Fetus-in-fetu (FIF) is an extremely rare abnormality that occurs secondary to abnormal embryogenesis in a monochorionic diamniotic pregnancy where a non-viable fetus becomes enclosed within a normally developing fetus.
This condition is thought to have a 2:1 male predominance 2.
Most patients present with an abdominal mass in the 1st year of life.
The exact embryogenesis of fetus-in-fetu is controversial - there are two schools of thought:
- some propose it occurs from the anomalous embryogenesis in a diamniotic monochorionic twin pregnancy in which a malformed monozygotic twin lies within the body of its fellow twin
- others consider it to represent a highly organized teratoma
Most occur in the abdomen / retroperitoneal cavity.
Other reported locations include.
- cranial cavity 4
- mediastinum 8
Plain radiograph- CT
May typically show a calcified abdominal mass with some components favoring fetal parts within the abdomen (or rarely other parts) of another neonate 2,7.
Treatment and prognosis
The treatment of choice is total excision. It is considered relatively benign.
History and etymology
Thought to be originally described by Meckel in the late 18th century 2.
This entity is distinguished from an intrabdominal teratoma by its embryological origin, its unusual location in the retroperitoneal space, its invariable benignity, and by the presence of vertebral organization with limb buds and well-developed organ systems.
- 1. Grosfeld JL, Stepita DS, Nance WE et-al. Fetus-in-fetu: An ususual cause for abdominal mass in infancy. Ann. Surg. 1974;180 (1): 80-4. - Free text at pubmed - Pubmed citation
- 2. Patankar T, Fatterpekar GM, Prasad S et-al. Fetus in fetu: CT appearance--report of two cases. Radiology. 2000;214 (3): 735-7. Radiology (full text) - Pubmed citation
- 3. Heifetz SA, Alrabeeah A, Brown BS et-al. Fetus in fetu: a fetiform teratoma. Pediatr Pathol. 1988;8 (2): 215-26. - Pubmed citation
- 4. Yang ST, Leow SW. Intracranial fetus-in-fetu: CT diagnosis. AJNR Am J Neuroradiol. 13 (5): 1326-9. AJNR Am J Neuroradiol (abstract) - Pubmed citation
- 5. Chen CP, Chern SR, Liu FF et-al. Prenatal diagnosis, pathology, and genetic study of fetus in fetu. Prenat. Diagn. 1997;17 (1): 13-21. Prenat. Diagn. (link) - Pubmed citation
- 6. Brand A, Alves MC, Saraiva C et-al. Fetus in fetu--diagnostic criteria and differential diagnosis--a case report and literature review. J. Pediatr. Surg. 2004;39 (4): 616-8. J. Pediatr. Surg. (link) - Pubmed citation
- 7. Hoeffel CC, Nguyen KQ, Phan HT et-al. Fetus in fetu: a case report and literature review. Pediatrics. 2000;105 (6): 1335-44. doi:10.1542/peds.105.6.1335 - Pubmed citation
- 8. Aoki K, Matsumoto Y, Hamazaki M et-al. MRI reveals fetus in fetu in the mediastinum. Pediatr Radiol. 2004;34 (12): 1017-9. doi:10.1007/s00247-004-1295-4 - Pubmed citation
- 9. Beaudoin S, Gouizi G, Mezzine S et-al. Mediastinal fetus in fetu. Case report and embryological discussion. Fetal. Diagn. Ther. 19 (5): 453-5. doi:10.1159/000078999 - Pubmed citation