GPR56 mutation and cobblestone cortex. a: GPR56 mutation in fetus of 27 weeks. There are irregular remnants of the original cortical surface (P) buried beneath a band of white matter. Above this the cortical ribbon is festooned beneath greatly thickened and vascular leptomeninges (L). b: Cobblestone malformation, fetus 20 weeks. There is a more obvious linear remnant of the cortical surface (P). Beneath it are clusters of neurones of the original cortical plate abutting the pial surface. Above is a smooth band of ectopic cortical cells mixed with vascular meninges over the brain surface (L). (a and b H&E).