Acrania

Acrania is a cephalic disorder of a human fetus characterised by a partial or complete absence of the cranium. The condition is frequently, though not always, associated with anencephaly. The anomaly Acrania is a partial or complete absence of the calvarium with abnormal brain tissue development. This anomaly is lethal in all cases and has important implications for obstetrical management and counseling. Acrania can be diagnosed early in pregnancy through an ultrasound. The fetus is said to suffer from acrania if it meets the following criteria: the fetus should have 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 no brain or little traces of it are detected, the anomaly is referred to as Anencephaly.^[1]

Diagnosis

Ultrasound can be involved in diagnosis.This anomaly appears during the beginning or end of the fourth week of the fetus' 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 ^[1]. The brain may still develop normally, but without the walls of the cranium shaping it, it will not differentiate between the two hemispheres and will morph into a single mass that will not be able to sustain life. Acrania is in all cases lethal; no human being can live without the skull and there is no technology that is able to keep victims of this anomaly alive for a longer time. The difference between acrania and anencephaly is that acrania is the absence of the cranium but anencephaly is the absence of the brain. The brain can still be formed in acrania.^[2]

Prognosis

Whether diagnosed during pregnancy or at birth, the condition is invariably fatal.^[1]

See also

• Acalvaria

References

1. ^ ^{a b c} Acrania: review of 13 cases - Tae-Hee Kwon, MD*, Jim King, MD, Philippe Jeanty, MD, PhD
2. ^ Liu IF, Chang CH, Yu CH, Cheng YC, Chang FM (2005). "Prenatal diagnosis of fetal acrania using three-dimensional ultrasound". Ultrasound in medicine & biology 31 (2): 175–178. doi:10.1016/j.ultrasmedbio.2004.10.005. PMID 15708455. 

• Acalvaria (Acrania) at NIH's Office of Rare Diseases