What is Acrania?
Acrania:
"A fetal anomaly characterized by a partial or complete absence of the top portion of the skull, with complete but abnormal development of brain tissue. The condition is frequently associated with Anencephaly and is considered by the medical community as "not compatible with life". This anamaly appears during the beginning or end of the fourth week of fetal development, when the anterior neuropore closes. The desmocranium normally becomes the epidermis of the scalp, but in Acrania the desmocranium remains a membranous coverage. Therefore, the migration of mesenchmal tissue under the calvarium ectoderm does not happen; leading to an absence of the calvarial dermal bones of the skull, related musculature, and dura mater. The brain may still develop, but without the walls of the cranium shaping it, it will not differentiate between the two hemispheres and morph into a single mass that will not be able to sustain life. A developing baby is said to suffer from Acrania if it meets the following criteria: having a perfectly normal facial bone, a normal cervical column but without the fetal skull, and a volume of brain tissue equivalent to at least one third of the normal brain size. When only brain-stem was detected, the anomaly was referred to as Anencephaly."
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