What condition is characterized by the absence of a major portion of the brain, and is incompatible with life?

Anencephaly is a severe neural tube defect resulting in the absence of significant portions of the brain, including the cerebral hemispheres. This condition arises during early fetal development when the neural tube, which forms the brain and spinal cord, does not close completely. As a result, infants born with anencephaly typically have a rudimentary brain structure but lack the essential components necessary for higher brain functions and life-sustaining processes.

The prognosis for infants diagnosed with anencephaly is extremely poor, as they are often stillborn or live only a brief time after birth, primarily due to the vital functions that the absent brain structures would normally regulate. Therefore, anencephaly is understood to be incompatible with life as it encompasses a critical deficiency of essential neurological functions essential for survival.

In contrast, the other conditions listed, such as encephalitis, hydrocephalus, and microcephaly, do not represent the same level of absence or critical development failure seen in anencephaly and can present with varying degrees of life expectancy and potential for medical intervention.