(A–I) Coronal images of control and HPE brains from anterior (A, D, and G) to posterior (C, F, and I). (A–C) In the control brain, the two hemispheres are separated completely (arrow in A) and the septum (arrow in B) and the corpus callosum (arrowhead in B) are present. (D–F) In alobar HPE, a single cerebral ventricle is present and the interhemispheric fissure is completely absent. (G–I) In semilobar HPE, the two hemispheres are incompletely separated (arrow in G) and the septum and corpus callosum are absent (arrow and arrowhead in H, respectively). (J and K) Horizontal images of control (J) and lobar HPE (K). The septum is present in the control brain (arrow in J); however, it is partially absent in the lobar HPE brain (arrow in K). (L) Sagittal image of a MIH brain. The genu and splenium of the corpus callosum are present (arrows in L); however, the corpus callosum is absent at the region lacking the interhemispheric fissure (arrowhead in L). (M–O) Craniofacial defects associated with HPE. (M) Alobar HPE with cyclopia and proboscis. (N) Semilobar HPE with microcephaly and cleft lip and palate. (O) Semilobar HPE with ocular hypotelorism and midface hypoplasia. (P and Q) Microforms of HPE. (P) Absence of nasal bones and cartilage with a narrow nasal bridge. (Q) Single central maxillary incisor. (R) MIH patient with normal facial appearance. A–C and G–I are reprinted with permission from Cerebral cortex (17); D–F are reprinted with permission from American Journal of Medical Genetics (18); J is reprinted with permission from Brain Maps (111); K is reprinted with permission from MedPix (112); L is reprinted with permission from American Journal of Neuroradiology (23); M and O are reprinted with permission from Human Molecular Genetics (19); N and P are reprinted with permission from Human Molecular Genetics (20); Q is reprinted with permission from Nature Genetics (21); and R is reprinted with permission from Human Molecular Genetics (24).