Hippocampal malrotation. (A, C) Normal control hippocampus (stained with Luxol fast blue, and hematoxylin and eosin) and interpretive line diagram. (B, D) Patient hippocampus (immunostained to detect MAP2) and diagram. (B’) Higher magnification of patient’s dentate gyrus showing reduced neuronal population. The patient’s hippocampus, including dentate gyrus (D), CA1-CA3, and subiculum (S) was rotated by ~90 degrees from normal orientation. The temporal horn (T) of the lateral ventricle directly contacted the subiculum in patient but not control brain. The entorhinal cortex (EC), characterized by large neuron clusters in supragranular layers, appeared expanded in the patient brain (small arrows in D). Other abbreviations: P, presubiculum; L, lateral geniculate nucleus; PNH, periventricular nodular heterotopia; TEC, transentorhinal cortex. Large arrows indicate collateral sulcus. Scale bars: (in B) A-D, 750 μm; B’, 75 μm.