title: Fetus-in-fetu: parasite or neoplasm? A study of two cases.
abstract: BACKGROUND
  Fetus-in-fetu is a rare congenital fetiform mass whose etiology is still controversial. We report two cases of fetus-in-fetu. CASE 1: A fetal retroperitoneal cystic tumor including two masses was detected by ultrasonography at 26 gestational weeks. The masses showed distinctive structures resembling a vertebral axis and were prenatally diagnosed as fetus-in-fetu. A resected specimen revealed two fetiform masses. CASE 2: An intracranial tumor with hydrocephalus was detected by ultrasonography at 19 gestational weeks. The pregnancy was terminated, and a postmortem examination revealed six fetiform masses with immature teratoma.
  
  
  CONCLUSIONS
  The tumors may possibly consist of parasitic monozygotic diamniotic twins or highly differentiated teratomas.
authors.affiliation: Department of Obstetrics, Kanagawa Children's Medical Center, Yokohama, Japan.
authors.forename: Keisuke
authors.initials: K
authors.lastname: Saito
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Katsumata
authors.forename: Tomoo
authors.initials: T
authors.lastname: Hirabuki
authors.forename: Keisuke
authors.initials: K
authors.lastname: Kato
authors.forename: Michiko
authors.initials: M
authors.lastname: Yamanaka
mesh_terms: D000328:Adult; D000818:Animals; D005260:Female; D005315:Fetal Diseases / Q000000981:diagnostic imaging* / Q000469:parasitology*; D005333:Fetus; D006801:Humans; D009369:Neoplasms / Q000000981:diagnostic imaging*; D010271:Parasites; D011247:Pregnancy; D013724:Teratoma / Q000000981:diagnostic imaging; D014427:Twins; D014463:Ultrasonography