Unusual presentation of fetus in fetu in triplet pregnancy mimicking abdominal wall defect

Introduction

Fetus in fetu (FIF) is a rare condition described by Meckel in 1800 with fewer than 200 cases reported in the literature [1]. It is thought to be a rare form of twinning in which an immature twin develops parasitically in the other twin. We reported a case of FIF located on the abdominal wall as an unusual presentation. Although FIF is always detected in twin pregnancies, to our knowledge this is the first case of FIF detected in a triplet pregnany.

Presentation of the case

A 35-year-old woman, gravida 2, para 1, was referred to our department at 31 weeks’ gestation with uterine contractions. Transabdominal ultrasound revealed 31 gestational weeks’ monochoryonic diamniotic twin fetuses, one of them with a 64×53 mm mass located on the abdominal wall with an umblical cord entering it and polyhydramniosis with a maximum amniotic fluid index and deep vertical index of 14 cm (Figure 1). Findings were well matched with the diagnosis of omphalocele containing liver. A cesarean section was performed due to active labor and breech presentation of the first fetus. The first fetus was 1320 g with an Apgar score of 8. The second fetus was 1470 g with a poor Apgar score of 2. The neonate was resuscitated and transferred to the neonatal intensive care unit. Postnatal clinical examination of the second fetus revealed a FIF located on the abdominal wall with upper and lower extremities extending cranially and caudally (Figure 2). There was no additional abnormality. The neonate expired 1 day after birth. An autopsy was not performed at the patient’s request.

Figure 1:

FIF with abdominal wall mass mimicking omphalocele and heterogeneous mass containing organized calcifications in the upper part of the image and a normal third fetus in the lower part of the image.

Figure 2:

Fetus with fetus in fetu located on the abdominal wall with upper and lower extremities extending cranially and caudally.

Discussion

FIF is due to defective embryogenesis at an early stage of development, with separation of a totipotent cell mass enclosed within a normally developing embryo. This cell mass gives rise to a malformed parasitic twin inside the body of an otherwise normally developing fetus [2]. Few cases of antenatal diagnosis have been published, and most of the cases are diagnosed after birth, most often in infants; however, the age of presentation varies from the antenatal period up to as old as 47 years [3, 4]. The location of the mass and its blood supply are variable. The most frequent location of a parasitic fetus is the retroperitoneal region, and uncommon sites are the oral cavity, sacrococcygeal region, scrotum, cranium, gastrointestinal tract, vessels, lungs, adrenal glands, spleen, lymph nodes and genitourinary system of the host twin [3, 5].

A FIF located on the abdominal wall mimicking omphalocele is a rare condition. The unusual location of a parasitic fetus is the leading cause of misdiagnosis of omphalocele in our case. Brand et al. reported diagnostic criterias such as a mass enclosed within a distinct sac, partially or completed covered by skin, grossly recognizable anatomic features and attached to the host by a pedicle containing a few relatively large blood vessels [6]. Our case did not fulfill the diagnostic criteria of FIF on sonographic examination. There is no general agreement on the definition of a FIF; most authors emphasize the need to find a vertebral column and limbs in the suspected intrafetal mass. Although limbs and a vertebral column were clearly seen on postnatal evaluation, a retrospective evaluation of sonographic views did not reveal these fetal structures clearly. A heterogeneous mass containing organized calcifications that was detected on retrospective sonographic views could be suggestive of FIF in our case (Figure 1). Similar to the present case, Khatib et al. reported a prenatally diagnosed case of FIF at 16 weeks’ gestation mimicing voluminous omphalocele seen at 12 weeks’ gestation [7]. Also, Fowler et al. described the features of a postnatally diagnosed case of split notocord syndrome, including the components of FIF. Giant omphalocele, duplicated colon and lower spine and a complex lumbosacral mass that was contiguous with an intraabdominal, retroperitoneally based “leg” encased within a saccular cecum were the major abnormalities, suggesting an etiologic relation between these entities and split notocord syndrome [8]. The extent of development of FIF is variable and appears to rely on the degree of vascular supply from the host. The vascular supply is usually a vascular pedicle originating from the abdominal aorta or other regional vessels. There has only been one case containing a functioning heart and no cases with a self-supporting circulatory system [9]. A clearly defined blood supply to the FIF could not be shown either with color Doppler flow or autopsy. FIF are commonly located retroperitoneally along the ventral midline in 80% of cases, and retroperitoneal teratoma is the most important differential diagnosis; FIF mimicking an abdominal wall defect is an unusual presentation [3, 10]. Although not definitive proof, a heterogeneous mass located on the abdominal wall with organized calcifications and without abdominal viscera (liver or bowel), nonvisualisation of cord insertion on mass convexity and absence of the umblical vein within the mass can be suggestive of FIF located on the abdominal wall. In conclusion, a FIF located on the abdominal wall is an unusual condition, and it should be kept in mind as one of the differential diagnoses of abdominal wall masses.