Origin and mechanisms of formation of fetus-in-fetu: two cases with genotype and methylation analyses

Infantile fetiform abdominal mass: Teratoma or fetus in fetu? A case report with insights into radiological diagnosis and surgical management

Fetus-in-fetu (FIF) is a rare congenital anomaly in which a malformed parasitic twin develops within the body of a live fetus or child. Abdominal teratoma, a type of germ cell tumor, can be a great imaging mimicker of FIF and vice-versa, as they both can present as a heterogeneous mass with calcifications and a fat component. Radiological differentiation of these 2 entities should be made because of the difference in surgical planning and treatment options. Features such as visualization of distinct bony vertebral elements and encysted cystic components are the specific features of Fetus in fetu [1]. In contrast, the presence of elevated serum markers can help diagnose teratoma. Here, we report a case of a 5-month-old girl presented with progressive distension of the upper abdomen for the last 2 months, noticed by her mother. Her initial imaging with abdominal X-ray and ultrasonography showed the presence of a large heterogenous solid-cystic mass in the upper abdomen with large elongated calcifications. A provisional diagnosis of teratoma vs FIF was considered. CECT abdomen showed clear identification of osseous structures of the axial and appendicular skeleton within a fat density mass, along with an encapsulated cystic component, strongly suggestive of FIF. Her serum tumor markers were within normal limits. The final diagnosis of FIF was confirmed on Laparotomy and postoperative specimens.

Fetus in Fetu: A Rare Congenital Anomaly Diagnosed Postnatally by Ultrasonography and MRI

Fetus in fetu (FIF) is a rare congenital anomaly with two controversial theories regarding its embryogenesis. Although it is an extremely rare condition, it should be kept in mind as a differential diagnosis while evaluating children with abdominal calcification. Radiological findings on postnatal days 2 and 5 of a neonate with an antenatal scan showing an abdominal mass in the fetus are described here. Ultrasonography and magnetic resonance imaging (MRI) revealed the mass in which the contents favored a diagnosis of the FIF. Characteristic features of FIF on MRI have been less explored and knowledge regarding the same will be of immense help to the radiologist. Complete surgical excision followed by histopathology confirmed the diagnosis.

Case Report: The Medical and Surgical Management of an Infant With Extreme Prematurity and Fetus-In-Fetu

Fetus-in-fetu (FIF) is a rare congenital anomaly where a parasitic twin is within the body of a host twin. FIF is reported to occur in 1:500,000 live births. Herein, we report the first case of the medical and surgical treatment of a FIF patient who was born with extreme prematurity at 25-weeks gestation. With the multi-disciplinary coordination of neonatology, surgery, and interventional radiology, the patient was able to achieve a window of medical stability 4 weeks after birth. A decision was made at that time to proceed with an intra-abdominal and perineal resection of the FIF. The FIF was successfully resected and the patient was able to recover from the operation, with eventual discharge from the NICU. In conclusion, extreme prematurity and FIF may be amenable to surgical resection and a multi-disciplinary approach is crucial to achieve the desired outcome.

Placenta Teratoma or Acardiac Fetus Amorphous: A Case Study by DNA Genotyping

To date, 40 cases of placental teratoma and 21 cases of umbilical cord teratoma have been reported in the literature. Such entities are purportedly described as originating from ectopically derived totipotential germ cells forming 1 or more of 3 germ layers, similar to teratomas arising in other sites. These entities have been described as distinct from acardiac twins based on the absence of both an axial skeleton and/or separate umbilical cord attachment. We present a case that would be compatible with placental teratoma according to these criteria. However, DNA genotyping analysis of the "teratoma" and its corresponding normal placental tissue revealed an identical genetic profile at all microsatellite polymorphic loci with exception of one locus demonstrating loss of heterozygosity involving 1 of 2 "teratoma" samples tested. Our finding established that the "teratoma" in fact represented a monozygotic acardiac (amorphous) twin with aberrant division of embryogenesis as a continuum of the monozygotic twinning phenomenon. In summary, this is the first case study of so-called placental teratoma by DNA genotyping investigation. We conclude that the diagnostic term "placental teratoma" should be discouraged unless evidence of monozygotic twining can be ruled out by molecular genotyping.

A rare case of fetus in fetu in the sacrococcygeal region: CT and MRI findings

BACKGROUND

Fetus in fetu is a rare condition in which a malformed fetus is found in the body of a living twin. The retroperitoneum is the most common location of this condition. However, the sacrococcygeal region is a rare site of the disease. The presence of vertebral bodies and limbs differentiates FIF from teratoma. Imaging modalities are important for diagnosing FIF.

CASE PRESENTATION

A 12-months old boy was hospitalized because of a mass in the sacrococcygeal region. CT showed a large, complex mass with bony structure resembling sacrococcygeal bone, hip bone and the femur in the sacrococcygeal region of the boy. The blood supply of the mass was from the aorta of the host. MRI revealed the mass was connected with the dilated sacral canal of the host, which resulted in tethered cord. A preoperative diagnosis of FIF was made and surgery was performed to remove the mass. Surgical removal and subsequent pathological examination revealed the anencephalic fetus had limb buds and a sacrum but no axial skeleton, which supported the diagnosis of FIF. Conclusions CT and MRI played important roles in diagnosing FIF based on the location of the lesion.

Fetus-in-Fetu: A Case of Ovarian Involvement and Residual Regrowth in a Teenager

BACKGROUND

Fetus-in-fetu (FIF) is a rare, congenital soft tissue mass typically occurring retroperitoneally in neonates younger than 18 months. We present a 13-year-old girl with an ovarian FIF occurrence and subsequent residual regrowth after resection.

CASE

A 13-year-old girl presented with abdominal pain and was found to have a 19-cm, complex, right adnexal mass. Preoperative tumor markers were normal and risk assessment favored a benign process. She underwent open ovarian cystectomy with pathology showing FIF. Nine months later, she had a recurrence of her ovarian mass and underwent right oophorectomy, with FIF on pathology.

SUMMARY AND CONCLUSION

In patients in whom FIF is discovered within the ovary, consider postoperative surveillance, because of the risk of recurrence or residual disease.

Fetus in Fetu in an Adult Female and Brief Review of Literature

Fetus in fetu (FIF) is a very rare condition in which malformed fetus is found within the body of a living twin, most commonly within the retroperitoneum. It is a parasitic fetal twin of a diamniotic, monozygotic type. It should be differentiated from teratoma by the presence of organized vertebral column and appropriately arranged other organs or limbs around it. There is no such axial arrangement in teratoma, which has also got definite malignant potential. We report a case of FIF in a 21-year-old lady who presented late with nonspecific abdominal symptoms. Preoperative diagnosis of FIF in this case was made on computed tomography, and the patient underwent exploratory laparotomy with complete excision of mass. The excised mass in a sac was proven to be FIF on the basis of gross and histopathological examination. Surgical excision is the ideal treatment even teratoma being the differential diagnosis.

First Case Report of Adnexal Fetus in Fetu

BACKGROUND

There is an ambiguous and controversial line between fetiform teratoma and fetus in fetu (FIF) as differential diagnoses of a fetiform mass. Classically, the presence of vertebral column often with a relatively proper arrangement of other organs around the central axis favor the diagnosis of FIF over teratoma.

CASE

Based on previously proposed criteria and the presence of vertebral organization in the radiological and histopathological assessment of the fetiform mass, we present an extremely rare case of adnexal FIF in a 10-year-old girl presenting with acute abdominal pain.

SUMMARY AND CONCLUSION

Whether FIF and fetiform teratoma are one entity or two, clinical discrimination for the choice of treatment seems to be unnecessary and the patient should be clinically followed for the probable malignant potential.

Preoperative diagnosis of a "humanoid" fetus in fetu using multimode ultrasound: a case report

Background

Fetus in fetu (FIF) is a rare congenital anomaly. The preoperative diagnosis of FIF and differentiating it from teratoma and other abdominal tumors can be challenging for radiologists. Clarification of the blood supply and the relationship with the surrounding vessels is especially helpful for successful surgery; however, multimode ultrasound (US) performed for FIF has rarely been explored. Here, we first report a “humanoid” FIF case diagnosed by multimode US examinations, with the use of contrast-enhanced ultrasound (CEUS) for clarifying the blood supply features.

Case presentation

A 25-day-old preterm male infant was referred to our hospital for surgery. The US and computed tomography (CT) examinations led to a diagnosis of teratoma at the local hospital. The laboratory workup at our hospital revealed an elevation of total bilirubin, direct bilirubin, indirect bilirubin, alpha-fetoprotein, and neuron-specific enolase levels. A precise diagnosis and differentiation from teratoma, hepatoblastoma, neuroblastoma and other abdominal tumors were needed. In addition, the blood supply and the relationship with the surrounding vessels needed clarification prior to surgery. Multimode US examinations were performed and the features of a “humanoid” FIF as well as the blood supply for the abdominal lesion of the infant were suggested by grayscale US, color Doppler flow imaging (CDFI), and CEUS. Furthermore, CDFI and CEUS revealed an aorta-like structure and umbilical cord-like blood vessels in the “humanoid” FIF, and the CEUS helped with marking the surface of the infant’s abdominal wall. To the best of our knowledge, this is the first case report of CEUS in FIF, and the blood supply was clearly demonstrated in the FIF. The intraoperative findings confirmed our multimode US findings and revealed a “humanoid” FIF. The infant quickly recovered after the operation and had no positive findings at the 2-year follow-up visit.

Conclusions

Multimode US was helpful in diagnosing the rare FIF without radiation exposure. Specifically, CEUS clearly demonstrated the limb branch vessel-like structures, the abdominal aorta-like structure and the blood supply, which was useful for the FIF diagnosis and for avoiding damage to important vessels during the operation.

Fetus in fetu - a rare developmental anomaly

Fetus in fetu is a rare condition which most often presents as a fetiform calcified mass in the abdomen of its host, fetus or newborn. We report a case of 8-month-old girl with history of abdominal distension. Ultrasonography and computed tomography scan revealed a mass in which the contents favor a fetus in fetu rather than a teratoma. She underwent surgery and the mass was resected in toto. Radiograph of the resected specimen showed the presence of rudimentary vertebral column which was later confirmed by pathologist.

Intracranial fetus-in-fetu with numerous fully developed organs

Fetus in fetu (FIF) is an extremely rare anomaly featuring a monozygotic, diamniotic, parasitic twin, enclosed within its host twin. It is characterized by the presence of vertebrae and well-developed organs in a fetiform mass. Only 18 cases of intracranial FIF have been published. Of them, only five cases were prenatally detected. This study prenatally demonstrated triplet FIFs at 31 weeks within amniotic-like sac in the fetal skull, consisting of multiple well-defined organs. The FIF attached to the host twin via body stalk containing a single main feeding artery and vein, representing umbilical vessels. Surgical removal was performed at the age of two months. Pathological examination showed the triplet FIF, consisting of numerous well-developed organs (musculocutaneous-skeletal, nervous, respiratory, gastrointestinal systems etc.), with soft tissue/skin coverings, but no vertebral body was seen. Molecular genetic analysis revealed identical genetic mapping among the three FIFs and the host. This case provides strong evidence against Willis's hypothesis but supports Spencer's theory of abnormal twinning.

Fetiform teratoma was a parthenogenetic tumor arising from a mature ovum

The aim of this study was to investigate the parthenogenetic origin of fetiform teratoma by using molecular genetic studies and methylation status analyses. A fetiform teratoma was removed from a 35-year-old nulligravida woman. Genotyping of microsatellite marker loci, microarray analysis of single-nucleotide polymorphism (SNP) loci and methylation status analysis of the differentially methylated region (DMR) within the human IGF2-H19 locus were performed. Karyotypes of the host and the fetiform teratoma were 46, XX. The fetiform teratoma was homozygous at all loci and meiotic recombinations in the tumor were confirmed by SNP microarray analysis. Methylation analysis indicated that the host had both methylated and unmethylated IGF2-H19 DMR alleles, while the fetiform teratoma had unmethylated alleles only. Genetically, the fetiform teratoma had homozygous genotypes with meiotic recombination and a duplicated unmethylated host allele, indicating that it was a parthenogenetic tumor arising from a mature ovum after meiosis II. This is the first demonstration of a fetiform teratoma originating from a mature haploid ovum.

Fetus in Fetu: Case Report and Brief Review of Literature on Embryologic Origin, Clinical Presentation, Imaging and Differential Diagnosis

BACKGROUND

Fetus in fetu (FIF) is a rare entity in which a malformed diamniotic monochorionic parasitic fetal twin develops inside a normal co-twin's body, most commonly in the abdominal cavity. FIF is differentiated from the teratoma by the presence of vertebral column often with an appropriate arrangement of other organs or limbs around it.

CASE REPORT

A two-and-a-half-year-old girl presented with a painless abdominal swelling in the right hypochondrium. On imaging, a heterogenous soft tissue mass with internal calcific densities was noted in the retroperitoneum. The mass had vertebral organization, limb and pelvic bones. The presence of a fetiform teratoma was suspected and surgery revealed an encapsulated mass with an anencephalic head, spine, upper and lower limb buds. Histopathology confirmed the presence of a fetus in fetu. The postoperative period was uneventful with no evidence of recurrence.

CONCLUSIONS

FIF is a pediatric rarity. Cross-sectional imaging helps in differentiating it from a teratoma, meconium peritonitis and abdominal ectopic pregnancy. Surgical excision is the treatment of choice for this benign condition, which requires a follow-up only in certain cases. This case report describes a retroperitoneal fetus in fetu and discusses its clinical presentation, differential diagnosis and embryologic origin.

Occipitocervical Fetus in Fetu with Extracalvarial Extension: A Case Report

Fetus in fetu (FIF) is an extremely rare congenital anomaly in the pediatric age group. It is defined by the presence of an axial skeleton and well-formed internal organs in a fetiform mass. Only about 15 cases of intracranial FIF have been reported in the literature worldwide. We report a case of temporo-occipitocervical FIF. This 7-month-old female child presented to us with occipital swelling that she had had since birth. A soft swelling was palpable in the retroauricular region with extension into the neck. A few bony parts were palpable in the swelling. Imaging was suggestive of a multiseptate mass lesion in the right occipital region with intracranial, intraspinal and extracranial components. The patient underwent exploration and excision of the extracranial mass and retromastoid suboccipital craniectomy and decompression of the intracranial component. Different parts, such as a terminal ileum, cecum, appendix, femur, humerus and vertebral body, were identified within the mass. This case meets Willis' criteria as well as 4/5 criteria stated by Spencer for the diagnosis of this condition. To the best of our knowledge, this is the first reported case of temporo-occipitocervical FIF with a well-defined embryological spectrum. This also supports Spencer's hypothesis of abnormal twinning.

Fetus in Fetu in the Scrotal Sac: Case Report and Literature Review

Fetus in fetu (FIF) is a rare congenital anomaly. The most common site at which FIF occurs is the retroperitoneum. The mechanisms underlying the development of FIF have not been fully elucidated. The monozygotic twin theory postulates that FIF results from the unequal division of the totipotent cells of the blastocyst. However, the monozygotic twin theory does not explain all cases of FIF.Herein, we describe the clinical characteristics of a 20-day-old infant with scrotal sac swelling. Ultrasonography and computed tomography revealed the presence of a mass consistent with a FIF rather than a teratoma. Surgical removal and a subsequent pathological evaluation demonstrated that the anencephalic fetus exhibited limb buds adjacent to a palpable vertebral column, supporting the diagnosis of FIF. The infant had an uneventful recovery and was discharged on the fifth postoperative day. In the present report, the pathogenesis, presentation, diagnosis, and management of FIF, as well as new concepts emerging in this area of research, are discussed.Although the majority of cases of FIF may be diagnosed preoperatively, FIF should be distinguished from teratoma because the latter has substantial malignant potential. The recommended treatment for FIF is complete resection. To confirm the diagnosis of FIF, pathological examination, karyotyping, serologic marker assessment, and DNA restriction site mapping should be performed after removing the mass. Although FIF is thought to be a benign disorder, follow-up is necessary as a precaution against malignant recurrence, which has been described once.

Fetus in fetu: two case reports and literature review

BACKGROUND

Fetus in fetu is a rare congenital anomaly and is defined as a monozygotic twin incorporated into the abdomen of its sibling during development. Fetus in fetu is often overlooked in the differential diagnosis of an abdominal mass. Unlike teratomas, fetus in fetu is a benign disorder.

CASE PRESENTATION

We describe the clinical characteristics of two patients, a thirty-months old boy who was found to have abdominal distension and a neonate who was diagnosed antenatally with abdominal mass. Computed tomography scan revealed the mass in which the contents favor a fetus in fetu rather than a teratoma. Surgical removal revealed that the anencephalic fetus have limb buds situated relative to a palpable vertebral column, supporting the diagnosis of fetus in fetu. In the present report, presentation, diagnosis, pathology, management, and recent literature are also reviewed.

CONCLUSION

Fetus in fetu is a rare entity that typically presents in infancy and early childhood. It should be differentiated from a teratoma because of the teratoma's malignant potential. Preoperative diagnosis is based on radiologic findings. The treatment of fetus in fetu is operative to relieve obstruction, prevent further compression and possible complications. Complete excision allows confirmation of the diagnosis and lowers the risk of recurrence.

Intraventricular twin fetuses in fetu

The authors report a rare case of multiple intracranial fetuses in fetu, fulfilling Willis' traditional criteria, which include an axial and appendicular skeleton with surrounding organized tissue. This case was ascertained from studies of a full-term female neonate who presented with ventriculomegaly. A CT scan showed intracranial calcifications that were suggestive of an axial skeleton. Her birth weight was 3.176 kg (50th-75th percentile), length was 52 cm (90th percentile), head circumference was 35 cm (50th-75th percentile), and Apgar scores were 7 and 8 at 1 and 5 minutes, respectively. Prenatal ultrasonography studies performed at 12 weeks and 5 days, and 19 weeks and 6 days revealed normal findings. A 37-week prenatal ultrasonography study showed ventriculomegaly and obstructive hydrocephalus, with a possible intracranial teratoma. Cranial imaging at birth with ultrasonography, CT and MR imaging, and MR angiography demonstrated 2 complex intraventricular masses with cystic, solid, and bony elements. A craniotomy with resection of the masses was performed at 3 months of age. The infant survived and is now 12 months old with some developmental progress. Two axial skeletons, with accompanying rib cage and extremities, including well-formed feet and toes, were noted. Both anencephalic structures had skin with hair, fat, skeletal and smooth muscle, and bony structures with bone marrow and focal areas of calcification. Multiple viscera were present and included thymus, bowel, stomach, salivary gland, kidney, adrenal gland, lung, and presumed adnexal structures. A diagnosis of fetuses in fetu was rendered. Chromosomal studies of the child and tissue from the 2 fetuses in fetu showed normal female karyotypes. A single nucleotide polymorphism array analysis from the proband infant and tissue from the 2 identified fetuses in fetu appeared to be genetically identical. These results are consistent with a monozygotic twin embryonic origin of the fetus in fetu tissue, which is a mechanism that has been suggested in previous reports in which karyotypes, blood types, and limited genetic loci have been studied. This is the first report of a rare example of intracranial intraventricular twin fetuses in fetu for which a genome-wide single nucleotide polymorphism assay has confirmed their genetic identity.

Fetus in fetu from newborn's mediastinum: case report and a review of literature

Fetus in fetu is a rare congenital anomaly, when the malformed monozygotic twin is found within the body of a living child or sometimes in an adult. We report a case of fetus in fetu diagnosed during the early third trimester of pregnancy, in the medial and inferior portions of anterior mediastinum of the dominant twin. The diagnosis was suspected by prenatal ultrasound and fetal magnetic resonance imaging. It was postnatally confirmed by CT and RTG, surgically removed after birth and histologically examined. Histologically we found well-developed organs and tissues derived from all germ layers. To our knowledge, we describe the fourth case of fetus in fetu located in the thorax, and the second case located in the anterior mediastinum. This case highlights the usefulness of prenatal ultrasound and MRI in the diagnosis of mediastinal masses, and the usefulness of complete histological examination for confirmation of diagnosis of fetus in fetu. We also reviewed the possible embryologic backgrounds of this congenital anomaly.

Misdiagnosis of fetus-in-fetu as meconium peritonitis

Fetus-in-fetu (FIF) is a rare congenital condition in which a fetiform mass is detected in the host abdomen and also in other sites such as the intracranium, thorax, head, and neck. This condition has been rarely reported in the literature. Herein, we report the case of a fetus presenting with abdominal cystic mass and ascites and prenatally diagnosed as meconium pseudocyst. Explorative laparotomy revealed an irregular fetiform mass in the retroperitoneum within a fluid-filled cyst. The mass contained intestinal tract, liver, pancreas, and finger. Fetal abdominal cystic mass has been identified in a broad spectrum of diseases. However, as in our case, FIF is often overlooked during differential diagnosis. FIF should also be differentiated from other conditions associated with fetal abdominal masses.

The first histological and immunohistochemical examination of thymus in a case of fetus in fetu

Fetus in fetu (FIF) is a rare condition with less than 150 cases reported in the world to the best of our knowledge. It is a malformed monozygotic twin ("non-dominant twin"), which is found inside the body of a living child or sometimes in an adult ("dominant twin"). Different organs can be seen in these fetuses; vertebral column limbs, central nervous system, gastrointestinal tract, vessels, and genitourinary tract. In the literature, we found only two cases of fetus in fetu with the present thymic tissue. In this paper, the thymus of non-dominant twin exteriorized from the mediastini of dominant twin, was analyzed by histological and imunohistochemical methods. Even though the majority of organs did not develop normally in the mentioned case, thymic tissue was proved to be present in many body parts of the non-dominant twin. In spite of the fact that the cortex and the medulla were not so distinguishable as in the normal thymuses, presence of many basic cell populations was demonstrated: thymic epithelial cells (AE1/AE3 positive cells), T (CD45RO positive) and B (CD20 positive) cells, macrophages (CD68 positive cells), dendritic cells (S100 positive cells) and myoid cells (desmin positive). The Hassall's bodies were localized mostly in the medulla, however in sporadic cases they occurred in the area close to the connective tissue septa. The superficial epithelial cells of the Hassall's corpuscules as well as their internal contents, were markedly stained by alcian blue, and the cystic formations, found inside the Hassall's bodies, contained PAS-positive substance, similar to Hassall's bodies of normal thymuses. This fact indicates that although development of the parasitic twin is incomplete, all three germ layers participate on its development.

Fetus-in-fetu in the cranium of a 4-month-old boy: histopathology and short tandem repeat polymorphism-based genotyping. Case report

Fetus-in-fetu is a very rare condition in which one fetus is contained within another. About 100 cases have been reported, and in most of these the fetus was located in the retroperitoneum. The authors describe an extremely rare case of an intracranial fetus-in-fetu in an extraaxial location. This is the eighth intracranial fetus-in-fetu to be reported, the first intracranial extraaxial case, and involves the oldest documented patient with this condition. Histopathological analysis of the mass revealed a degenerated amnionic membranelike tissue, well-differentiated extremities (including fingerlike structures), skin, matured lungs, well-formed intestines, cerebellar and cerebral tissue, and a notochord with ganglion cells. DNA analysis using short tandem repeat polymorphisms confirmed that the fetus-in-fetu mass and the host infant had heterozygous alleles and were of identical sex and genotype.

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.