Welcome to the Rare Classroom, a new series from Patient Worthy. Rare Classroom is designed for the curious reader who wants to get informed on some of the rarest, most mysterious diseases and conditions. There are thousands of rare diseases out there, but only a very small number of them have viable treatments and regularly make the news. This series is an opportunity to learn the basics about some of the diseases that almost no one hears much about or that we otherwise haven’t been able to report on very often.

Eyes front and ears open. Class is now in session.

The disease that we will be learning about today is:

Acalvaria

What is Acalvaria?

• Acalvaria is a very rare malformation that appears during birth in which the calvarial bones, dura mater, and accompanying muscles and facial bones are absent
• In effect, there is only a layer of skin covering the top of the brain instead of the skull cap
• This layer of skin varies in size depending on the case
• Often the rest of the central nervous system remains unaffected
• People born with the malformation rarely survive birth

How Do You Get it?

• The cause of acalvaria is unknown
• Scientists theorize that the membranous neurocranium migrates abnormally in respect to the typical positioning of the ectoderm.
  • During normal development, the anterior neural pore closes after about a month. The mesenchymal tissue then migrates beneath the ectoderm.
  • In acalvaria, the migration of this tissue doesn’t occur correctly.
• Acalvaria is classified as a postneurulation defect, meaning that it takes place between day 24 to day 26 of development.
• Female fetuses are at a higher risk of the defect.

What Are The Symptoms?

• This malformation is usually diagnosed using ultrasonography before birth.
• There are four main signs of acalvaria which include:
  • Absent skull cap
  • Absence of the flat cranial vault bones
  • Skull abnormalities
  • Absent dura mater and accompanying muscles
• Significant cognitive and physical impairment is possible in patients that survive birth.

How Is It Treated?

• Treatment is very limited as there are very few people that survive birth with the condition.
• Acalvaria must be monitored very closely, and often a bone graft is necessary as the child gets older.

Where Can I Learn More???

• Check out our cornerstone on this disease here.
• Learn more about this condition from the National Organization for Rare Disorders.