Fetus in fetu: a case report and review of the literature

Demystifying Fetus-in-fetu: A Systematic Review of Its Clinical and Pathological Attributes

Background

Fetus-in-fetu (FIF) is an exceedingly rare condition, characterized by a fetal-like or fetiform mass with a calcified vertebral axis surrounded by other organs or limbs. This systematic review was conducted to comprehensively analyze the clinicopathological attributes, management strategies, and prognosis of FIF to consolidate existing knowledge on FIF.

Methodology

Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, a comprehensive search was performed across various electronic databases, using the keywords "fetus-in-fetu," "fetus-ex-fetus," "homunculus," or "fetiform teratoma" to look for published articles until December 2023. Data extraction and analysis were carried out for cases meeting the defined criteria for FIF diagnosis, that is "presence of both/either the vertebral column and/or long bones of extremities" and "absence of immature elements."

Results

A total of 249 case reports/case series comprising 241 single FIF cases and 33 multiple FIF cases were included for analysis. The majority of single FIF cases presented within the 1st year of life, with a slight male predominance. Retroperitoneal location was most common, and imaging modalities played a crucial role in preoperative diagnosis. Complete surgical removal of the mass with detailed histopathological examination is the cornerstone of treatment for FIF, with favorable outcomes in the majority of cases. Both mature and immature teratoma can rarely be found in association with FIF.

Conclusion

This comprehensive systematic review enhances understanding of FIF, emphasizing the importance of accurate diagnosis by diligent histopathological examination, appropriate management, and vigilant postoperative monitoring for favorable outcomes.

Antenatally detected fetus in fetu case report

Fetus in fetu (FIF) is an extremely rare pathology in which a malformed fetus is located in the body of its twin. It may occur as a result of an aberration of the twinning process. It is important to distinguish this condition from a teratoma. This article emphasizes the importance of the various modalities in the antenatal diagnosis and post natal follow up of FIF. An appropriate early intervention if instituted results in a good prognosis. Only few cases of FIF have been reported in medical literature. We present a case which was antenatally diagnosed and proven on histopathology postnatally. This case report illustrates the importance of multimodality imaging techniques in the diagnosis of this condition.

Fetus-in-fetu: a pediatric rarity

Fetus-in-fetu (FIF) is a rare entity resulting from abnormal embryogenesis in diamniotic monochorionic twins, being first described by Johann Friedrich Meckel (1800s). This occurs when a vertebrate fetus is enclosed in a normally growing fetus. Clinical manifestations vary. Detection is most often in infancy, the oldest reported age being 47. We report the case of a 4-day-old girl who was referred postnatally following a prenatal fetal scan which had revealed the presence of a multi-loculated retroperitoneal mass lesion with calcifications within. A provisional radiological diagnosis of FIF was made. Elective laparotomy revealed a well encapsulated retroperitoneal mass containing among other structures a skull vault and rudimentary limb buds. Recovery was uneventful. Here we discuss the difference between FIF and teratomas, risks of non-operative therapy and the role of serology in surveillance and detection of malignant change.

[Fetus in fetu: a case report]

Fetus in fetu is an abnormality secondary to abnormal embryogenesis in a diamniotic, monochorionic pregnancy. It is a rare pathological condition and fewer than 100 cases have been reported in the literature. We report a neonatal case which occurred in a girl who had been hospitalized since birth because of an abdominal mass. A conventional radiograph of the abdomen revealed a right mass containing calcifications, which displaced intestinal structures to the left. Abdominal ultrasonography and CT scan revealed a vascular and heterogeneous mass that contained numerous calcifications. The diagnosis of teratoma was suspected. After surgical excision, macroscopic and pathologic examination confirmed the diagnosis of FIF.

Fetus in Fetu

Fetus in fetu is a congenital abnormality in which a nonviable, parasitic fetus grows within its twin. It is a rare cause of retroperitoneal abdominal mass in infants and children. The authors report a recent case of a six-month-old girl who presented with unexplained abdominal distention. A sonogram and a magnetic resonance imaging examination showed a multiloculated, complex cystic mass with calcified and soft tissue components. A definitive diagnosis and discrimination from a teratoma was difficult to make because of the absence of a distinctive criterion, the presence of a vertebral column. Pathologic examination showed a complex mass consisting of well-formed bowel and upper respiratory tract segments as well as mature neuroglial tissue, skeletal muscle tissue fibers, and bone tissue that contained bone marrow, supporting the diagnosis of fetus in fetu. Therefore, the nonvisualization of a vertebral column on imaging should not exclude fetus in fetu from the differential diagnosis.

Fetus-in-fetu: report of a case and a review of the literature

A 2-week-old girl was found to have an asymptomatic abdominal mass on routine examination. Surgical removal revealed the mass to have 4 limb buds situated relative to a palpable vertebral column. Karyotyping revealed the mass to be 46 XX. The mass was therefore diagnosed as a case of fetus-in-fetu. The literature on this rare entity is reviewed, and the diagnosis and pathogenesis of the disease are discussed.

Fetus in fetu--from prenatal ultrasound and MRI diagnosis to postnatal confirmation

We report a case of fetus in fetu presented as a complex intra-abdominal heterogeneous cystic lesion during ultrasound examination of the fetus at 25 weeks of gestation. Progressive growth of this mass was noted in the prenatal period. Fetal magnetic resonance imaging provided additional information to aid in the prenatal diagnosis. This allows proper counselling for the parents and helps to plan the postnatal management. Surgical excision was carried out in the early neonatal period and the diagnosis of fetus in fetu was confirmed.

A neonate with cleft palate and a fetal mass in the oral cavity: a rare case of an oral fetus-in-fetu

Fetus-in-fetu is a rare congenital condition in which a malformed fetus-like structure is found in the body of its twin. We report a unique case of a male neonate with cleft palate and a fetus-like structure arising in his oral cavity. The neonate underwent emergent surgical removal of the mass immediately after delivery. Radiological and pathological studies of the resected mass provided supportive evidence for the case of an oral fetus-in-fetu. To our knowledge, there are few cases of oral fetus-in-fetu in the literature. Moreover, the presence of cleft palate in this neonate is of potential interest and clinical importance.

Fetus in fetu and fetaform teratoma in 2 neonates: an embryologic spectrum?

OBJECTIVE

The purpose of this study was to describe the imaging and pathologic findings of 2 cases of complex neonatal abdominal masses and to discuss the probable common embryologic etiology of fetus in fetu (FIF) and fetaform teratomas.

METHODS

Two male neonates had complex cystic abdominal masses, 1 of which was diagnosed prenatally, and both had abdominal sonography. One patient also had abdominal computed tomography. Both patients subsequently underwent surgical resection, with pathologic and genetic analysis of these masses.

RESULTS

One patient had typical imaging, pathologic, and genetic findings of FIF. The second patient had a well-formed mass that was diagnosed pathologically as a teratoma yet had most of the criteria for FIF that have been set forth in recent embryologic literature.

CONCLUSIONS

Recent concepts regarding the origin of FIF suggest that it is part of a spectrum of monozygotic twinning gone awry, ranging from conjoined twins at one end to fetaform teratomas at the other. The imaging and pathologic features of these 2 cases serve to reinforce this concept.

Fetus in fetu--diagnostic criteria and differential diagnosis--a case report and literature review

Fetus-in-fetu (FIF) is a rare congenital condition in which a vertebrate fetus is incorporated within its twin. The authors report the case of a newborn boy with prenatal ultrasonographic diagnosis of intraabdominal mass, provoking compression of the left kidney. Plain abdominal radiography, ultrasonography, and computer tomography showed a cystic mass containing multiple calcifications. Pathologic examination showed an irregular fetiforme mass, weighing 8 g, attached to an amniotic sac by a rudimentary umbilical cord with 2 rudimentary limbs, vertebral bodies, encephalus, coroidal plexus, stomach, duodenum, bowel, adrenal glands, upper and lower respiratory tissue, spleen, lymphoid tissue, single cavity heart, and kidney. Molecular analysis using an informative genetic marker, for uniparental isodisomy of chromosomes 14 and 15 showed no genetic difference between the host infant and the fetiform mass. Serum alpha-fetoprotein was < or = 16.000 UI/mL (reference values for age, 4 to 18.9904 UI/mL) before surgery and 8.364 UI/mL after surgery.

Epignathus: always a simple teratoma? Report of an exceptional case with two additional fetiforme bodies

We report on a case of a fetal epignathus combined with two fetus-like structures resembling acardius acranius. The anomaly was detected at 23 weeks of gestation and led to termination of pregnancy at 24 weeks. This is the first description of epignathus with parasitic fetuses detected prenatally. It shows that the boundary between fetal teratoma and multiple pregnancy in special cases may be difficult to define.

Parasitic conjoined twins: external, internal (fetuses in fetu and teratomas), and detached (acardiacs)

During the course of researching the embryologic etiology of conjoined twins, more than 1260 individual cases were collected from the literature and the reported abnormal anatomy tabulated and evaluated in the light of known embryology. It soon became apparent that the association of conjoined twins and their parasites with fetuses in fetu, acardiacs, and teratomas was more frequent than could be attributed to chance. These anomalous fetuses form a continuum, strongly suggesting that they are all variations of abnormal conjoined twinning, with the site of union and the extent of damage (or defect) of one embryo resulting in (1) an externally attached parasitic twin, (2) an enclosed fetus in fetu, (3) an internal teratoma, or (4) an acardiac connected via the placenta. Common patterns among them are a family history of twinning, the predominance of females, and the frequent presence of a twin or triplet accompanying the malformation. The several reports of chromosomal abnormality suggest that perhaps, at least on occasion, it is a genetically imperfect embryo that develops into a defective fetus. Of singular importance is the fact that rarely, if ever, is either a functional heart or a competent brain found in any of these abnormal fetuses, suggesting that the etiology of all of them is a primary cardiac malformation with secondary disruption in the development of the brain.

Fetus in fetu. Rare cause of a lump in an adult's abdomen

Fetus in fetu is a rare entity. The patient usually presents in childhood. A case in which the patient presented in adulthood, with a lump in the abdomen, is reported. Computed tomography findings were diagnostic of this condition and a prospective diagnosis could be made. Computed tomography also helped to differentiate it from mature teratoma.

Intrahepatic fetus-in-fetu: a case report and review of the literature

The authors report the third case since 1964 of fetus-in-fetu presenting at Red Cross Children's Hospital. A fetal liver abnormality was detected during routine antenatal ultrasound scan, and the postnatal diagnosis of an intrahepatic, multiple fetus-in-fetu was made with abdominal ultrasound scan, plain radiograph of the abdomen and computed tomography. The mass was removed surgically by hemihepatectomy when the patient was 4 months of age. Imaging and the macroscopic and microscopic appearances of the abnormality confirmed the diagnosis and amplified it to include an adjacent teratoma. Multiple small subcapsular and perimass vascular hamartomas were coincidentally discovered in the liver. Two of the 3 nodules within the amniotic-lined cavity of the intrahepatic mass individually comply with the accepted criteria for fetus-in-fetu, and the third nodule has the accepted features of a benign teratoma. The existence of multiple fetus-in-fetu and fetus-in-fetu combined with a teratoma, is recorded in the medical literature. The imaging as well as the macroscopic and microscopic features are illustrated.

Fetus-in-fetu: a case report and review of the literature

A unique case of intraperitoneal fetus-in-fetu attached to an ovary is presented. An asymptomatic newborn girl was found to have a mobile cystic mass in right side of her abdomen. Radiological investigations showed fetus-in-fetu. During laparotomy, an intraperitoneal fetus-in-fetu was found attached to right ovary and vascular pedicle to ovarian vessels. Only 79 cases of fetus-in-fetu have been reported, and this is the first such case attached to an ovary.

Fetus-in-fetu with malignant recurrence

Fetus-in-fetu is an unusual condition in which a vertebrate fetus is enclosed within the abdomen of another fetus. These occurrences are usually benign. This report describes an instance of malignant recurrence after resection of a fetus-in-fetu.

Highly differentiated teratoma and fetus-in-fetu: a single pathology?

A case of sacrococcygeal teratoma is presented with characteristics of fetus-in-fetu. This pseudo-fetus presented a rudimentary single cavity heart, which beat at a different rate to that of the affected infant. X-ray examination showed no spinal column. This case confirms that fetus in fetu can be a remarkably complex, well-differentiated, highly organized teratoma.

Double fetus in fetu: diagnostic imaging

Fetus in fetu is a rare pathological condition, presenting as a congenital tumor. It consists of a malformed parasitic twin that is found within the body of its sibling. Less than 70 cases have been reported and in most of them a definite diagnosis was only made during surgery. We present a case with two fetuses in the retroperitoneum and describe the criteria to be kept in mind for a correct preoperative diagnosis using the current imaging modalities.

Enteric nervous system and endocrine cells demonstrated in the gut in teratomas

A case of retroperitoneal teratoma, showing considerable morphological development presented as an encapsulated and pedunculated tumour with a seemingly mature intestinal loop. Markedly complex intramural nerve plexuses and numerous epithelial endocrine cells were revealed immunohistochemically in the gut tissue. Ten other mature teratomas containing gastrointestinal tissues were examined for comparison, but neither intramural ganglia nor nervous networks were found in the gut components, despite the presence of amine- and/or peptide-containing endocrine cells in all intestinal mucosa linings. Enteric endocrine cells were found to occur irrespective of the differentiation of intestinal layers or the occurrence of neural elements. These findings suggest that the epithelial endocrine cells of intestinal mucosa do not have the same origin as enteric neurons, but are rather of endodermal origin. This invertebrate well-formed teratoma, containing a highly organized enteric nervous system, suggests that teratoma and fetus in fetus are related entities distinguished by the presence of a vertebral axis.

Postnatal growth of fetus-in-fetu

A 6-month-old-boy who presented with an abdominal mass disclosed a well-formed fetus in the retroperitoneum. This mass was retrospectively noted at the age of 1 month. Comparison of two radiographic examinations done 5 month apart clearly demonstrated the enlargement of an included fetus in the bearer's abdomen. Our report of this rare condition focuses on the growth of the fetus-in-fetu detected by roentgenograms.

Fetus in fetu or giant epignathus protruding from the mouth

A huge and extremely organoid mass, protruding from the mouth of a newborn and causing respiratory embarrassment, was resected. It was difficult to make a clear distinction whether this mass was fetus in fetu or a highly organoid epignathus dealing with the findings obtained from its gross and histological examination of the mass.

Mature sacrococcygeal teratoma containing the lower half of a human body

Twins were diagnosed by ultrasound in a 29-year-old woman. The cesarean delivery revealed at first a mature girl with a large benign sacrococcygeal teratoma and then a healthy boy. X-ray and CT examinations of the teratoma showed pelvic and lower limb bones. A mature teratoma-tridermoma (weight 475 g) containing the underdeveloped lower half of a human body was confirmed during surgery and verified morphologically. The fraternal twins, i.e., the girl operated upon and her brother, have been followed for 5 years and are without any complaints. They have normal neurological function.