title: Antenatal diagnosis of a third ventricular mass: fetus in fetu or teratoma?
abstract: BACKGROUND
  Fetus in fetu (FIF) is a rare condition in medicine where an aberrant monozygotic twining results in inclusion of a degenerated fetus inside its twin bearer. Whereas FIF is generally defined as a fetiform vertebrate mass, teratoma is considered as a tumor composed of disorganized tissues derived from the three embryological layers. Recent data plead for a common origin and suggest a continuum between FIF and teratoma.
  
  
  METHODS
  We describe the case of an intraventricular mass diagnosed by prenatal imaging and associated with triventricular hydrocephalus. Surgical removal of a non-vertebrate mass covered by normal skin was performed when the child was 15 months old. Now aged of 30 months, the child continues to develop normally. Histological data were in favor of a FIF.
  
  
  CONCLUSIONS
  We discuss the diagnosis, pathogenesis, and prognosis in the light of data from the recent literature.
  
  
  CONCLUSIONS
  Aberrant monozygotic twining leading to inclusion of a degenerate fetus inside its twin bearer results in FIF or teratomas. Surgical removal represents the main treatment. Intracranial FIF remains an extremely rare congenital condition, with a favorable oncological prognosis; the developmental prognosis appears conditioned by the absence of other malformation, the small size of the lesion, and the early management of intracranial hypertension.
authors.affiliation: Department of Pediatric Neurosurgery, Hôpital Roger Salengro, Centre Hospitalier Régional et Universitaire de Lille, Lille, France. dominique.marnet@laposte.net
authors.forename: Dominique
authors.initials: D
authors.lastname: Marnet
authors.forename: Matthieu
authors.initials: M
authors.lastname: Vinchon
authors.forename: Olivier
authors.initials: O
authors.lastname: Kerdraon
authors.forename: Sylvie
authors.initials: S
authors.lastname: Joriot
authors.forename: Caroline
authors.initials: C
authors.lastname: Chafiotte
authors.forename: Patrick
authors.initials: P
authors.lastname: Dhellemmes
mesh_terms: D002551:Cerebral Ventricle Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology* / Q000601:surgery; D003937:Diagnosis, Differential; D005333:Fetus / Q000002:abnormalities* / Q000473:pathology; D006801:Humans; D006849:Hydrocephalus / Q000209:etiology* / Q000601:surgery; D007223:Infant; D007231:Infant, Newborn; D011296:Prenatal Diagnosis; D013724:Teratoma / Q000000981:diagnostic imaging / Q000473:pathology* / Q000601:surgery; D020542:Third Ventricle / Q000002:abnormalities* / Q000601:surgery; D016896:Treatment Outcome; D016216:Ultrasonography, Prenatal