I can understand your concern after the scan report however i believe according to your scan you are around 31 weeks pregnant and in your case there is only isolated dilatation of left ventricle. However in your case there is no corpus callosum agenesis.First and foremost we need to see the dimensions of the ventricle to guage how much is the dilatation. Secondly we need to go back to your previous reports of your nuchal scan done at 10-12 weeks , tripple or quadruple marker and anomaly scan done around 18-20 weeks. If the above are normal , it is not of much of a concern also the biophysical profile and dopplers are normal suggesting that the baby is fine.