Picture of the Month

Figure 1. A huge sacrococcygeal teratoma is attached to the infant's lower back. The cephalic portion of the tumor is necrotic.

Sacrococcygeal teratomas, although rare, are the most frequently recognized neoplasm in fetuses,¹ with an incidence of approximately 1 in 35,000 to 40,000 live births.¹ More common in female than male infants (4:1²), a familial predisposition is present in some cases.³ The incidence of twins in the immediate family varies from 14% to 50%.

Teratomas are congenital tumors composed of tissues derived from all 3 embryonic germinal layers. Postsacral tumors are thought to arise from multipotential embryonic cells that occur in greatest concentration in the area of the primitive knot (Hensen node) and presacral tumors from incomplete migration of germ cells from the yolk sac to the urogenital ridge.³ The female gonads of the fetus terminate their differentiation at 10 weeks' gestation in contrast to 7 weeks' for the male. The multipotential cells, therefore, remain longer in the female gonads and are more prone to disturbances, which may account for the higher incidence of sacrococcygeal teratomas in females.⁴ Sacrococcygeal teratomas may be the result of twinning or abortive attempts at twinning, which may account for the higher incidence in monozygotic twins.

Clinically, the tumor most commonly presents as a mass protruding between the coccyx and the anus, is usually covered with normal intact skin. Rarely, the skin may be necrotic owing to compromise in blood supply. Sacrococcygeal teratomas almost always arise from the tip of the coccyx and vary greatly in the amount of external vs internal tissue extensions. About 1% are intrapelvic with no external presentation and can only be diagnosed by rectal examination.⁵ They can be classified according to location into 4 types: type I, predominantly external with only a minimal presacral component; type II, external but with considerable intrapelvic extension; type III, apparent externally but the predominant mass is pelvic and extends into the abdomen; and type IV, presacral with no external presentation.

Approximately 2% to 10% of sacrococcygeal teratomas are malignant before the affected infant is age 2 months, 50% are malignant by age 1 year, and almost 100% are malignant by age 5 years.⁶ Malignant transformation is most likely to occur between age 4 months and 5 years.⁶ A tumor with a large presacral component may cause obstruction of the rectum, colon, or urinary tract.⁵ Occasionally, it may cause venous or lymphatic obstruction and paresis or paralysis of the lower limbs, especially if it is malignant.

Patients with large tumors early in gestation have a mortality rate higher than 50%.⁷ It has been suggested that arteriovenous shunting through a large tumor results in high-output cardiac failure, placentomegaly, fetal growth retardation, and hydrops fetalis.⁷ Severe dystocia with neonatal death may occur if the tumor is unsuspected prenatally and the infant is delivered vaginally. Approximately 15% of infants with these tumors have associated congenital anomalies such as anorectal malformations, sacral bone defects, and genitourinary abnormalities.⁸

A lateral radiograph of the abdomen may show anterior displacement of the rectum and possible calcification within the tumor. Abdominal and pelvic ultrasonography, computed tomography scanning, and magnetic resonance imaging help assess internal extension of the tumor, involvement of other organs, and existence of metastatic lesions. Serum α₁-fetoprotein levels are elevated in 70% of children with malignant tumors, with normal levels in children with benign tumors.⁹

The treatment of choice is complete resection of the tumor and coccyx. Failure to remove the coccyx will result in local recurrence in 30% of cases.¹⁰ Malignant recurrences have been reported in patients with previously benign tumors.¹¹ If the tumor is not resectable, chemotherapy may shrink it and render it resectable. The prognosis is excellent for children whose tumors are excised, along with the coccyx, soon after birth, with a cure rate of 90%.¹¹ Patients with malignant sacrococcygeal tumors have a poor prognosis (mortality rate >90%).

Accepted for publication September 10, 1999.

Reprints: Alexander K. C. Leung, MBBS, Alberta Children's Hospital, 1820 Richmond Rd SW, Calgary, Alberta, Canada T2T 5C7.