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Facial findings in holoprosencephaly (HPE)
A. Alobar HPE with cyclopia and proboscis above the single eye
B. Alobar HPE with cebocephaly and closely spaced eyes
C. Semilobar HPE with microcephaly, premaxillary agenesis, and midline cleft lip and palate
D. Semilobar HPE with closely spaced eyes, midface retrusion, and mild dysmorphism
Gropman & Muenke [2005] Management of Genetic Syndromes. Copyright John Wiley & Sons Limited. Reproduced with permission.

Alobar HPE
A. MRI of alobar holoprosencephaly (HPE), the most severe form of HPE, characterized by an enlarged midline monoventricle (holoventricle, red/thin arrow) with fusion of the frontal lobes and the midline gray matter structures (thalami and basal ganglia, blue/thick arrow). Typically, the corpus callosum and the third ventricle are absent.
B. Facial features seen in the alobar HPE spectrum, characterized by a single eye-like structure (cyclopia, red/thin arrow) and an overriding nose-like structure (proboscis, blue/thick arrow)
Gropman & Muenke [2005] Management of Genetic Syndromes. Copyright John Wiley & Sons Limited. Reproduced with permission.

Middle interhemispheric fusion (MIHF)
A. MRI in axial plane depicting middle interhemispheric variant of HPE in which the anterior portions of the frontal lobes and the occipital lobes are well separated. The sylvian fissures are oriented nearly vertically and are abnormally connected across the midline over the vertex of the brain (red/thin arrows). The genu and splenium of the corpus callosum appear normally formed, but the callosal body is typically absent. The hypothalamus and lentiform nuclei are normally separated; however, the caudate nuclei and the thalami remain incompletely separated.
B. The facial appearance is usually normal.
Gropman & Muenke [2005] Management of Genetic Syndromes. Wiley & Sons Limited. Reproduced with permission.

Semilobar HPE
A. MRI showing semilobar HPE. Note fusion of the frontal lobes, but presence of some septation posteriorly with presence of a falx and interhemispheric fissure (red/thin arrow). The splenium of the corpus callosum is present but more anterior portions are usually absent. A small, partially formed third ventricle is seen. More significant fusion of anterior brain structures (cortex, basal ganglia, thalamus) persists in this variant (blue/thick arrows). A dorsal cyst may be seen. In mild cases, lack of frontal horn development distinguishes this from the lobar type.
B. Note microcephaly, closely spaced eyes, depressed nasal ridge with cleft lip.
Gropman & Muenke [2005] Management of Genetic Syndromes. Copyright John Wiley & Sons Limited. Reproduced with permission.