Acrania vs. Anencephaly — What's the Difference?

Acrania is an early developmental anomaly in which the flat bones of the cranial vault are missing, but the cranial base and facial bones are usually normal. This condition allows for the brain tissue to develop, although it is often abnormal and exposed. On the other hand, anencephaly involves the absence of a major portion of the brain, skull, and scalp. Occurring during embryonic development, it is considered one of the most severe neural tube defects. While both conditions result from abnormal neural tube closure, anencephaly is more severe, typically leading to stillbirth or death shortly after birth.

In acrania, the absence of cranial bones leads to the exposure of the cerebral hemispheres, which are not covered by bone or skin, making survival outside the womb virtually impossible. Whereas in anencephaly, the brain's development is so compromised that most of the brain tissue is missing, and what remains is often not covered by bone or skin. This distinction underscores the severity and outcomes of these conditions, with anencephaly being more uniformly fatal.

Diagnosis of acrania and anencephaly usually occurs via prenatal ultrasound, with both conditions detectable in the first trimester. However, the prognosis for each is grim, with no viable treatments to correct the defects. The emphasis is often on supportive care and counseling for the affected families. Despite the similarities in early detection and lack of treatment, the specific nature and prognosis of these conditions differ markedly.

Research into the causes of acrania and anencephaly focuses on genetic, environmental, and nutritional factors, with particular attention to folic acid deficiency during pregnancy. While the exact mechanisms leading to these conditions are not fully understood, the importance of prenatal care and nutritional supplementation is emphasized in preventing neural tube defects.

While acrania and anencephaly are related developmental conditions resulting from neural tube defects, they are distinct in their presentation, severity, and outcome. Acrania involves primarily the absence of the skull with some brain development, whereas anencephaly is characterized by the absence of significant portions of the brain and skull.