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Background: The fetu in fetu (FIF) is an extremely rare congenital condition characterized by a 2nd fetus that grows into the body of the healthy twin. Its thoracic location is more exceptional. Case presentation: We report a case of intrathoracic mass in a 5-month-old female infant, diagnosed after an assessment for respiratory distress. She underwent an emergency left thoracotomy which allowed for the removal of a large thoraco-mediastinal mass inside a membranous sac containing a clear liquid mixed with vernix caseosa. The mass was completely covered with normal skin, three lobes similar to rudimentary outline of the head and limb. It was attached to a single large vascular pedicle. The pathological examination concluded that there was a high possibility of FIF. The postoperative follow-up was uncomplicated, and the child is still in good clinical condition after the 5-month follow-up. Conclusion: The assessment of the respiratory distress in an infant with a mass centered by an axial skeleton on the chest x-ray and thoracic CT scan may suggest a diagnosis of intrathoracic FIF. [ABSTRACT FROM AUTHOR]

Fetus in fetu (FIF) is an exceedingly rare congenital anomaly characterized by the presence of a partially developed fetus within the body of its twin. It is a rare entity with fewer than 200 cases documented worldwide. Typically presenting as an abdominal mass in early childhood, this condition remains a diagnostic challenge due to its infrequency and varied clinical manifestations. We present the case of a 1-year-old female child referred to the pediatric surgery department due to an abdominal mass detected by her parents. Physical examination revealed a firm, ill-defined mass in the right upper abdomen. Ultrasonography delineated a heterogeneous, calcified mass in the right upper quadrant. Laboratory investigations (complete blood count, viral markers), including tumor markers (AFP, beta-hCG), were within normal limits. A midline laparotomy was performed, and intraoperative findings revealed a well-encapsulated mass adherent to the retroperitoneum, adjacent to the liver. Careful dissection was carried out to preserve vital structures, and the mass was successfully removed without rupture. Histopathological examination confirmed the diagnosis of fetus in fetu, displaying a spectrum of tissues reminiscent of embryonic development, including skin, adnexal structures, brain tissue, mature cartilage, adipose tissue, bone marrow elements, and a partially developed vertebral column. After the surgical resection, the patient experienced an uneventful postoperative recovery. At one year of follow up the patient has shown no signs of recurrence. FIF is characterized by diagnostic challenges, often requiring postoperative histological confirmation. Histopathological examination confirmed the presence of FIF. Surgical excision, is crucial for favorable outcomes, especially in preventing potential complications. Comprehensive histopathological evaluation remains imperative for accurate diagnosis. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Fetus in Fetu (FIF) is a rare congenital anomaly in which a malformed parasitic twin is found within the body of a living child or adult. In this case report, an 18 month-old male child presented with a large abdominal mass and failure to thrive. Imaging studies confirmed the presence of a large retroperitoneal fetus in fetu with significant mass effect of the adjacent structures. A surgical resection was performed and pathology confirmed the diagnosis. These rare cases have become more frequently reported and a review of the literature for the past 15 years will describe the demographics, updated genetic findings, pathology and outcomes of this unusual tumor. Recent findings will also discuss an infrequent association with teratomas that may warrant a longer follow-up for surveillance of malignancy. [ABSTRACT FROM AUTHOR]

Fetus in fetu is a rare, nonviable, malformed parasitic twin, which grows within the body of its partner. It has been known as being almost always anencephalic and rarely reported to have an immature teratoma component. We report a case of a sacrococcygeal fetus-in-fetu with brain tissue seen on both imaging studies and pathologic specimens, containing an immature teratoma component on pathologic examinations. Imaging studies including plain radiography were very helpful for the correct diagnosis. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

Fetus in fetu is a rare clinical entity consisting of malformed fetus inside body of the living partner. It is a mass containing a vertebral axis and often other organs and/or limbs. Unlike other classical cases, this case was not having a vertebral axis but other clinico-pathological findings were suggestive of fetus in fetu. To include such types of cases, the traditional definition by Willis of fetus in fetu needs revision. [ABSTRACT FROM AUTHOR]

Fetus in fetu (FIF) in the scrotal sac is often overlooked in the differential diagnosis of other scrotal swellings in infants and children. Unlike teratoma, FIF is a benign disorder. Scrotal FIF is extraordinarily rare and has been reported only twice in the international literature. We describe the case of a 15-day-old neonate who presented with scrotal swelling since birth. Radiography and ultrasound revealed a FIF. On surgical removal and pathological evaluation, the anencephalic fetus had limb buds, male external genitals, and vertebral column, supporting the diagnosis of FIF. FIF in the scrotum is a very rare entity. It should be differentiated from other scrotal swellings such as teratoma because of the malignant potential of the latter. Preoperative diagnosis is based on radiologic findings. The treatment is complete excision. [ABSTRACT FROM AUTHOR]

Fetus in fetu is a rare congenital entity in which a deformed parasitic twin develops within the body of a living newborn or a child. Meanwhile, fetiform teratoma is a rare congenital disorder with high degree of organoid differentiation resembling fetus in fetu. We present two cases of the rare entities with two unusual locations. A 1-week-old baby boy with a large anterior abdominal mass underwent CT-scan. A large mass containing pelvic bones, femora, tibia, fibula, fused kidneys, urinary bladder, hepatic parenchyma, brain tissue and spinal cord was noted in the anterior abdominal wall. The liver parenchyma of the host twin was fused with the hepatic parenchyma of the parasitic twin. Another 6-month-old baby girl with a large 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. Both cases are rare congenital anomalies and are a diagnostic challenge. It has been described that the presence of axial skeleton and limb buds differentiates the fetus in fetu from the fetiform teratoma, therefor, the first case was diagnosed as fetus in fetu and the latter one as fetiform teratoma. [ABSTRACT FROM AUTHOR]

Abstract Fetus-in-fetu (FIF) is a rare condition in which malformed parasitic twin grows inside the body of its twin and usually presents as abdominal mass. We are reporting a case of neonate who presented with abdominal mass; FIF was suggestive after further radiological studies. Intra-operatively, retroperitoneal mass was identified in the sub hepatic region and successfully resected. Post operatively patient recovered well and discharged in good condition. [ABSTRACT FROM AUTHOR]

Abstract: Fetus in fetu (FIF) is a rare cause of abdominal mass in children. One of the malformed monozygotic diamniotic twins is located in the body of other twin. It is differentiated from teratoma by the presence of vertebral organization with limb buds and other organ systems. Diagnosis is based on radiologic findings. Surgical excision is the treatment of choice, leading to the complete removal of the mass. To our knowledge, less than 200 cases have been described in the literature. Herein, we report 2 cases of FIF, a newborn who was diagnosed antenatally and a three-and-half-year- old boy diagnosed with mediastinal FIF after admission for recurrent respiratory tract infections. [Copyright &y& Elsevier]