Fetus-in-fetu in the pelvis: report of a case and literature review.
BACKGROUND
Fetus-in-fetu is an extremely rare condition in which a malformed fetus is found in the body of its twin. To our knowledge, fewer than 100 cases have been reported. Wide variations of presentation have been described, although its embryo-pathogenesis and differentiation from a teratoma have not been well established.


METHODS
We describe a male neonate with a fetoid-like mass in his pelvis associated with bilateral undescended testes. The mass was detected on prenatal ultrasound scans. The diagnosis of fetus-in-fetu was considered prenatally and confirmed on a computed tomography scan after birth.


RESULTS
The mass was successfully excised. Histological examination, accompanied by a review of the literature, confirmed that the mass had features consistent with a fetus-in-fetu.


CONCLUSIONS
Although an extremely rare clinical entity, fetus-in-fetu can be diagnosed prior to surgery with current imaging modalities. When it arises in the retroperitoneum of a male infant, it can hinder the descent of the testes. Complete excision is curative.
Chua
J H Y
JH
Department of Padediatric Surgery, KK Women's and Children's Hospital, Singapore. joyce.chua.h.y@singhealth.com.sg
Chui
C H
CH
Sai Prasad
T R
TR
Jabcobsen
A S
AS
Meenakshi
A
A
Hwang
W S
WS
D003456:Cryptorchidism / Q000175:diagnosis; D003937:Diagnosis, Differential; D005260:Female; D005315:Fetal Diseases / Q000175:diagnosis / Q000601:surgery; D005333:Fetus / Q000002:abnormalities* / Q000601:surgery; D006801:Humans; D007231:Infant, Newborn; D010535:Laparoscopy; D008297:Male; D011247:Pregnancy; D011859:Radiography; D012187:Retroperitoneal Space / Q000000981:diagnostic imaging; D013724:Teratoma / Q000175:diagnosis; D016216:Ultrasonography, Prenatal