Site hosted by Build your free website today!



A neural tube defect affecting the skull resulting in a large defect of the calvarium, meninges, and scalp which is incompatible with life.


*incidence: 1/1000 live births

*age of onset:

*risk factors:


--variable with incidence increased in Ireland and Wales and decreased in Asia, Africa, and South America


--recurrence rate is 4% and increases to 10% if a couple has had 2 previous anencephalic infants
--whites > blacks (6:1)
--F > M


--low SEC, environmental and toxic factors
--nutritional and vitamin deficiences
--folic acid antagonists
--drinking water minerals


--maternal infections and/or hyperthermia

*associated anomalies:

--50% polyhydramnios (unable to swallow amniotic fluid)
--10-20% folded ears, cleft palate, congenital heart disease


1. Background

*anencephaly arises from an embryonic defect occurring prior to day 26 which prevents the closure of the anterior neuropore - the frequency of anencephaly has decreased during past 2 decades - CNS findings:

--both cerebral hemispheres and thus the spinal cord pyramidal tracts are absent
--absence of the cerebellum
--residue of the brainstem usually present
--hypoplastic pituitary gland
--the rudimentary brain remaining consists of portions of con-nective tissue, vessels, and neuroglia


1. Anencephaly

*distinctive appearance: a large defect in the vault of the skull (calvarium), meninges, and scalp exposes a soft angiomatous mass of neural tissue covered with a thin membrane continuous with the skin

*the cranial defect may extend inferiorly to the cervical region exposing a thin and flattened spinal cord (craniorachischisis)

*the optic globes may protrude due to inadequately-formed bony orbits

2. Neuroendocrine Defects

*hypoplastic pituitary

--adrenal insufficiency
--diabetes insipidus


1. Prenatal Diagnosis

*elevated maternal serum alpha-feto-protein (AFP)

*level II ultrasound

*amniocentesis - elevated AFP and acetylcholinesterase


1. No Treatment

*most infants are stillborn or die within several days of birth

*organ donation is controversial

2. Genetic Counselling

*amniocentesis, AFP, and/or an ultrasound between 14-16 weeks in couples with a history of an anencephalic infant