From observation to aetiology: a case report of a twin fetus-in-fetu and a revisit of the known rarity

Abstract

A baby girl presented with an antenatal diagnosis of a retroperitoneal tumour. Postnatal imaging suggested that this mass contained two fetiform structures with spine and long bone formation. This teratomatous mass was completely excised at 3 weeks of age. Histology was consistent with twin fetuses-in-fetu, revealing two fetiform masses each with an umbilical cord connecting to a common placenta-like mass. Despite a difference in the weight of the twin fetuses-in-fetu, the level of organogenesis was identical and corresponded to fetuses of 10 weeks of gestation. Each mass had four limbs, intact skin, rib cage, intestines, anus, ambiguous genitalia, primitive brain tissue and a spine with ganglion cells in the cord. Although considered a mature teratoma in the current World Health Organization classification, the theory of formation from multiple pregnancies has been commonly implied in more recent literature. The true aetiology of this rare condition remains unclear.

Fetus in Fetu: Lessons Learned from a Large Multicenter Cohort Study

“…According to the most prevalent hypothesis, FIF is due to an embryological insult in a diamniotic monochorionic pregnancy with unequal division of the totipotent inner cell mass within the developing blastocyst which results in small cell mass within a maturing sister embryo, 2 as evidenced by the presence of vestigial remnants in the fetiform mass. This aforementioned insult leads to the partial abortion of one twin, which later becomes located as a parasitic twin inside the body of his own host twin.…”

“…9,10 The majority of cases clinically present during infancy, with the oldest report in a 47-year-old man. 2 In 70% of the reported cases, the main presenting complaint was an abdominal mass, of which 80% were predominantly retroperitoneal. 2 However, it may also be found in more uncommon sites, such as the oral cavity, sacrococcygeal region, and scrotum; other even rarer localizations, such as intracranial FIF, have also been reported.…”

“…2 In 70% of the reported cases, the main presenting complaint was an abdominal mass, of which 80% were predominantly retroperitoneal. 2 However, it may also be found in more uncommon sites, such as the oral cavity, sacrococcygeal region, and scrotum; other even rarer localizations, such as intracranial FIF, have also been reported. 11,12 There has been a great deal of dispute with regard to the embryologic origin of the lesion, particularly whether it is a well-organized and highly differentiated form of teratoma, or a distinctive entity.…”

Perinatal diagnosis and management of oropharyngeal fetus in fetu: A case report

“…1,2 The first case of fetus in fetu was reported in 1809 by Young. 1,2 The first case of fetus in fetu was reported in 1809 by Young.…”

“…Fetus in fetu is a rare congenital anomaly seen in approximately 1 in every 500 000 births with less than 200 cases reported in the literature worldwide. 1,2 The first case of fetus in fetu was reported in 1809 by Young. 3 The etiology is unknown, but the prevalent theory is that of a monozygotic, monochorionic, diamniotic twin gestation with the absorption of 1 twin.…”