQ and 5.9% had improved DQ-IQ after surgery.•Residual seizures after surgery and lower DQ-IQ before surgery were risk factors for the poor development.•In patients with spasms before surgery, rate of increase in mental age (RIMA) tended to be low after surgery.•In patients with Engel's class I and lower presurgical DQ-IQ, increase of RIMA appeared from two years after surgery.