Fetus in Fetu: Case Report and Brief Review of Literature on Embryologic Origin, Clinical Presentation, Imaging and Differential Diagnosis

Abstract

SummaryBackgroundFetus in fetu (FIF) is a rare entity in which a malformed diamniotic monochorionic parasitic fetal twin develops inside a normal co-twin’s body, most commonly in the abdominal cavity. FIF is differentiated from the teratoma by the presence of vertebral column often with an appropriate arrangement of other organs or limbs around it.Case ReportA two-and-a-half-year-old girl presented with a painless abdominal swelling in the right hypochondrium. On imaging, a heterogenous soft tissue mass with internal calcific densities was noted in the retroperitoneum. The mass had vertebral organization, limb and pelvic bones. The presence of a fetiform teratoma was suspected and surgery revealed an encapsulated mass with an anencephalic head, spine, upper and lower limb buds. Histopathology confirmed the presence of a fetus in fetu. The postoperative period was uneventful with no evidence of recurrence.ConclusionsFIF is a pediatric rarity. Cross-sectional imaging helps in differentiating it from a teratoma, meconium peritonitis and abdominal ectopic pregnancy. Surgical excision is the treatment of choice for this benign condition, which requires a follow-up only in certain cases. This case report describes a retroperitoneal fetus in fetu and discusses its clinical presentation, differential diagnosis and embryologic origin.

Case report: rare congenital anomaly diagnosed by ultrasonography

“…The most common localization of FIF is in the retroperitoneal space, but has already been reported in the abdomen, scrotum, kidneys, adrenal, mediastinum, thorax, skull and lymph. 10,11 It is usually not a malignant condition, but it can cause abdominal distension, problems during feeding, vomiting, jaundice, renal and respiratory disorders. 12 In this case, the patient presented a stable clinical picture, without physical alterations, absence of jaundice and satisfactory suction.…”

Perinatal diagnosis and management of oropharyngeal fetus in fetu: A case report

“…5 Regardless, it is widely accepted that a high level of organogenesis is present in fetus in fetu. 12,18 It is most commonly diagnosed after birth in children younger than 18 months of age 16,19 and is located in the retroperitoneal space in 80% of cases. Findings include a vertebral column in 91% of cases, limbs in 82.5% of cases, central nervous system in 55.8% of cases, gastrointestinal tract in 45% of cases, and genitourinary tract in 26.5% of cases.…”

“…17 Fewer than 200 cases of fetus in fetu have been reported in the literature since it was first described by Johann Friedrich Meckel in the late 18th century. 12,18 It is most commonly diagnosed after birth in children younger than 18 months of age 16,19 and is located in the retroperitoneal space in 80% of cases. 20,21 Unusual locations of fetus in fetu have been reported in the cranium, 8,9 oropharynx, 13 thorax, 21 sacrum, 10 and genitalia.…”

Accessory Penis and Scrotum in a Male Infant

“…6 The most common site of FIF is the retroperitoneum. 6,7 Unlike teratoma, which often occurs in the lower abdomen and pelvis, FIF generally occurs in the upper abdomen, and vertebral column and limbs often can be seen in these fetuses. 7 Because some FIFs lack a spinal column as noticed in this case, investigators have suggested that FIF is a type of highly differentiated teratoma.…”

“…6,7 Unlike teratoma, which often occurs in the lower abdomen and pelvis, FIF generally occurs in the upper abdomen, and vertebral column and limbs often can be seen in these fetuses. 7 Because some FIFs lack a spinal column as noticed in this case, investigators have suggested that FIF is a type of highly differentiated teratoma. 8 However, it is necessary to differentiate between FIF and teratoma because of a slight risk of malignancy associated with retroperitoneal teratomas.…”