FETUS in fetu is a rare condition commonly presenting as an epitomized pedunculated vertebrated fetiform mass in a newborn infant. Different kinds of presentation and locations have been reported in the hosts. Although numbers of instances have been reported the fascination and curiosity about other presentations and genesis of FETUS in fetu remains confirmed. In Tabriz pediatric surgery ward we have had five different presentations of FETUS in fetu. The aim of this case series and a subtle literature review is gathering these interesting presentations.

The FETUS in fetu (FIF) is statement which is used to describe one of the asymmetrical monozygotic twinning. In this kind of twinning, which is also called endoparasitic, one of the FETUSes grows like a parasite inside the other one. Endoparasitic twins are usually located in the upper abdominal retroperitoneum with close anastomosis to the vitellin circulation and it consists of vertebrae, dermal structures, extremities, intestine and neural tissues. Less commonly they have gonads, adrenals, heart and lungs. The sex ratio is equal. Presented here is a case report from Iran.

Background FETUS-In-Fetu (FIF) is a rare congenital malformation, which consists of a FETUS mixed with a distinct tissue that is from the other FETUS of the twin. FIF is defined as a mass containing a vertebral axis that is often associated with other organs or limbs around this central axis. Case Report The patient was a two days old girl infant who was referred to the Taleghani Pediatric Center of Gorgan, Iran, due to a mass in sacral area measuring 8. 5 x 12. 5 cm with soft consistency containing a normal skin colored fluid with blood streaks and hemorrhagic and bruise colored patches since birth. The results of the mother's ultrasound in the fourth month of pregnancy had identified the cyst for the FETUS. In the primary results of imaging, the first diagnosis was type 2 Sacrococcygeal teratoma (SCT). However, results of post-birth graph confirmed the presence of fetal bone structure in the infant's sacrum, so FIF was diagnosed for the infant. Conclusion Current imaging modalities enable accurate diagnosis before surgery. Complete resection is generally curative and allows confirmation of the diagnosis.

Reproduction in domestic animals, as a major source of food and other products for human, as great importance and study of related subjects including sex differentiation and gonadogenesis during fetal life can solve many questions on normal development and various disorders of urogenital system. Since studies on sex differentiation in goat FETUS are scarce, this study was performed. Twenty-five goat FETUSes with 5–40 mm crown-rump lengths (CRL) were obtained from slaughter-house and fixed in 10% formalin solution immediately. The development and features of external genitalia of these FETUSes as well as their sex differentiation were then examined. In externally indifferentiated FETUSes, the cranial half of the body was cut away at the diaphragmatic level and serial sections, 6-micron thickwere prepared and the ovarian and testicular differentiation was studied. Results showed that considering the development of the external genitalia, external sex differentiation occurs at 31 mm CRL in male FETUSes and at 33 mm CRL in female FETUSes. Microscopic studies suggested that testicular tissue differentiation occurs at 23 mm CRL with formation of tunica albuginea and medullary cords. Ovarian tissue differentiation occurs at 38 mm CRL with establishment of cortical and medullary regions.