Ultrasound Obstet Gynecol 2001; 18: 69 – 71
Ultrasound prenatal diagnosis of fetus in fetu
Blackwell Case Report Science, Ltd
P. MILLS, P. W. BORNICK, W. J. MORALES, M. ALLEN, E. GILBERT-BARNESS, P. K. JOHNSON and R. QUINTERO Florida Institute for Fetal Diagnosis and Therapy, St. Joseph’s Women’s Hospital, Tampa, Florida, USA
KEYWORDS: Aberrant fetus, Fetus in fetu, Prenatal diagnosis, Teratoma, Ultrasound
ABSTRACT A case of fetus in fetu was diagnosed prenatally using ultrasound. The differential diagnosis between a fetus in fetu and a highly differentiated teratoma is discussed. The importance of prenatal diagnosis of fetus in fetu and the effect on subsequent management are described.
INTRODUCTION In monozygotic twinning there are different twin types, depending on the developmental stage at which the twinning event occurs. Fetus in fetu (FIF) is a poorly understood and rare form of monozygotic twinning whereby an aberrant asymmetric twin becomes internalized in the other twin thus acting endoparasitically1. This latter point is still controversial as some believe FIF to represent a highly organized teratoma2. Since the condition was first described by Meckel in the late 18th century3, approximately 90 cases have been reported in the literature4. Most cases present as an abdominal mass during the first year of life, with only five cases being detected prenatally by ultrasound examination. The number of FIFs is usually single but multiples have been reported4. We present the findings in a case of FIF that was diagnosed prenatally and we discuss the differential diagnosis between a FIF and a highly differentiated teratoma. Furthermore, the importance of delineating these two diagnoses and the effect on subsequent management is discussed.
blood flow below the rudimentary spine and ventral portion of the mass. At this stage an endoparasitic FIF was diagnosed. The following day a girl of 38 gestational weeks was delivered by repeat elective Cesarean section. At delivery the baby had Apgar scores of 8 and 9 at 1 and 5 min, respectively, and had a full abdomen. Abdominal X-ray examination of the baby showed a 6 × 10-cm dense area in the central abdomen which created some slight mass effect. Within this mass, vertebrae, an overlapping cranium and ossified lower extremities could be delineated. Sonographic examination of the baby revealed in the midabdomen a soft tissue mass with internal calcification. Color Doppler investigation of the mass showed a rudimentary
CASE REPORT A 33-year-old pregnant woman, gravida 4 para 1, presented to our department following an abnormal ultrasound scan at 38 weeks’ gestation that revealed a fetal abdominal mass. Initially this was thought to be a meconium pseudocyst. However, upon detailed scanning in our department a 7-cm soft tissue abdominal mass with a rudimentary spine/femur/tibia and fibula was visualized (Figure 1). The mass was well circumscribed and power Doppler investigation revealed minimal
Figure 1 Prenatal ultrasound examination of the FIF at 38 weeks’ gestation. The FIF can be clearly seen within the fetus, with the skin of the fetus indicated by the large arrow and the vertebral column of the FIF by the small arrow.
Correspondence: Dr R. Quintero, 13601 Bruce B. Downs Blvd, Suite 160, Tampa, FL 33613, USA (e-mail:
[email protected]) Received 10-01-01, Revised 26-04-01, Accepted 1-05-01
CASE REPORT
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Prenatal diagnosis of fetus in fetu two-chamber beating heart with a rate of 108 beats per min (Figure 2a). Interestingly, when this rudimentary heart was visualized with Doppler techniques, it was possible to demonstrate collision in blood flow between the incoming neonatal blood and the intrinsic beating of the heart of the FIF (Figure 2b). A two-vessel cord was seen entering the mass which had a pulse of 131 beats per min in accordance with the host’s aortic pulsatility. The origin of these feeding vessels was traced to the celiac axis or the superior mesenteric artery. The exit vessel from the mass, with a pulse of 108 beats per min, was traced to the left renal vein. In addition, a hypoechoic triangular soft tissue structure was found anterior to the aorta measuring 12 × 10 mm in diameter. The origin of this mass was unknown. At laparotomy an encapsulated retroperitoneal mass was found below the mesocolon. The lobulated pink mass was eviscerated and found to be covered in skin although there were no recognizable features such as limbs or a face. A 1-cm section of umbilical cord was ligated. The second mass was 2.5 cm in diameter with a smaller umbilical cord-like structure. Both masses were surrounded by a membranous sac that appeared to represent an amnion. The surgeon opted against removal of this sac due to its close proximity to the duodenum, the mesenteric vessels, and the underlying great vessels. Postoperatively the baby required ventilatory assistance but this was stopped the following day with no further complications. Pathologically, the larger mass was found to be an acephalic fetiform mass with differentiation of all three germ layers present. Rudimentary upper and lower limbs were present with poorly developed digits. A rudimentary two-chambered heart was confirmed with an apparent venous component draining into a wrinkled atrium. An abdominal wall pedicle with a single artery was also identified. The smaller mass had both gross and microscopic evidence of highly differentiated skin and had a centrally located bone fragment resembling that of vertebrae. At 2 years of age the baby was admitted with an episode of intestinal obstruction. Work-up revealed an abdominal mass 10 cm in diameter. At laparotomy a mature cystic teratoma
Mills et al. was found and resected. On surgical pathology, the mass weighed 41.5 g and contained cheesy pink material and hair.
D ISCU SSIO N Since Meckel’s first report of a parasitic twin within its sibling there have been approximately 90 further reports of FIF in the medical literature3,4. Today there is much controversy concerning whether FIF requires a separate diagnosis or is just the highly differentiated end of the teratoma spectrum2,4. In 1935 Willis distinguished a FIF from a teratoma by the presence of an axial skeleton with limbs and organs arranged about this axis5. More recently Gonzalez-Crussi further defined FIF as, ‘any structure in which the fetal form is in a very high development of organogenesis’ and linked it ‘to the presence of a vertebral axis’6. This reflects Kim’s reverse definition of a teratoma as ‘an accumulation of pluripotential cells in which there is neither organogenesis nor vertebral segmentation’7. A recent review of all reported cases of FIF concluded that 91% of cases had a vertebral column, 82.5% had limbs, 55.8% had a central nervous system, 45% had a gastrointestinal tract and 40% had vessels4. In all cases the fetus was anencephalic and the lower limbs were more developed than the upper limbs4. Thus, the case we present and 82.5% of the reported cases of FIF fit either one or both of the definitions offered by Willis and Gonzalez-Crussi5,6. Numerous important clinical points are raised with the diagnosis of FIF. The initial presentation in the neonate of a full abdomen and diffuse calcifications in the abdomen on ultrasound offer differential diagnoses of FIF, meconium pseudocyst and teratoma8. As in this case, the main differentiating feature radiologically is that the calcification is organized in FIF and resembles bones. Furthermore, teratomas are more likely to occur in the sacrococcygeal, head, or neck regions9,10. Other features that were not present in this case such as pneumoperitoneum and ascites would be differentials for meconium pseudocyst and peritonitis1. Like all cases of FIF the diagnosis could not be confirmed until the pathologist had performed an
Figure 2 Doppler ultrasound examination of the baby soon after birth clearly demonstrates the presence of a rudimentary beating heart in the FIF (a). The collisional blood flow pattern between the incoming neonate’s blood (the upper waveform) and the intrinsic beating of the FIF’s rudimentary heart (the lower waveform) can be seen (b).
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Prenatal diagnosis of fetus in fetu examination. In this case the prenatal sonographic diagnosis of FIF was confirmed by the presence of highly ordered organogensis based around an axial vertebral column5,6. Furthermore, both masses were surrounded by a fluidcontaining sac with the larger of the two masses shown to have an umbilical cord composed of two vessels which took its blood supply from the superior mesenteric artery. These findings are consistent with those in most previous cases of FIF and further confirm the diagnosis4. A previous report by Patankar had advocated the use of computer tomography (CT) scanning to expound such detail to enable such a prospective diagnosis11. This case is clear proof that detailed ultrasound examination with power Doppler can supply such information to make a prospective diagnosis without the inherent risks associated with CT examination of the mother and child. The finding of a mature teratoma at 2 years of age raises important questions regarding the conceptual framework thus far described. Indeed, the association of a FIF plus a mature teratoma would suggest that both entities may indeed represent variations on a spectrum of a similar etiopathogenic process. Fetus in fetu may thus constitute the highest possible organized form of a mature teratoma, originating from omnipotent cells with a high capability of imitating embryonic development. In this sense, the current criteria for differentiating FIF from a mature teratoma would seem arbitrary and not necessarily reflective of different pathologic processes. Whether genetic information on the baby and the mass would be of help in this matter is yet to be determined. In conclusion, with advances in prenatal sonography the diagnosis of FIF, as shown in this case, can be made more confidently in the prenatal period. This will facilitate a planned birth of the child and immediate pediatric input. Following
Ultrasound in Obstetrics and Gynecology
Mills et al. confirmation of the diagnosis in the neonate, complete surgical excision should be performed and the excised FIF sent for detailed pathologic investigation including genetic testing. The latter may provide unambiguous evidence of a FIF but if not, then the degree of organogenesis present and its relationship to the axial vertebral column should be ascertained. If immature elements are found or there appears to be poor organization of the organogenesis, such as absent vertebrae, then the possibility of a well-developed teratoma with malignant potential should call for closer clinical, radiologic and serologic follow up.
REF ER ENC ES 1 Baldwin V. Pathology of multiple pregnancy. In: The Textbook of Fetal and Prenatal Pathology. Boston: Blackwell Science, 1991 2 Heifetz S, Alrebeeah A, Brown BS, Lau H. Fetus in fetu: a fetiform teratoma. Pediatr Pathol 1988; 8: 215– 26 3 Lee E. Fetus in Fetu. Arch Dis Child 1965; 40: 689– 93 4 Hoeffel C, Khoang Q, Tran T, Fornes P. Fetus in fetu: a case report and literature review. Pediatrics 2000; 105: 1335– 44 5 Willis R. The structure of teratoma. J Pathol Bacteriol 1935; 40: 1–36 6 Gonzalez-Crussi F. Extragonadal teratomas. Atlas of Tumor Pathology. Washington DC: Armed Forces Institute of Pathology, 1982 7 Kim O, Shinn K. Postnatal growth of fetus-in-fetu. Pediatr Radiol 1993; 23: 411– 2 8 Hing A, Corteville P, Ferrari M, Galli G, Zanetti G, Domini R. Fetus in fetu: molecular analysis of a fetiform mass. Am J Med Genet 1993; 47: 333– 41 9 Grosfeld J, Stepita D, Walter N. Fetus-in-fetu. Ann Surg 1974; 18: 80– 4 10 Goldstein I, Jakobi P, Groisman G, Itskovitz-Eldor J. Intracranial fetus-in-fetu. Am J Obstet Gynecol 1996; 175: 1389– 90 11 Patankar T, Fatterpekar G, Prasad S, Maniyar A, Mukerji S. Fetus in Fetu: CT appearance — report of two cases. Radiology 2000; 214: 735–7
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