Fetus in fetu: a case report and literature review

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.

Ultrasound diagnosis of a retroperitoneal fetus in fetu: A case report

Fetus in fetu (FIF) is a rare anomaly of diamniotic monochorionic twins, where a malformed fetus resides within the body of its twin. Most FIF occurs in the retroperitoneal region around the host spine and appears prenatally as a solid-cystic mass consisting of fetal-like structures. Imaging has an important role in the diagnosis of FIF. The present study reported a single case, a 45-year-old woman, with a teratoma in a third-trimester fetus diagnosed after prenatal ultrasonography (US), which showed a mass containing fetus-like echoes. FIF was considered after the US showed that the mixed solid-cystic retroperitoneal mass around the vertebral axis of the host fetus consisted of two separate masses, each containing distinct fetal visceral structures. One fetus was acardiac and the other parasitic fetus was visible with a weak heartbeat. Postpartum magnetic resonance imaging and ultrasonography (US) scans of the newborn showed a retroperitoneal cystic space-occupying mass with distinctive limbs and visceral structures. The pathological examination further confirmed the diagnosis of retroperitoneal FIF. Also, a prenatal US could detect FIF in utero. A cystic-solid mass containing long bones, vascular pedicles, or visceral structures around the vertebral axis of the host fetus in the US might suggest the possibility of a FIF.

Fetus-in-fetu: mimicking teratoma on antenatal ultrasound

Objectives

Fetus-in-fetu is a rare congenital anomaly that occur secondary to abnormal embryogenesis in a diamniotic monochorionic pregnancy. Its diagnosis can be accurately made by imaging ultrasonography, radiography, computed tomography, or magnetic resonance imaging. Differential diagnosis is an important issue because FIF, teratoma and cystic meconium peritonitis are very different in terms of their respective disease courses.

Case presentation

This is an interesting rare case of a 22-year-old pregnancy woman, presented for a routine antenatal ultrasound. The diagnosis of a fetus-in-fetu was suspected, complete surgical excision of the lesion was performed and the diagnosis was histopathologically confirmed

Conclusions

We describe also the common characteristic of FIF as revealed by prenatal and postnatal US, postnatal MRI, and the operative findings.

The First Case of Fetus in Fetu in Nicaragua: The Management Experience of the Pediatric Neurosurgery Team

Fetus in fetu (FIF) is a rare congenital anomaly of asymmetric monozygotic twins, where the parasitic twin develops abnormally inside the body of the host twin. In most cases, it is incorporated into the sibling's abdomen, which frequently presents as a retroperitoneal mass. Currently, at least 200 cases have been reported worldwide, being this the first case in Nicaragua. We describe a case of a male newborn, born via cesarean section, with a history of multiple congenital malformations observed via ultrasound examination. At birth, a mass is observed on its dorsum that impresses a skull, but without the presence of bones, with three limbs, two upper and one lower, with an outline located transversely on the pelvic girdle and the presence of two male genitalia with agenesis of the testicles and an accessory kidney. A preoperative diagnosis of FIF and spinal dysraphism was made by computed tomography (CT) and magnetic resonance imaging (MRI). They shared a spinal cord and had the presence of an open spinal defect type meningocele with aberrant roots. After the diagnosis and discussion, the multidisciplinary team proceeded to surgery to perform the separation of the twin (FIF). The subsequent anatomopathological examination revealed that the fetus was anencephalic and had reliable FIF characteristics. The resection was performed followed by the closure of the 430 mL meningocele and complete separation of the spine and the parasitic twin. We present the first case of fetus in fetu in Nicaragua.

Fetus in fetu: use of intraoperative ultrasound for safe excision of a rare entity

A prenatally diagnosed abdominal mass at 36 weeks and 0 days was further characterised by postnatal ultrasound and MRI to be likely a rare case of fetus in fetu in an otherwise healthy male. Due to close proximity to both the coeliac axis and superior mesenteric artery (SMA), surgical excision was delayed for several months. Interim CT with intravenous contrast performed at 2 months of age demonstrated the SMA travelling through the posterior aspect of the mass. Surgery proceeded at 2 months of age. Intraoperative ultrasound was used to definitively identify both the coeliac axis and SMA in order to facilitate a safe excision. The patient recovered well with an uneventful discharge to home on postoperative day 8. Pathology confirmed the diagnosis of fetus in fetu.

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.

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.

Intra-abdominal fetus in fetu presenting at 31 weeks gestational age

Fetus in fetu (FIF) is a rare anomaly of diamniotic monochorionic twins, in which a malformed fetus resides in its twin's body. This report shows a case with the prenatal diagnosis of FIF at Tu Du hospital. A 23-year-old woman, first-time pregnant, presented at the hospital with an abdominal mass in the fetus at 31 weeks and 4 days of gestation. The ultrasound showed an abnormal mass with the images of calcified features located in the left hypochondriac region and the kidney's upper pole. These images had shapes of skull, femur, spine and became more apparent as the fetus grew. Then, the patient was monitored and delivered at our hospital. The infant was moved to the Children's Hospital 1 and diagnosed with FIF by ultrasound. The surgical resection was performed at 12 days of birth.

A case report of fetus in fetu with an aorta-like structure visualized by contrast-enhanced CT

Fetus in fetu (FIF) is a rare congenital anomaly resulting from abnormal embyogenesis in monochorionic diamniotic twins and appears as a cystic mass containing fetus-like structures mainly in the retroperitoneum of infants. Although there is a theory that FIF is a highly differentiated teratoma, it is commonly distinguished from teratoma as a mass containing a vertebral axis with appropriate arrangement of limbs or other organs around this axis. Here we present a case of FIF with aorta-like structure visualized by contrast-enhanced computed tomography. A 5-day-old girl was pointed out a cystic mass in the abdomen by ultrasound examination. Abdominal contrast-enhanced computed tomography revealed a retroperitoneal cystic mass with spine- and limb-like bone structures and blood vessel-like elongated structures and it was confirmed as FIF by surgery. The presence of major vascular structures along the skeletal axis is clearly different from teratoma and suggests that it occurred as an embryo and underwent some stage of development. Our findings strongly support the monozygotic twin theory.

Lumbar fetiform teratoma; a case report

Fetiform teratoma is a rare highly developed mature teratoma with organoid differentiation although it is not as developed as fetus in fetus which is the only differential diagnosis of this entity. It should be distinguished from the fetus in fetu by absence of the axial skeleton. A 6-month-old baby girl with a lumbar lump underwent ultrasonography, CT-scan and surgery. On imaging, a sac-like structure was noted in the lumbar region containing bowel segments, mesentery-like structure and few lymph nodes. The patient underwent surgery. The entire sac with its content were completely excised. Very few cases of fetiform teratoma have been reported in English literature however to the best of our knowledge lumbar fetiform teratoma has not been reported up to now. Highly developed teratoma is a diagnostic dilemma as it resembles fetus in fetu. The absence of a spinal axis differentiates this entity from the fetus in fetu.

Human germ cell tumours from a developmental perspective

Human germ cell tumours (GCTs) are derived from stem cells of the early embryo and the germ line. They occur in the gonads (ovaries and testes) and also in extragonadal sites, where migrating primordial germ cells are located during embryogenesis. This group of heterogeneous neoplasms is unique in that their developmental potential is in effect determined by the latent potency state of their cells of origin, which are reprogrammed to omnipotent, totipotent or pluripotent stem cells. Seven GCT types, defined according to their developmental potential, have been identified, each with distinct epidemiological and (epi)genomic features. Heritable predisposition factors affecting the cells of origin and their niches likely explain bilateral, multiple and familial occurrences of the different types of GCTs. Unlike most other tumour types, GCTs are rarely caused by somatic driver mutations, but arise through failure to control the latent developmental potential of their cells of origin, resulting in their reprogramming. Consistent with their non-mutational origin, even the malignant tumours of the group are characterized by wild-type TP53 and high sensitivity for DNA damage. However, tumour progression and the rare occurrence of treatment resistance are driven by embryonic epigenetic state, specific (sub)chromosomal imbalances and somatic mutations. Thus, recent progress in understanding GCT biology supports a comprehensive developmental pathogenetic model for the origin of all GCTs, and provides new biomarkers, as well as potential targets for treatment of resistant disease.

Fetus in fetu in an adult woman

Fetus in fetu (FIF) is an extremely rare condition in which malformed fetus is found most commonly in the retroperitoneum of living twin. It occurs in about 1 in 500 000 live births and less than 200 cases have been reported in medical literature. We report FIF in a 17-year-old woman unlike other cases which were usually detected in early age and in male gender. This is the eighth case of adult FIF and the first case of FIF in adult woman worldwide. Preoperative diagnosis of FIF on CT was made and planned for exploratory laparotomy. The excised malformed fetus in a sac was proven as FIF on the basis of histopathological examination. In view to avoid such late presentation, early detection of FIF with radiological imaging in clinically suspected case is recommended. Surgical excision is the ideal treatment even teratoma is the differential diagnosis.

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.

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

Fetus in fetu is an extremely rare congenital anomaly. We describe the perinatal diagnosis and management of a fetus with oropharyngeal and cervical fetus in fetu. High-resolution ultrasonography with 3-dimensional rendering can identify increased risks of airway obstruction in utero. Early identification allows a multidisciplinary team to be assembled for a scheduled ex utero intrapartum treatment procedure.

Impact of prenatal diagnosis of fetus-in-fetu

Fetus in fetu (FIF) is an extremely rare condition (1/500,000 live births) in which a fetiform structure is incorporated into the body of its twin. FIF can be a diagnostic dilemma due to its similarity to a teratoma, but identification of FIF is important for subsequent medical and surgical management. We compare two cases of fetal masses diagnosed on prenatal imaging that were later identified as FIF through further radiological, surgical, and pathologic evaluation. We use these cases to illustrate key pre- and postnatal features of FIF and highlight the benefits of prenatal detection and follow-up for postnatal management.

Fetus in Fetu—A Case Report with a Variant Host Anastomosis

Fetus in fetu is a rare congenital condition where a vertebrate fetus is found within the body of its host twin. It features a monozygotic parasitic twin attached via a vascular anastomosis to its host circulation. This report describes an instance of fetus in fetu with a variant presentation of its vascular pedicle to its host via the inferior epigastric vasculature.

Management of fetal teratomas

Fetal teratomas are the most common tumors diagnosed prenatally. The majority of these tumors are benign and cured by complete resection of the mass during the neonatal period. Prenatal diagnosis has improved the perinatal management of these lesions and especially for the teratomas that might benefit from fetal intervention. A comprehensive prenatal evaluation including conventional ultrasounds, Doppler, echocardiography and fetal MRI, is essential for an effective counseling and perinatal management. Antenatal counseling helps the parents to better understand the natural history, fetal intervention, and perinatal management of these tumors, which differ dramatically depending on their size and location. Fetal surgical debulking improves survival in cases of sacrococcygeal teratoma with cardiac decompensation. Additionally, the use of an EXIT procedure reduces the morbidity and mortality if a complicated delivery in cases of cervical and mediastinal teratomas. Here, we offer an overview of all fetal teratomas and their recommended management, with emphasis on in utero treatment options.

Parasitic twin--a supernumerary limb associated with spinal malformations. A case report

We describe a case of rachipagus parasitic twin with spinal cord malformations (lipomyelomeningocele and tethered cord) in a 7-month-old Ethiopian infant. The parasitic mass had a well-formed foot, ankle and lower leg and a small sinus that resembled an anus. Magnetic resonance imaging scans revealed spinal malformations including a distal syringohydromyelia. The mass was successfully resected and the dural attachment was closed. Histopathological examination confirmed the diagnosis. Postoperatively, the child had unchanged, intact neurological function in both lower limbs. Almost all rachipagus parasitic twins are associated with spinal malformations. They should, therefore, be operated on by surgeons experienced in myelomeningocele surgery.

A review of the mechanisms and evidence for typical and atypical twinning

The mechanisms responsible for twinning and disorders of twin gestations have been the subject of considerable interest by physicians and scientists, and cases of atypical twinning have called for a reexamination of the fundamental theories invoked to explain twin gestations. This article presents a review of the literature focusing on twinning and atypical twinning with an emphasis on the phenomena of chimeric twins, phenotypically discordant monozygotic twins, mirror-image twins, polar body twins, complete hydatidiform mole with a coexistent twin, vanishing twins, fetus papyraceus, fetus in fetu, superfetation, and superfecundation. The traditional models attributing monozygotic twinning to a fission event, and more recent models describing monozygotic twinning as a fusion event, are critically reviewed. Ethical restrictions on scientific experimentation with human embryos and the rarity of cases of atypical twinning have limited opportunities to elucidate the exact mechanisms by which these phenomena occur. Refinements in the modeling of early embryonic development in twin pregnancies may have significant clinical implications. The article includes a series of figures to illustrate the phenomena described.

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.

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

Fetus in fetu (FIF) is a rare form of twinning in which an immature twin develops parasitically inside the other twin. The most frequent location of a parasitic fetus is the retroperitoneal region. 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.

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.

Lumbosacral lipomyelomeningocele with anomalous osseous limb in a 3-month-old female

A patient with lipomyelomeningocele (known in utero) presented for MRI characterization prior to surgical procedure at three months of age. Cross-sectional imaging revealed a spinal dysraphism of the lower lumbar spine, with a posterior spinal defect spanning L4 to S2 subcutaneous fat intrusion, and distal spinal cord extrusion. An osseous excrescence was also appreciated, articulating with the left iliac bone. This case demonstrates the youngest known lipomyelomeningocele with accessory limb and the abnormal growth of multiple tissue types at the site of spinal dysraphism-a potential consequence of dedifferentiated cell proliferation originating from a secondary neural tube defect or rachipagus parasitic twinning.

Fetus in fetu: an institutional experience

The objective of this article is to present an analysis of cases of fetus in fetu (FIF) diagnosed at our institute and to compare our data to that of the published literature. This is a retrospective analysis of cases of FIF diagnosed at our institute from January 2000 to December 2012. Details of clinical and investigational data pertaining to cases of FIF were retrieved from hospital records, and were analyzed and summarized. Literature was reviewed and our data were compared to that of published cases. We evaluated seven cases (4 males and 3 females) of FIF during the study period. The age of patients ranged from two days to 15 years. The most common site of occurrence in our study was the retroperitoneum, with the most common presenting feature being an abdominal mass. Radiology showed a solid-cystic mass. Pathologic findings were diagnostic of FIF. Most findings of our study matched with those reported in literature. The condition of FIF must be included in the differential diagnosis of abdominal masses, especially in children. This entity must be differentiated from the more commonly occurring teratoma, which can be done based on its unique clinical, radiologic, and pathologic characteristics. To our knowledge, this is the longest series of cases of FIF reported from a single institute.

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.

Increased incidence of retroperitoneal teratomas and decreased incidence of sacrococcygeal teratomas in infants with Down syndrome

Individuals with Down syndrome (DS) have a unique profile of neoplasms, with a higher incidence of leukemias and a lower incidence of solid tumors than seen in the general population. We recently encountered two cases of infants with DS with retroperitoneal teratoma. After reviewing the literature on teratomas in DS, we found that the incidence of retroperitoneal teratomas was higher and the incidence of sacrococcygeal teratomas was lower in infants with DS than in the general population.

Sacrococcygeal fetiform teratoma altman type 1: a rare case report in a 11 year old girl

Fetiform teratoma (homunculus) is a rare but distinct entity, characterized by presence of more organoid differentiation than the classical teratoma but not enough to classify as fetus-in-fetu. Presence of rudimentary limbs in presence/absence of axial skeleton is often reported as an important differentiating feature. Sacrococcygeal location has been reported in a few case reports but in neonates only. This is a rare case of sacrococcygeal fetiform teratoma (Altman type 1) in an 11-year-old girl presenting as a gluteal mass.

Fetus in fetu in a neonate: report of a case

Fetus in fetu (FIF) is a rare condition in which a malformed fetus resides in the body of its host. The presence of a well-formed vertebral column secures the diagnosis of FIF and differentiates this entity from a teratoma. Although more than 100 cases of FIF have been reported in the literature, the presence of a well-formed vertebral column is not documented in many cases. We herein report the case of a 19-day-old female who presented with a lump in the abdomen. Plain radiograph of the abdomen showed the presence of a well-formed vertebral column with long bones, and the results were confirmed with ultrasonogram and CT scans. Therefore, a preoperative diagnosis of FIF was made, and the mass was successfully excised. Upon opening the sac of the mass, a malformed anencephalic fetus was found.

Revisiting fetus-in-fetu

Fetus-in-fetu is a rare congenital anomaly in which a malformed parasitic twin is found within the body of its partner. Less than 100 cases have been reported in published studies. Although it is a relatively benign condition, clinicians need to have a high index of suspicion for the associated complications that may arise. We report the case of an infant presenting with jaundice and steadily growing abdominal mass, who was diagnosed with fetus-in-fetu syndrome. We review the published studies and discuss the pathophysiology, complexities, and management options.

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: A Rare Congenital Anomaly

Two cases of fetus-in-fetu, on which we performed surgery in 2003 and 2006, are being reported. Both the cases presented with a lump in the abdomen. Radiology confirmed the diagnosis. The lumps were found in the retroperitoneum and successfully excised. Because of the rarity of the condition, these two cases are being reported with relevant salient features and are discussed in the light of available literature.

Diagnostic dilemma in a neglected case of fetus-in-fetu solved with Magnetic Resonance Imaging and MDCT--a case report and review of literature

Fetus-in-fetu (FIF) is a rare anomaly in which a vertebrate fetus is enclosed within the body of its twin in diamniotic monochorionic pregnancy. To the best of our knowledge, fewer than 100 cases have been reported in literature. Although a wide variety of presentations have been described in clinical reports, the characteristic features on MRI which distinguish FIF from teratoma have not been well delineated. Here we present a case of fetus-in-fetu in which characteristic MDCT and MR findings were used to diagnose FIF preoperatively and successfully differentiate it from teratoma. Although both CT and MRI can be used for definitive preoperative diagnosis of FIF, MRI is an ideal imaging modality due to inherent high tissue contrast and spatial resolution. Furthermore, MRI obviates the need for iodine contrast and eliminates the risk of ionizing radiation. We emphasize that MRI is an ideal valuable diagnostic tool for definite preoperative diagnosis of FIF and surgical planning.