Introduction ♣ Fetus in fetu is a rare congenital anomaly ♣ Due to unequal division of totipotent inner cell mass of developing blastocyst. ♣ Result is inclusion of a small cell mass within a maturing sister embryo. ♣ Thus a vestigial remnant representing co-twin in a diamniotic monochorionic pregnancy gets incorporated within body of otherwise normally developed twin
♣ Most common site is retroperitoneum, however it has been reported in other sites as well from cranial cavity to the scrotal sac ♣ It is differentiated from teratoma by the presence of vertebral organization with limb buds and organ systems. ♣ Unlike teratomas, it is a benign condition.
Clinical presentation 2 ½ year old girl Asymptomatic Painless mass in right hypochondrium 7 x6 cm, firm, well defined, non-tender mass noted which was extending to epigastric, umbilical and right iliac fossa. Family history of paternal twinning was present.
Frontal projection Multiple dense radio-opacities in right upper quadrant of abdomen resembling well formed limb bones and spine
Computed tomography Heterogenous well defined soft tissue mass in right anterior pararenal space in suprarenal location.It showed multiple bony densities within resembling spine,limb bones,ribs,pelvic bones.These bony densities were surrounded by soft tissue and fat.
Intra-operative findings ♣ Right upper quadrant mass of 10 x12 cm covered with sac pushing liver towards left and right kidney anteriorly with stretched out right renal vessels. ♣ Vascularity is from a direct branch of IVC ♣ On opening the sac,50 ml vernix caseosa was present ♣ Anencephalic head, spine, Upper & lower limb buds with nails and partial differentiation of digits were noted.
Histopathology Gross examination Partially developed fetus with partial differentiation of 4 limbs skull & spine with palpable vertebrae,bones,scapula, ribs. Microscopy Microscopic sections showed mature derivatives of ectoderm, mesoderm and endoderm. No immature component identified. There was no evidence of somatic or germ cell malignancy. F/S/O Fetus in fetu
Specimen showing hair and limb buds Partial differentiation of vertebrae
Discussion Incidence of Fetus in fetu is 1 in 500,000 live births. Fetus in fetu occurs relatively equally in male and female patients(1) It most likely represents a monozygotic diamniotic twin that implants itself and grows within the body of its normal karyotypically identical sibling. Presents as abdominal lump(70%) The mass is located in the retroperitoneum in most cases,including our case, and is commonly surrounded by encapsulated fluid (1,2)
Fetus in fetu has been reported to occur in other locations, such as within the cranium (3),within the scrotum (4), and within the oral cavity (5) Most common presentation is a single parasitic fetus (88%), however multiple fetuses ranging from 2 to 5 have also been reported. Reported fetal size between 4- 24 cm and fetal weight varies between 1.2 kg to 1.8 kg
Controversy exists as to whether a fetus in fetu is a distinct entity or a highly organized teratoma. Willis(6) proposed that identification of vertebrae on HPE or radiology differentiates both entities. Fetus in fetu occurs in upper retroperitoneum while Teratoma occurs in the lower retroperitonium, pelvis, ovary and sacrocoocygeal region. Malignant tranformation is rare.
References 1.Hoeffel CC, Nguyen KQ, Tran TT, Fornes P. Fetus in fetu: a case report and literature review. Pediatrics 2000; 105:1335–1344. 2.Chen CP, Chern SR, Liu FF, et al. Prenatal diagnosis, pathology,and genetic study of fetus in fetu. Prenat Diagn 1997; 17:13–21. 3.Kimmel DL, Moyer EK, Peale AR, Winborne LW, Gotwalss JE. A cerebral tumor containing five human fetuses: a case of fetus in fetu. Anat Rec 1950; 106:141–165 4.Kakizoe T, Tahara M. Fetus in fetu located in the scrotal sac of a newborn infant: a case report. J Urol 1972; 107:506–508. 5.Senyuz OF, Rizalar R, Celayir S, Oz F. Fetus in fetu or giant epignathus protruding from the mouth. J Pediatr Surg 1992; 27:1493– 1495 6. Willis RA. The structure of teratomata. J Pathol Bacteriol 1935;40:1– 36.