During my consultation with the patient I had the opportunity to discuss today’s unusual ultrasound findings via an Aramaic translator. The ultrasound features an intrauterine gestation at approximately 32 weeks gestation by biometric parameters and the patient’s stated LMP. The fetal abdominal circumference is enlarged due to the presence of an intraabdominal mass. Specifically, we noted within the fetus an intraabdominal solid mass measuring 7.1 x 5.4 x 6.4 cm. The mass is well encapsulated within a cyst surrounded by a hypoechoic rim of fluid. The mass within the fetal abdomen has the appearance of an early (albeit amorphous) gestational embryo. No fetal heart rate is noted, however there is Doppler flow present in what appears to be a rudimentary umbilical cord. There is a ring shaped mass with an echogenic border in the periphery of the mass which has the appearance of a yolk sac. The amorphous mass contains echogenic areas which are consistent with calcified tissue such as bone. The diameter of the amorphous mass measures consistent with a crown-rump length of 11 to 12 weeks. The overall appearance of this intraabdominal fetal finding suggests a condition known as fetus-in-fetu. The complete differential diagnosis would include:
- Fetus-in-fetu (likely)
- An intraabdominal teratoma (possible).
- Fetal volvulous (unlikely),
- Fetal bowel obstruction (very unlikely),
A fetus-in-fetu is an encapsulated, pedunculated vertebrate tumor. The tumor itself represents a malformed monozygotic, monochorionic diamniotic parasitic twin included in a host twin. Characteristically the fetus-in-fetu complex will be composed of an outer layer which is a fibrous membrane (equivalent to the chorioamniotic complex) that contains some fluid (equivalent to the amniotic fluid) and a fetus suspended by a cord or pedicle. The presence of rudimentary spinal architecture is used to differentiate a fetus-in-fetu from teratomas, which normally do not show evidence of spinal differentiation.
Prenatal diagnosis of fetus-in-fetu is unusual. The few cases detected prenatally generally present as a complex mass. The general appearance is a well-delineated capsule, with an echogenic mass suspended in fluid or partially surrounded by fluid. Occasionally, the diagnosis can be suggested by the recognition of a rudimentary spine.
As noted above, the next likely diagnosis on the differential diagnosis is that of a teratoma. Teratomas are disorganized congregations of pluripotential cells from all three primitive tissue layers. By differentiation and induction, they can achieve striking organization, with examples of several organs being well formed.
It should be noted that fetal teratomas have a malignant potential that has not been reported in fetus-in-fetu. Teratomas occur predominantly in the lower abdomen, not the upper retroperitoneum. In rare cases, both fetus-in-fetu and a teratoma will co-exist.
I have explained to the patient that a fetus-in-fetu or a intraabdominal teratoma would have to be evaluated for surgical resection in the neonatal period. Both of these conditions have been associated with the development of hydrops fetalis. Additionally, fetus-in-fetu has been described in conjunction with Trisomy 21. Our recommendations for this patient are as follows:
I have recommended that this patient undergo an amniocentesis to rule out the possibility of aneuploidy in this pregnancy since this would have a major impact on the neonatal management of this fetus.
Patient has agreed to return for the amniocentesis tomorrow.
I have scheduled a pediatric surgery consultation with Dr. Bhatia at Atlanta Pediatric Surgery Consultants. We will provide their office with a copy of our consultation and sonographic images at the time of this consultation which has been scheduled for Tuesday, April 19th, 2005.
We would recommend weekly fetal surveillance for the duration of this pregnancy in order to rule out the possibility of rupture of the mass or the evolution of hydrops fetalis.
