Holoprosencephaly can be divided into three categories, alobar, semilobar, and lobar depending on the degree of cleavage. Alobar holoprosencephaly is the most severe form. Findings of this type include absence of the interhemispheric fissure, a single primitive ventricle, fused thalami, and absent third ventricle, olfactory bulbs, and optic tracts. Semilobar holoprosencephaly is characterized by partially separated cerebral hemispheres and a single ventricular cavity. Facial anomalies, consisting of aplasia or hypoplasia of midline structures are characteristic of holoprosencephaly.
Prognosis depends on the type of holoprosencephaly and the presence of associated anomalies.
Chromosome abnormalities, especially trisomy 13 and 18, may be associated with holoprosencephaly. For this reason, if holoprosencephaly is identified, amniocentesis is recommended. Choroid plexus cysts are believed to result from the accumulation of CSF and cellular debris within the neuroepithelial folds. These cysts are found in approximately 50 percent of individuals of all ages in serial autopsy. These cysts can generally be visualized in the second trimester and usually resolve by 24 weeks gestation.