TABLE I.

Descriptions Of Typical Brain Findings In Each Of The Types Of Holoprosencephaly

	Alobar	Semilobar	Lobar	MIHV*	Microform
Interhemispheric separation	Complete or near-complete nonseparation, with absent falx cerebri	No anterior separation, some posterior separation	Nonseparation of only the most rostral/ventral frontal neocortex, with hypoplastic falx cerebri	Nonseparation of posterior frontal and parietal lobes	No interhemispheric fusion
Corpus callosal characteristics	Absent corpus callosum	Absent anterior corpus callosum	Absent corpus callosum in affected region	Absent body of the corpus callosum	May have subtle defects
Additional findings	Absent olfactory bulbs, fused deep gray nuclei, and single midline monoventricle	Absent or hypoplastic olfactory bulbs, fused deep gray nuclei, and absent anterior horns of lateral ventricles and septum pellucidum	Hypoplastic olfactory bulbs, hypoplastic falx cerebri, and azygous anterior cerebral artery	Frequent fusion of thalami and caudate nuclei, Gray matter heterotopias, cortical dysplasia, and Azygous anterior cerebral artery	May have subtle midline brain defects

^*MIHV: middle interhemispheric variant; Reproduced with permission from reference 10.