Case Study: Diagnosing Sacrococcygeal Teratoma

July 3, 2014

After a discrepancy between gestational age and fundal height, an ultrasound exam revealed one of the most common congenital tumors deriving from germ cells.

A 35-year-old woman presented at 23 weeks’ gestation for a routine transabdominal ultrasound to exclude any congenital fetal anomalies. This was her first pregnancy, and she had not undergone any previous ultrasound scans. To date, her pregnancy has been uneventful.

Prior to this pregnancy, the woman’s menstrual cycles had been normal, and she has had no history of any major illnesses. The patient has had amenorrhea since becoming pregnant and has had no vaginal discharge or bleeding during the pregnancy.

Clinical examination: All vital signs were within normal limits, including blood pressure, which was 124/82 mm Hg. Her chest examination was normal as well. The abdominal examination revealed a fundal height that corresponded to a gestational age of 25 weeks, which exceeded the expected fundal height for a 23-week pregnancy.

Imaging studies: The ultrasound images from this routine exam are shown below. (All images in this case are courtesy of Firoz Bhuvar, MD.) 

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What are your findings based on these two images?

Sonographic Findings

The first image (Figure 1) shows a sagittal section of the fetal abdomen and lumbosacral spine with an obvious abnormality. The fetal abdomen appears normal in size and shape. However, the fetal bladder is not visualized well. The most obvious anomaly is the huge structure (mass) that is seen towards the caudal end of the fetus, prompting the questions: What is its relation to the fetal urinary bladder? Or is it part of the fetal pelvis or arising from the pelvis?

Let’s consider the mass is part of the fetal urinary bladder. The most common bladder anomaly is an overdistended urinary bladder, which could result from megacystis. If megacystis, this lesion would extend anteriorly from the pelvis. The structure seen here is a huge, primarily cystic, mass extending from the caudal end of the fetus both anteriorly and posteriorly as well as laterally to both sides. The mass is well-defined, has thick walls with shaggy internal margins, and contains particulate fluid. There are also some solid nodules within the mass. This might be a urachal cyst-a known fetal anomaly-but a urachal cyst would present along the anterior abdominal wall. This definitely is not the case here, which excludes this diagnosis.

The most common lesion arising from the caudal end of the fetus that is associated with the sacral spine and that can present as a complex cystic mass is a meningocele. A meningocele can fit the description above. Meningoceles generally arise from the lumbosacral region and usually are dorsal in location. However, a myelomeningocele or a meningocele usually isn’t seen in the location of the lesion in this fetus-the sacrococcygeal region-and a meningocele is a thin-walled sac with fluid collection located at the upper lumbosacral spine. As stated previously, the lesion in question is cystic with thick shaggy walls and with some solid tissue. These features safely exclude a diagnosis of meningocele.

Other diagnostic possibilities could include a sacrococcygeal teratoma, which is a mass that is usually complex and solid in nature but that can also be cystic and grow to be quite large. The lesion here seems to fit this diagnosis; it’s huge, and although cystic, it has solid tissue with echogenic matter within it. As said earlier, a sacrococcygeal teratoma arises from the distal end of the sacrum and the coccyx. This definitely is the case here. More images may help confirm this diagnosis.

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These 3-D ultrasound images (Figure 3 and Figure 4) confirm a diagnosis of sacrococcygeal teratoma, which fits all of the findings:

- A huge complex mass containing both cystic and solid tissue.

- The location-the distal sacrum and coccyx of the fetus.

- Shaggy irregular but well-defined walls of the mass.

- Extension of the mass below the fetus in all directions.

- A fundal height/uterine size that is larger than expected for the pregnancy.

- Mild polyhydramnios.

Final diagnosis: Sacrococcygeal teratoma

Discussion

A uterus that is larger than expected for the corresponding gestational age is often the first clinical clue that either the fetus or something else within the uterus needs a closer look. This clinical sign is often the first indication of a sacrococcygeal teratoma. It is the most common congenital tumor and is known to grow so large that it can threaten the life of the fetus.

Although usually solid with cystic components, a sacrococcygeal teratoma can also present as a primarily cystic lesion with solid components, as in our case. It is composed of all three germ cell layers of the fetus, namely the ectoderm, endoderm, and the mesoderm. They are thought to arise from the totipotent cells of the early embryo and can occur as early as the first trimester. With the widespread use of ultrasound, it is now possible to diagnose sacrococcygeal teratoma in the early stages. The lesion also is often associated with polyhydramnios.

Differential diagnosis

The differential diagnoses for sacrococcygeal teratoma include meningocele, myelomeningocele, megacystis, and even extrarenal tumors, such as Wilms' tumur and neuroblastoma. As previously mentioned, these can be excluded on the basis of both clinical and ultrasound findings.

Prognosis

The prognosis for sacrococcygeal teratoma diagnosed in intrauterine life is poor, with a mortality rate of as high as 50%. The mortality rate for sacrococcygeal teratoma diagnosed in neonatal life is comparatively less. Thus, careful monitoring of the fetus and mother are essential during fetal development to prevent complications such as oligohydramnios and polyhydramnios as well as fetal hydrops.

References:

1. Antony J. Ultrasound image gallery website. Available at: http://www.ultrasound-images.com. Accessed June 27, 2014.

2. Swayze CF, Wheeler TC. Sacrococcygeal teratoma. Available at: http://sonoworld.com/fetus/page.aspx?id=530. Accessed June 27, 2014.

3. Sacrococcygeal teratoma/SCT. .Available at: http://www.cincinnatichildrens.org/service/f/fetal-care/conditions/sct/default/. Accessed June 27, 2014.

4. Rumack CM, Wilson SR, Charboneau JW, Levine D, eds. Diagnostic Ultrasound. 4th ed. Philadelphia: Mosby; 2011.