Retroperitoneal fetus in fetu presenting in a male infant: A case report and literature review

Abstract

Fetus in fetu (FIF) is a rare congenital disease caused by the abnormal development of monochorionic diamniotic twins that appears as a cystic mass containing fetus-like structures mainly in the retroperitoneum of infants. The clinical manifestations of fetus in fetu vary, but they mostly present at infancy, hence, it should be differentiated from a teratoma. Here, we report a case of an infant with fetus in fetu in the retroperitoneum. Enhanced computed tomography scans and three-dimensional images showed a huge mixed-density mass on the left side of the abdominopelvic cavity with patchy distribution of fat, intact bones, and soft tissue. The child underwent fetus in fetu resection under general anaesthesia. Histopathology confirmed that the mass contained skin, muscle, intestinal mucosa, bones and cartilage, nerves, muscles, fat, and bone marrow tissue.

Keywords: Fetus in fetu; Infants; Rare congenital disease; Retroperitoneal.

Fig. 1

Ultrasonographic images. (A-C) Ultrasound images show a mixed-density echoic mass in the abdominal cavity with clear boundaries and slightly strong echo. (D) Color Doppler Flow Imaging(CDFI) showed blood flow signal.

Fig. 2

(A-D) Axial computed tomography images showing an intra-abdominal mass with fat, intact bones, and soft tissue displacing the bowel loops.

Fig. 3

Three-dimensional reconstruction of fetus in fetu showing long bones, skull, and dysmorphic vertebrae. (A-B) sagittal view, (C-F) coronal view.

Fig. 4

The mass was completely resected under general anaesthesia.

Fig. 5

Gross specimen of the mass. (A-B) The appearance of the mass. (C) Upon incision, the mass exhibited long bones, skull, and dysmorphic vertebrae.

Fig. 6

Pathology of the mass. (A-B) Bone, cartilage tissue, and bone marrow tissue (A: 40x, B: 100x); (C-D) Intestinal tissue (C: 40x, D: 100x); E: Muscle and fat (40x); F: Skin and appendages (40x); G: Mucosa (40x); H: Nerves (40x).