What sonographic findings are associated with holoprosencephaly?

1. Fusion of the thalami (seen in lobar and semilobar holoprosencephaly)
2. Presence of a dorsal sac (i.e., a fluid-filled intracranial space with monoventricle)
3. Absence of the falx and septum pellucidum
4. Midline facial abnormalities
5. Abnormalities of the cardiovascular and gastrointestinal systems, abnormal hands, and spina bifida