Anencephaly: Short Notes

Definition:
Absence of the calvaria above the bony orbits. May be associated with absence of cerebral hemisphere.

Incidence:
1/1000 live births.

Pathogenesis:
Failure of closure of cephalad neural tube at 25 - 27 days post conception.

Risk of Recurrence:
2 - 4 % with 1 affected siblings. 10% with 2 affected siblings.

Diagnosis (Antenatal):

• Absent bony calvaria
• Orbits well visualized
• Absence of supratentorial brain
• Residual brain
• Associated polyhydromnios, due to decreased fetal swallowing
• Associated spina bifida

Associated Anomalies:

• Spina bifida
• Urinary tract anomalies
• Cleft lip / palate
• GIT anomalies (ie. omphalocoele, intestinal aganglionosis)
• Cardiac anomalies

Prognosis:
Incompatible with life. Some may live up to a week postnatally.

Prevention:
Folic acid supplements, recommended 4 mg per day a month preconception and 3 months after.
With-holding anticonvulsants (folic acid antagonist, ie. valproate, carbamezapine, phenytoin, trimetoprim)


References
1. Nyberg, David A., et al., Diagnostic Imaging of Fetal Anomalies, Lippincott Williams & Wilkins, 2003.

2. Tomita T., et al., Anencephaly, UpToDate Article, 2012.

Future Topics:
- Folic acid in prevention of neural tube defects.
- Feasibility of organ donation of anencephalic babies
- Spina bifida and other neural tube defects.