Multimodal imaging of a double Fetus-in-fetu: a case report

Abstract

Fetus-in-fetu (FIF) is a rare pathology. Published cases usually describe a single fetus, with multiple fetuses being less frequent. This case report describes the findings by ultrasound (US), non-contrast computed tomography (NCCT), and magnetic resonance imaging (MRI) of a double FIF in a 7-month-old male infant with a retroperitoneal mass. Abdominal and pelvic US examination showed a retroperitoneal mixed mass with calcifications and adjacent soft tissue. NCCT of the abdomen and pelvis showed a mixed cystic and solid mass. Two vertebral axes with anencephaly and long bones suggesting two fetuses separated by a thick, complete septum. There was asymmetry in structure differentiation, and one of the fetuses was more developed. Spleen, colon, and left kidney displacement in the host was observed. MRI showed two cavities with double FIF. A 10 × 12 × 10 cm mass was excised by laparotomy. Macroscopic examination showed two anencephalic fetuses with skin and long hair. The lower extremities had distal digitiform formation corresponding to the feet and toes. A diagnosis of double FIF was made. Histopathologic examination ruled out malignancy. This case report is the first of a double FIF in Mexico. Multimodal imaging findings are presented for educational purposes.

Keywords

• Fetus. Fetus-in-fetu. Retroperitoneal space. Infant. Multimodal imaging. Case report.