title: Fetus in Fetu: Case Report and Brief Review of Literature on Embryologic Origin, Clinical Presentation, Imaging and Differential Diagnosis.
abstract: 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.
  
  
  METHODS
  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.
authors.affiliation: Department of Radio-Diagnosis, Jawaharlal Institute of Postgraduate Medical Education and Research, Puducherry, India.
authors.forename: Suhas Aithal
authors.initials: SA
authors.lastname: Sitharama
authors.affiliation: Department of Pediatric Surgery, Jawaharlal Institute of Postgraduate Medical Education and Research, Puducherry, India.
authors.forename: Bibekanand
authors.initials: B
authors.lastname: Jindal
authors.affiliation: Department of Pediatric Surgery, Jawaharlal Institute of Postgraduate Medical Education and Research, Puducherry, India.
authors.forename: Mrudula Kumari
authors.initials: MK
authors.lastname: Vuriti
authors.affiliation: Department of Pediatric Surgery, Jawaharlal Institute of Postgraduate Medical Education and Research, Puducherry, India.
authors.forename: Bikash Kumar
authors.initials: BK
authors.lastname: Naredi
authors.affiliation: Department of Pediatrics, Jawaharlal Institute of Postgraduate Medical Education and Research, Puducherry, India.
authors.forename: Sriram
authors.initials: S
authors.lastname: Krishnamurthy
authors.affiliation: Department of Radio-Diagnosis, Jawaharlal Institute of Postgraduate Medical Education and Research, Puducherry, India.
authors.forename: Deepak Barathi
authors.initials: DB
authors.lastname: Subramania
keywords: Diagnostic Imaging; Retroperitoneal Neoplasms; Teratoma; Twinning, Monozygotic