PMG macroscopic appearance in MRI and fixed brain. a: MRI; horizontal image. The cortex over the insular and frontal areas is polymicrogyric; irregular with many small, densely-packed folds, while the cortex of the posterior brain (below) is normal. b: Coronal slice through a fixed brain shows small, densely-packed cortical folds over the frontal lobes but the cortex of the basal temporal lobes is spared. The corpus callosum is thin and the ventricles are large. c: Lateral view of a fixed brain; the gyri are coarsely nodular. The naked eye appearance of polymicrogyria can be subtle and requires histological confirmation. d. Section of hemisphere with abnormally festooned cortex with multiple small folds in the Sylvian fissure (between black arrows) (LBCV stain).