Prevalence:

• 1 in 25,000 births.

Ultrasound diagnosis:

• Supratentorial mid-line translucent elongated cyst with active arteriovenous flow within the cyst demonstrated by color Doppler.
• The defect develops in the early first trimester, but the aneurysm becomes sonographically apparent just in the third trimester.
• In 90% of cases there is high-output heart failure with secondary hydrops.

Associated abnormalities:

• The incidence of chromosomal abnormalities or genetic syndromes is not increased.

Investigations:

• Neurosonography to exclude secondary brain lesions (ischemia and leukomalacia).
• Echocardiography for detection of early signs of heart failure.

Follow up:

• Follow-up scans should be arranged every 1 week, mainly to determine the time of delivery depending on the risk of developing heart failure.

Delivery:

• Place: hospital with neonatal intensive care and pediatric surgery.
• Time: 38 weeks.
• Method: cesarean section.

Prognosis:

• One third have a good outcome after postnatal intervention by embolization. One third die during the procedure and one third survive but with neurodevelopmenal delay.
• If there is hydrops fetalis at the time of diagnosis then the prognosis is poor.

Recurrence risk:

• No increased risk of recurrence.