Acalvaria
Acalvaria is a rare malformation consisting of absence of the calvarial bones, dura mater and associated muscles in the presence of a normal skull base and normal facial bones. The central nervous system is usually unaffected. The presumed pathogenesis of acalvaria is faulty migration of the membranous neurocranium with normal placement of the embryonic ectoderm, resulting in absence of the calvaria but an intact layer of skin over the brain parenchyma. In other words, instead of having a skull cap protecting the brain, there is only skin covering it [1]. The size of the area that is missing the skull cap can vary from case to case. In extreme cases, the entire top part of the cranium that is dome-shaped may be absent[2].
Pathogenesis
Currently there is no identified cause of acalvaria[1]. The primary presumed pathogenesis is problematic migration of the membranous neurocranium with respect to the normal positioning of the immature ectoderm[2]. When an embryo develops normally, the anterior neural pore closes about the fourth week. After this occurs, mesenchymal tissue migrates under the ectoderm. This ectoderm underlies where the cerebral hemisphere will eventually be. When a fetus has acalvaria, the embryonic ectoderm is in its correct place, but the mesenchymal migration does not occur correctly. Therefore, acalvaria is considered to be a postneurulation defect[3]. Because it is a postneurulation defect, it must develop after embryonic stage 11, between 24 and 26 days after conception[4].
Signs, Symptoms, and Diagnosis
There are four main symptoms of acalvaria: absence of the flat bones of the cranial vault, absence of the dura mater and muscles associated with it, skull abnormalities, and the absence of a skull cap[1]. This condition can be diagnosed prior to birth using ultrasonography. Physicians often use magnetic resonance imaging to confirm the diagnosis because in utero, acalvaria sometimes confused with anencephaly or encephalocele[2].
References
- ^ a b c "Acalvaria." Right Diagnosis. Health Grades Inc., n.d. Web. 27 Nov. 2012. <http://www.rightdiagnosis.com/a/acalvaria/intro.htm
- ^ a b c "Acalvaria." Orphanet. N.p., n.d. Web. 18 Nov. 2012. <http://www.orpha.net/consor/cgi-bin/OC_Exp.php?lng=EN
- ^ Khadilkar, V. V., A. V. Khadilkar, A. A. Nimbalkar, and A. S. Kinnare. "Acalvaria." Acalvaria. N.p., 17 June 2004. Web. 20 Nov. 2012. <http://medind.nic.in/ibv/t04/i6/ibvt04i6p618.pdf
- ^ Moore, Kathleen, Raj P. Kapur, Joseph R. Siebert, Wendy Atkinson, and Thomas Winter. "Acalvaria and Hydrocephalus: A Case Report and Discussion of the Literature." Journal of Ultrasound Medicine 18 (1999): 783-87. American Institute of Ultrasound in Medicine. Web. 18 Nov. 2012. <http://www.jultrasoundmed.org/content/18/11/783.full.pdf
External links
- Harris CP, Townsend JJ, Carey JC (1993). "Acalvaria: a unique congenital anomaly". Am J Med Genet. 46 (6): 694–699. doi:10.1002/ajmg.1320460620. PMID 8362912.
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