ANENCEPHALY
 
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ANENCEPHALY

 

DEFINITION:

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

EPIDEMIOLOGY:

  • incidence: 1/1000 live births
  • age of onset:
    • newborn
  • risk factors:
    • geographic
      • variable with incidence increased in Ireland and Wales and decreased in Asia, Africa, and South America
    • genetic
      • recurrence rate is 4% and increases to 10% if a couple has had 2 previous anencephalic infants
      • whites > blacks (6:1)
      • F > M
    • environmental/nutritional
      • low SEC, environmental and toxic factors
      • nutritional and vitamin deficiences
      • folic acid antagonists
      • drinking water minerals
    • perinatal
      • maternal infections and/or hyperthermia
  • associated anomalies:
    • 50% polyhydramnios (unable to swallow amniotic fluid)
    • 10-20% folded ears, cleft palate, congenital heart disease

 

PATHOGENESIS:

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

CLINICAL FEATURES:

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

INVESTIGATIONS:

1. Prenatal Diagnosis

  • elevated maternal serum alpha-feto-protein (AFP)
  • level II ultrasound
  • amniocentesis - elevated AFP and acetylcholinesterase

MANAGEMENT:

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

 

 

 

 

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