Holoprocencephaly

Holoprocencephaly with an associated fused metopic suture /single frontal "plate" of bone. 

Formerly called arrhinencephaly. 

Best diagnostic clue is Monoventricle + fused (uncleaved) frontal lobes ~ absent anterior midline falx/fissures and Anteriorly displaced Sylvian fissures. 

Associated with Hypotelorism, fused metopic suture /single frontal "plate" of bone, Azygous / absent anterior cerebral artery (ACA) on MR Angio.