Foetus in foetu: serological assessment of monozygotic origin by automated analysis

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.

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.

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.

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.

Fetus in fetu: molecular analysis of a fetiform mass

Fetus-in-fetu is a rare condition presenting as a calcified intra-abdominal mass in the newborn infant. Over 50 cases of fetus-in-fetu have been reported since 1800. Karyotype analysis in 8 cases and protein polymorphisms in 4 documented identical findings in the host and fetiform mass. We report a case of fetus-in-fetu in a newborn female including cytogenetic and molecular studies of both the host and mass. Genotypic information from 7 polymerase chain reaction (PCR) assays representing 4 chromosomes demonstrates heterozygous and identical alleles in the infant and fetus-in-fetu at all loci studied. A review of the literature is provided including a discussion regarding the impact of molecular data on present hypotheses of fetus-in-fetu pathogenesis.

Fetus amorphus or placental teratoma?

A differential diagnosis between fetus amorphus and placental teratoma based on the presence of an umbilical cord and/or skeletal organization in the fetus amorphus has been proposed (Fox and Butler-Manual: Journal of Pathology 88:137-140, 1964). We report a description of one new case of fetus amorphus, along with the results of a critical reexamination of 96 cases from the literature. Our findings fail to support the proposed criteria for distinguishing fetus amorphus from placental teratomas. We find that the presence or absence of an umbilical cord does not relate at all to the developmental state of the specimen. The extent of skeletal development may be a more valid criterion; however, the internal organization in the fetus amorphus forms an anatomical continuum with that of the placental teratoma, making a differential diagnosis meaningless. Additional research is necessary to solve this dilemma.

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

A cystic tumor was first found in the abdomen of a Taiwanese girl at the age of 9 months. The tumor gradually increased in size and caused no symptoms until the girl was 7 years of age, when surgical removal was carried out. Pathological examination disclosed two "fetuses" within the fibrous sac. The pathogenesis of fetus in fetu and its differentiation from retroperitoneal teratoma are still controversial issues. Further work needs to be done to elucidate whether it is a natural progression of the twinning process to teratoma or the inclusion of a monozygotic diamniotic twin within the bearer.

Fetus in fetu: a fetiform teratoma

Examination of a retroperitoneal fetus in fetu, diagnosed preoperatively, revealed previously unreported histologic findings in the vascular pedicle and membranous capsule that indicated that these structures are not "umbilical cord" or "amnion." These findings include nervous innervation of both structures and a well-defined lamina elastica interna and vaso vasorum in the artery of the vascular pedicle. Thus, strong support is provided for the theory that many examples of fetus in fetu are remarkably complex, well differentiated, highly organized teratomas. Additional arguments that favor the identity of fetus in fetu and teratoma are presented.

Fetus in fetu associated with an undescended testis

Fetus in fetu is an extremely uncommon cause of an abdominal mass in the neonate; fewer than 30 generally accepted cases are recorded in the literature. We report a case of intraabdominal fetus in fetu, with a unique location within an undescended left testicle. Chromosomal studies of cells from the fetus in fetu and the surviving infant revealed identical 46,XY karyotypes.

Fetus in fetu

A 2-month-old boy was found to have an abdominal mass in the left upper quadrant. Surgical removal revealed the mass to be a fetus in fetu. Dissection and roentgenologic examination unequivocally demonstrated the presence of vertebral column and organs arranged appropriately to the vertebral axis.

Cytogenetics of extragonadal tumors

Tissue from six human extragonadal teratomas was obtained for cytogenetic study. These included two gluteal lesions in infant females, and one each of thyroid, mediastinal, sacral and gastric teratomas in males. Tissue culture characteristics indicated tumor growth. All tumors, except the mediastinal lesion showed the presumed karyotype of its host, XX or XY. The mediastinal mass was tetraploid XXYY and contained an X chromatin body and double Y bodies. Our data support the concept that extragonadal teratomas in males and females arise mitotically from diploid cells and are more similar to identical twins. No heterosexual (XX) tumors were seen in males which would be expected in parthenogenetic tumors. The sex chromatin positive tumors seen in earlier studies may have resulted from polyploidy. Thus, male and female extragonadal teratomas have a different origin from the postmeiotic ovarian teratomas.