This site is targeted at medical and radiology professionals, contains user contributed content, and material that may be confusing to a lay audience. Use of this site implies acceptance of our Terms of Use.

Anencephaly

Anencephaly is the most severe form of cranial neural tube defect (NTD) and is characterised by absence of cortical tissue (although brainstem and cerebellum may be variably present) as well as absence of the cranial vault. Morphologcial spectrum within anencephaly ranges from holocrania (severest form) to merocrania (mildest form) 2

Epidemiology

Incidence is around 1 : 1000. There is a recognised female predilection with a F : M of ~ 4 : 1.

As with many other malformations, a number of associated abnormalities are recognised:

Clinical presentation

In affluent nations the diagnosis is usually made antenatally. At birth the diagnosis is made due to obvious malformation of the cranial vault. 

Pathology

It results from a failure of closure of antral end of neural tube which is expected to occur at approximately 24 days of fetal life. 

Markers

Radiographic features

Antenatal ultrasound

Anencephaly may be sonographically detectable as early as 11 weeks. Ultrasound can be a non invasive, cost effective and fast method to detect anencephaly and has an accuracy of approximating 100 % at 14 weeks

  • no tissue above the orbits and absent calvarium : parts of the occipital bone and mid brain may be present 
  • if a small amount of neural tissue is present it is then termed exencephaly
    • this may be seen at an earlier stage
  • less than expected value for crown rump length (CRL)
  • a "frog eye" or "mickey mouse" appearance may be seen when seen in the coronal plane due to absent cranial bone / brain and bulging orbits.
  • may show evidence of polyhydramnios : from impaired swallowing

Treatment and prognosis

Not surprisingly anencephaly is incompatible with life. Folic acid therapy may reduce risk of recurrence. There is a slight risk (~ 2.5 %) in recurrence of a neural tube defect in future pregnancies.

Differential diagnosis

Anencephaly should not be confused with hydranencephaly in which the cranial vault is present and absence of cerebral tissue is due to antenatal vascular insult.

See also

Updating… Please wait.
Loadinganimation

Alert_accept

Error Unable to process the form. Check for errors and try again.

Alert_accept Thank you for updating your details.