Prevalence:

• 1 in 20,000 births.
• It is the most frequent fetal teratoma.

Ultrasound diagnosis:

• Usually mixed solid and cystic (multiple cysts irregular in shape and size).
• The tumors may be entirely external, partially internal and partly external, or mainly internal.
• Most teratomas are extremely vascular, which is easily shown using color Doppler ultrasound.

Associated abnormalities:

• The incidence of chromosomal defects or genetic syndromes is not increased.
• Hydronephrosis due to ureteric compression in the case of internal tumors.

• Large tumours may result in fetal anemia and thrombocytopenia (due to sequestration of red blood cells and platelets by the tumor), fetal heart failure, hydrops and placentomegaly (due to a hyperdynamic circulation as a result of arteriovenous shunting), polyhydramnios (due to direct transudation into the amniotic fluid and due to fetal polyuria, secondary to the hyperdynamic circulation) and maternal mirror syndrome (generalized fluid overload and preeclampsia).

Investigations:

• Detailed ultrasound examination, including echocardiography for assessment of cardiac function and measurement of fetal middle cerebral artery peak systolic velocity (MCA PSV) for diagnosis of fetal anemia.

Follow-up:

• Follow-up scans every 2 to 3 weeks to monitor growth of the tumor, heart function, MCA PSV and amniotic fluid volume.

• Ultrasound guided laser coagulation of vessels within the tumor, fetal blood transfusions and amniodrainage may become necessary.

Delivery:

• Place: hospital with neonatal intensive care and pediatric surgery.
• Time: 38 weeks. Earlier if there is evidence of poor growth, fetal hypoxia or hydrops.
• Method: cesarean section if the tumor is very large and there is evidence of heart failure.

Prognosis:

• Perinatal mortality: about 50%, mainly due to the preterm birth (the consequence of polyhydramnios) of a hydropic infant requiring major neonatal surgery.
• Difficult surgery, especially with tumors that extend into the pelvis and abdomen, can result in nerve injury and incontinence.
• The tumor is invariably benign in the neonatal period but delayed surgery or incomplete excision can result in malignant transformation (about 10% before 2 months of age to about 80% by 4 months).

Recurrence:

• No increased risk of recurrence.