October 2015

A 6-day-old baby girl with a sacral mass

Maggie Yell, MD and Kymberly A. Gyure, MD


A 6-day-old baby girl was found to have a sacral mass which was diagnosed in utero via ultrasound. She was born at 30 2/7 weeks gestation via cesarean section due to worsening maternal pre-eclampsia. The mass was external to the sacral spine and did not involve the genitalia. The patient was non-hydropic. Surgical excision of the sacral mass was performed.

Gross Description

The specimen consisted of a 600-gram, 15.0 x 8.5 x 7.6 cm mass with erosion of the overlying skin. Its cut surfaces were variegated and lobulated with cystic areas, hemorrhage, and cartilage formation (Figure 1).

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Figure 1: Cut surfaces of the specimen.

Representative microscopic sections of the mass are shown below (Figures 2-5):

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Figure 2 (20x magnification): The mass is composed of a mixture of cystic and solid components. Cartilage formation is present.
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Figure 3 (20x magnification): The mass also contains mature fat and cystic areas containing papillary structures.
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Figure 4 (200x magnification): The cystic spaces are lined by respiratory epithelium.
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Figure 5 (200x magnification). Foci of primitive neuroectodermal tissue with rosette-like structures resembling the developing neural tube are found within the mass.


What is the diagnosis?


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Sacrococcygeal teratomas are one of the most common congenital and neonatal neoplasms. In general, teratomas are the most common type of germ cell tumor and frequently occur in gonadal, sacrococcygeal, mediastinal, and retroperitoneal locations (1). Sacrococcygeal teratomas occur in approximately 1 in 27,000 live births (2).

Sacrococcygeal teratomas occur mostly in infants and children with a female predominance (2). The sacrococcygeal site is the most common location for teratomas during infancy and the neonatal period but is a rare location for teratomas found during adolescence. The majority are mature, but some (as in this case) have immature components.

Neonatal sacrococcygeal teratomas are usually diagnosed in utero via ultrasound (US) or magnetic resonance imaging (MRI). Ultrasound findings consist of a large, solid coccygeal mass or multicystic sacral mass that communicates with a pelvic mass. Alpha fetoprotein (AFP) levels may be elevated in infants with sacrococcygeal teratomas (2). An in utero diagnosis warrants close surveillance with ultrasounds and echocardiography in order to determine whether early fetal intervention is necessary (3).

Macroscopically, sacrococcygeal teratomas are cystic, solid, or a mixture of both with varying amounts of necrosis. In contrast to gonadal teratomas, sacrococcygeal teratomas frequently do not have a capsule, rendering complete resection of the tumor challenging. The tumor may have a solid, brain-like cut surface in instances with prominent neural or glial differentiation (4).

Microscopically, sacrococcygeal teratomas are histologically classified as mature, immature, or malignant. They contain components of all three germ cell layers (ectoderm, mesoderm, and endoderm) (1,4). Mature teratomas are composed of completely differentiated somatic tissues arranged in a disorganized pattern, sometimes referred to as a “histologic potpourri” (4). These somatic tissues can include cysts that are lined by epithelium, mature smooth/striated muscle, or cartilage (5). Complex organ structures such as pancreatic tissue or intestinal segments may also be seen in mature teratomas (4).

Immature teratomas have all the components seen in mature teratomas; however, they must also include immature elements or incompletely differentiated tissue. These immature elements are usually primitive neuroectodermal tissue arranged in rosette-like structure of primitive neurotubules or neuroblastomatous foci. Ki-67 immunostaining may be used to assess the proliferation rate, which correlates with the extent of immaturity. In rare instances, there can be nephroblastomatous foci characteristic of Wilms tumor (1,4).

Histologic malignant components can be of non-germ cell origin or be of germ cell origin, usually a yolk sac tumor. Yolk sac tumor foci can be detected by alpha fetoprotein (AFP) immunostaining (4,6).

The prognosis for pure sacrococcygeal teratomas (no malignant component) in neonates is favorable (3). The majority of live born infants with sacrococcygeal teratomas survive surgical resection and have a good prognosis (2). Age at the time of diagnosis has a significant impact on prognosis. There is a worse prognosis when the tumor is detected at an earlier gestational age, which is probably due to the fact that larger tumors are visible earlier than smaller tumors (3). Most children who present after the neonatal period have histologic features of malignancy (2). Sacrococcygeal masses that present during late infancy and early childhood tend to be yolk sac tumors with or without a teratoma component. Half of relapses following incomplete resection of teratomas have a component of malignant yolk sac tumor (4).

Large, solid, and highly vascular sacrococcygeal teratomas have increased mortality and morbidity. TFR (tumor volume to fetal weight ratio), as measured via ultrasound, can be used as an objective predictor of outcome in fetuses with a sacrococcygeal tumor prior to 24 weeks gestation. A TFR of less than or equal to 0.12 prior to 24 weeks gestational age has a more favorable prognosis. Tumors with greater than 50% solid components measured on ultrasound have a worse prognosis since solid tumors tend to be more vascular than cystic tumors. Vascularity of the tumor is significant as blood is shunted away from the placenta and to the tumor, resulting in fetal anemia and development of high-output cardiac failure. This leads to polyhydramnios, which can lead to premature labor. High-output cardiac failure can also cause placentomegaly and fetal hydrops (3).

Some sacrococcygeal tumors may be associated with other cardiac, nervous, urogenital, or musculoskeletal abnormalities. A population based cohort study done by Swamy et al. found associated congenital anomalies which included exomphalos, scoliosis, bilateral hydroceles, truncus arteriosus, cerebral ventriculomegaly, and cleft palate (2).