The Case of antenatally diagnosed sacral mass

The Case:
A female neonate who had an antenatally diagnosed sacral mass is admitted to the neonatal intensive care unit immediately after birth.

Figure 1

Prenatal History:
The 26-year-old mother had two previous normal pregnancies. In the current pregnancy, a mass was discovered at 20 weeks’ gestation. The woman underwent serial ultrasonographic imaging to monitor the mass. Fetal magnetic resonance imaging obtained at 24 weeks’ gestation revealed a mixed solid-cystic mass in the sacrococcygeal region, extending inferiorly (Figure 2). Elective cesarean section is performed at 37 weeks’ gestation
Birth History and Presentation:

• Apgar scores of 8 at 1 minute and 9 at 5 minutes
• Term female infant has a 14×15–cm mass attached caudally to the sacrum (Figure 1)
• Mass does not transilluminate, has vessels coursing over the surface, and is palpably solid in some places and cystic in others

Figure 2

 Case Progression:
Abdominal radiographs reveal a 13×15-cm broad-based pedunculated soft-tissue mass projecting from the lower sacrococcygeal area (Figure 3).

Figure 3

Postnatal ultrasonography demonstrates a large mass posterior to the coccyx. The mass has a heterogeneous echotexture with solid, cystic, and vascular components. The lower spinal canal appears normal. Serum α-fetoprotein (AFP) concentration is 335,700 ng/mL (35,700 µg/L). The infant undergoes surgery on the third day after birth. Histopathologic examination of the surgical specimen reveals the presence of mature neuroglial tissue, choroid plexus, adipose tissue, smooth muscle cells, squamous epithelium, cartilage, and bone (Figures 4 and 5).

Figure 4 and 5

Differential Diagnosis:
Newborn who has a sacral mass

• Lipoma
• Lymphangioma
• Meningocele
• Rhabdomyosarcoma
• Sacrococcygeal teratoma
• Other malignant pediatric neoplasms

Actual Diagnosis: 
Sacrococcygeal teratoma (SCT)

The Experts:
SCTs are the most common tumors in newborns, occurring in 1 per 20,000 to 40,000 births. Females are four times more likely to be affected than males, but malignant change is seen more frequently in males. Sizes range from 1 to 30 cm, and a large teratoma may account for half of a newborn’s weight. SCTs are believed to arise from embryologically multipotent cells of Hensen’s node, which lies within the coccyx.
The outcome for SCTs diagnosed in utero is much worse than those diagnosed in the neonatal period; the survival rate was 53% in fetuses compared with 85% in neonates in one large series. Potential complications in utero include polyhydramnios, tumor hemorrhage, anemia, congestive heart failure, and nonimmune hydrops fetalis. Development of hydrops is an ominous sign. The presence of hydrops before 30 weeks’ gestation has an abysmal prognosis, with a 93% mortality rate. Because of the poor prognosis associated with development of hydrops prior to 28 to 30 weeks’ gestation, affected fetuses may benefit from in utero resection of the tumor that resolves the hydrops. Development of hydrops after 30 weeks’ gestation is associated with a mortality rate of 25%. If recognized, delivery is recommended as soon as lung maturity is documented. For fetuses that have tumors larger than 5 cm, cesarean delivery should be considered to prevent dystocia or tumor rupture.
SCTs can be diagnosed prenatally as early as 13 weeks of gestation. Ultrasonography reveals a nonhomogenous sacral mass, with calcification in one third of cases. It also defines the extension of the tumor into the pelvis or abdomen as well as mass displacement of the bladder and rectum, with compression of the ureters resulting in hydroureter or hydronephrosis. Prenatally diagnosed tumors should be monitored closely for development of fetal hydrops.
Fetal magnetic resonance imaging is superior to ultrasonography in distinguishing solid tumor from hemorrhage. In addition, absence of acoustic shadowing by the pelvic bones permits accurate definition of cephalic extent and total dimension of the tumor, colon displacement, urinary tract dilatation, and intraspinal extent of a SCT. Such findings are important for surgical planning. 
Ninety percent of infants who have SCTs have a visible mass with a characteristic physical appearance over the sacrum at the time of delivery. The Altman Classification of the Surgical Section of the American Academy of Pediatrics classifies the tumors morphologically, according to their relative extent outside and inside the body, into four types (frequencies are indicated in parentheses):

1. Type I (45%): Predominantly external, projecting from the sacrococcygeal region and presenting with distortion of the buttocks
2. Type II (35%): Predominantly external, but have a large intrapelvic component
3. Type III (10%): Predominantly intrapelvic, with a small external buttock mass
4. Type IV (10%): Entirely internal, with no external or buttock component

 Type IV sacrococcygeal teratomas may occur as a familial form inherited in an autosomal dominant pattern. All of the four types may have an intraspinal component.
Most SCTs, even those that have an intrapelvic component, produce few or no functional symptoms. Large pelvic masses may create rectal or urinary tract compression. Neurologic deficits rarely are present in neonates. The physical examination always should include a rectal examination to evaluate any intrapelvic component. The most helpful imaging studies are plain anteroposterior and lateral radiographs of the pelvis and spine, looking for calcifications in the tumor and for spinal defects, and ultrasonography of the abdomen, pelvis, and spine. 
The recommended treatment is resection of the tumor en bloc with the coccyx in the first week after birth because long delays may be associated with a higher rate of malignancy. Histopathologic examination of SCTs shows the presence of a variety of parenchymal cell types representative of more than a single germ layer, usually all three (ectoderm, mesoderm, and endoderm), as described for the infant in the vignette. Neuroglial tissue, skin, respiratory and enteric epithelium, cartilage, smooth muscle, and striated muscle are the most common elements found. Bone, pancreatic tissue, choroid plexus, and adrenal tissues are identified less commonly. The degree of histologic immaturity is not of prognostic significance because immature tissue is considered normal in neonatal teratomas. The most common malignant component within a teratoma is a yolk sac tumor, also known as endodermal sinus tumor. 
The primary differential diagnosis of neonatal SCTs is meningocele. Typically, meningoceles occur cephalad to the sacrum and are covered by dura, but sometimes they are covered by skin. Physical examination reveals bulging of the fontanelle with gentle pressure on a sacral meningocele, which helps to establish the diagnosis before plain radiography, ultrasonography, and magnetic resonance imaging confirm it. The coexistence of meningocele with teratoma is recognized in the familial form of SCT, but these tumors usually are located presacrally. On histologic examination, meningoceles are characterized by the presence of fragments of spinal cord, glial cells, meningeal tissue, and nerves; glandular tissue is absent.
Other lesions in the differential diagnosis of neonatal sacrococcygeal masses include lymphangiomas, lipomas, rhabdomyosarcomas, and other malignant pediatric neoplasms. The presence of disorganized tissue originating from more than one germ cell layer is a hallmark of SCTs. Lipomas are comprised of mature adipose tissue, lymphangiomas of proliferating lymphatic channels, and rhabdomyosarcomas of rhabdomyoblasts in the absence of mature parenchymal cells from other germ layers.
Postpartum morbidity associated with SCTs is attributable to associated congenital anomalies, mass effects of the tumor, recurrence, and intraoperative and postoperative complications. Approximately 10% of SCTs are associated with other congenital anomalies, primarily defects of the hindgut and cloacal region. The recurrence rate varies between 7.5% and 22%.
Malignancy at birth is uncommon but increases with age and with incomplete resection.  Only 7% to 10% of tumors diagnosed before age 2 months are malignant. However, after 2 months, the incidence of malignancy rises to 66% in boys and 50% in girls. Malignancy generally is not believed to be a function of tumor size but is associated with the invasion of normal structures. Thus, type I lesions almost always are benign, and presacral (type IV) teratomas tend to be diagnosed at an older age and have an increased rate of malignancy. Most yolk sac tumors, the malignant component in SCTs, secrete AFP, which can be measured in the serum and demonstrated in the cells by immunohistochemistry. This marker is particularly useful for assessing the presence of residual or recurrent disease. AFP concentrations normally are very high in neonates and decrease with time. Therefore, high AFP values in the neonatal period have no prognostic significance but are important to assess completeness of tumor resection. The postoperative half-life is approximately 6 days.  Persistently high values after total resection of primary SCT together with the coccyx have been found to be a reliable marker of recurrence of poorly differentiated yolk sac tumors and may be an indication of the need for further surgical procedures or chemotherapy. 
All patients who have SCTs should be re-evaluated every 3 to 6 months for 3 years because there is a small but definite risk of malignant recurrence. The outpatient visit should include a thorough physical examination, including a rectal examination, and measurement of AFP.