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[1].

Etiology:  The etiology is unknown, but has been suggested that it is derived from totipotential cells in Hensen's node. A theory of "twinning accident†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.

Ultrasound picture of a sacrococcygeal teratoma diagnosed at 17 weeks of pregnancy. Note the huge cystic mass originating from the fetal sacrum (arrow).

Post abortion picture of the fetus.

Prognosis: The mortality rate of fetal sacrococcygeal teratoma approaches 50%, while the mortality in newborns is 5%. Most tumors are benign, but malignant change is a definite risk. The risk rises from 10% before 2 months of age to 65 to 90 percent if the diagnosis and surgical excision are delayed beyond 4 months of age. Other factors that may influence prognosis include tumor size, and presence of tumor hemorrhage. It should be remembered that this tumor tends to become large, and thus may cause obstetric complication such as dystocia and malpresentation.

References:

[1] Altman, R.P., Randolph, J.G., Lilley, J.R. Sacroccocygeal teratoma: American Academy of Pediatrics Surgical Section Survey. J Pediatr Surg 1974;9:389-398.