It is a rare congenital disorder that occurs in the human fetus, in which the flat bones of the cranial vault are totally or partially absent.
The cerebral hemispheres develop ultimately but abnormally.
It is said that the fetus suffers from Acrania if it meets the following criteria:
It must have a perfectly normal facial bone, a normal cervical spine but without the fetal skull, and brain tissue volume equivalent to at least one-third of the normal brain.
It is hypothesized that there are multiple origins for Acrania, like other malformations of development. Recent work has identified mutations in the HHAT gene that have caused Acrania, holoprosencephaly, and Egnatia.
The sequence of acrania anencephaly begins with Acrania, the most common anomaly affecting the central nervous system, with an incidence of 1 in 1000 pregnancies.
It occurs when the anterior neuropore is closed at the beginning of the fourth week of gestation. The regular migration of mesenchymal tissue to form the skull does not happen.
The overlying ectoderm remains the only coating like a thin membrane similar to an amnion. The calotte, the muscles of the scalp, and the dura mater are not formed.
In the absence of neurocranium induction, brain tissue does not differentiate into two hemispheres. In this way, the brain is exposed to amniotic fluid with a risk of friction with the uterine wall, the placenta, and the fetal parts.
In this circumstance, the unprotected brain tissue suffers destruction and progressive degeneration due to mechanical and chemical trauma, leading to the complete disappearance of the brain after 14 weeks of gestation.
There is a 100% mortality rate for those with Acrania. This disease is rare and occurs in 1 in 20,000 live births.
Early detection is of extreme importance to better manage a diagnosis of this anomaly so that measures can be taken to help the mother and the child.
Families can choose to terminate the pregnancy or carry it to term. It is important to note that Acrania can cause a fetus to abort spontaneously before reaching the end.
Many fetuses with this condition also have anencephaly, where part of the brain is missing, and the skull and scalp are. Heart defects, cleft lip, and gastrointestinal abnormalities may also occur.
These defects may not be diagnosed unless the parents specifically request an autopsy.
It can be diagnosed early in pregnancy through an ultrasound. This anomaly appears during the beginning of the end of the fourth week of the development of the fetus. An absence of the skull is needed to make a diagnosis.
The presence of brain tissue will confirm the diagnosis of Acrania and differentiate it from other developmental problems such as anencephaly. In ultrasound, damaged brain tissue can be seen as echogenic particles in the amniotic fluid.
In the first trimester examinations, there is an average amount of brain tissue present that, when seen in the coronal plane of the fetus, results in the “Mickey Mouse” sign due to two semicircular structures that float on the fetal face as well as the rounded ears.
In the second trimester, a significant amount of brain tissue is lost, which results in the sign of the frog’s face due to the absence of recognizable tissue superior to the level of the fetal orbits.
Acrania has no known family links, and the recurrence rates are meager. We still do not know much about the exact mechanism in this rare condition.
Unfortunately, there is no medical treatment for Acrania. Due to the lack of brain development in babies, approximately 75% of babies are stillborn, and the other 25% die within a few hours, days, or weeks after delivery.
The focus is on providing emotional support to your family. Many families find comfort in knowing that their child has not been forgotten by those who cared for him and others who share their pain.
In addition, genetic counseling is recommended for parents to discuss the risk of recurrence in a future pregnancy and vitamin therapy.