Holoprosencephalies are disorders characterized by failure of differentiation and midline cleavage of the prosencephalon. As a result, parts of the brain that are normally located more laterally lie close to or within the midline and may be fused across the rostral midline. Sagittal T1-weighted (A) MRI shows truncation of anterior corpus callosum (arrow), with absence of the inferior genu and rostrum. Gyration of frontal lobes is primitive. Coronal T1-weighted (B) image shows continuity of basal ganglia (arrowheads) across midline and absence of frontal horns of the lateral ventricles. Transverse axial T2-weighted (C) image shows continuity of white matter across ventral midline and neither discrete basal ganglia nor third ventricle is seen.
