Definition: This tumor, derived from the three germinal layers is found frequently in the sacrococcygeal region. In fact, this is the most frequent site of teratomas of the fetus.
Prevalence: The incidence is 1 in 35,000 to 1 in 40,000 live births. Females are four times more likely to be affected than males, but malignant change is seen more frequently in males.
Etiology: The etiology is unknown, but has been suggested that it is derived from totipotential cells in Hensen's node. A theory of "twinning accidentâ€ with incomplete separation during embryogenesis has also been proposed. Some cases of sacrococcygeal teratoma are familial, with autosomal dominant inheritance.
Ultrasound features: Most sacrococcygeal teratomas appear solid or mixed solid and cystic, containing randomly arranged, irregularly shaped cysts. Occasionally the tumor displays a solid, or more often a completely cystic variant. Most teratomas are extremely vascular, which is easily shown using color Doppler technique. Polyhydramnios is frequent, and its mechanism is unclear. Secondary to high output cardiac failure, hepatomegaly, placentomegaly and hydrops fetalis can occur. High output failure is the result of tumor hemorrhage and/or arteriovenous shunting.