Measurements of routine head sonographic scans of 57 term infants with trisomy 21 born between 2000 and 2005 were performed within 7 days after birth and were compared with scans of 21 randomly selected, healthy, term infants without trisomy 21 at Shaare Zedek Medical Center, Jerusalem; Ben Gurion University of the Negev, Beer Sheva; and Hadassah University Hospital, Jerusalem, Israel. The test and control neonates were the same gestational ages (39+/-1 weeks), but trisomy 21 infants were smaller and had smaller head circumferences than controls (32.9 cm vs 34.9 cm; P=0.001). The width and length of the third ventricle were increased in infants with trisomy 21. Vertical measurements of the lateral ventricle were similar for the 2 groups. 
COMMENT. The authors speculate that the enlargement of the third ventricle demonstrated in neonates with trisomy 21 may reflect hypoplasia of the thalamus, hypothalamus, and deep white matter, which are involved in cognitive processes of attention, verbal and visuospatial memory. Prefrontal, cerebellar, and hippocampal functions are also affected in trisomy 21.