Pachygyria with cortical thickness between 5 and 10 mm with and a posterior predominant severity gradient. The severity gradient is determined based on the gyral width, with gyri typically over 5mm over the more severely affected regions. Posterior predominant gradient indicates pachygyria more severe other the occipital lobes but also includes a rare perisylvian-predominant pachygyria and a temporal predominant pachygyria. [from HPO]