Ischaemia; fetus of 36 weeks following trauma at 24 weeks gestation. a: A cleft, bordered with irregularly festooned cortex, dips into the brain from the surface. The cleft is immediately adjacent to the infarcted middle cerebral artery territory (box) where there is thickening and increased vascularity of the overlying leptomeninges (reticulin). b: Higher power of the pial surface from area within box in (a) showing apparent loss of pial basement membrane, multiple layers of collagen and large blood vessels. Abnormal masses of cells (presumed over-migrated) are seen between these vessels (arrows). c: An area of normal cortex from the same case stained with reticulin to show the pial basement membrane and surface blood vessels. d: Reactive surface overlying infarcted cortex. The pial basement membrane no longer forms a discrete band but is irregular and thickened with focal breaches (arrows). The surface blood vessels are numerous and dilated.