anencephaly

n. congenital absence of the brain

Anencephaly is a cephalic disorder that results from a neural tube defect that occurs when the cephalic (head) end of the neural tube fails to close, usually between the 23rd and 26th day of pregnancy, resulting in the absence of a major portion of the brain, skull, and scalp. Infants with this disorder are born without a forebrain, the largest part of the brain consisting mainly of the cerebral hemispheres (which include the isocortex, which is responsible for higher level cognition, i.e., thinking). The remaining brain tissue is often exposed - not covered by bone or skin.
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Anencephaly /an·en·ceph·a·ly/ congenital absence of the cranial vault, with the cerebral hemispheres completely missing or reduced to small masses. [more]Anencephaly - Community and Resources

Noun
1. a defect in brain development resulting in small or missing brain hemispheres
(synonym) anencephalia
(hypernym) birth defect, congenital anomaly, congenital defect, congenital disorder, congenital abnormality

noun
absence of a brain, which causes a fetus to die a few hours after birth