Fetus in Fetu: A Rare Congenital Anomaly Diagnosed Postnatally by Ultrasonography and MRI

Abstract

Fetus in fetu (FIF) is a rare congenital anomaly with two controversial theories regarding its embryogenesis. Although it is an extremely rare condition, it should be kept in mind as a differential diagnosis while evaluating children with abdominal calcification. Radiological findings on postnatal days 2 and 5 of a neonate with an antenatal scan showing an abdominal mass in the fetus are described here. Ultrasonography and magnetic resonance imaging (MRI) revealed the mass in which the contents favored a diagnosis of the FIF. Characteristic features of FIF on MRI have been less explored and knowledge regarding the same will be of immense help to the radiologist. Complete surgical excision followed by histopathology confirmed the diagnosis.

Keywords: abdominal ultrasonography; fetus-in-fetu; mri - magnetic resonance imaging; pediatric teratoma; preoperative diagnosis.

Figure 1. Ultrasound findings taken on postnatal day 2 demonstrated a heterogeneous complex mass with solid echogenic (red solid circle) and cystic anechoic components (red arrow). Osseous elements and linear echogenic areas with posterior acoustic shadowing were also noted within the mass (yellow arrow).

Figure 2. Coronal (a) and axial (b) TRUFI and coronal HASTE (d) 1.5 T MR images of the abdomen showed a well-defined, lobulated, intra-abdominal retroperitoneal mass in the left suprarenal region with mixed high and low intensities and predominant cystic consistency. T2 hypointense areas resembling fetal parts (limbs, head, abdomino-thoracic cavity) were seen within the lesion (green arrow). Coronal HASTE (c) image showed the mass abutting the left kidney (blue arrow) and spleen.

TRUFI - True Fast Imaging with steady-state-free precession HASTE - Half-Fourier acquisition single-shot turbo SE

Figure 3. Gross specimen findings showed a fetus with an attached umbilical cord (red arrow) and placenta (violet arrow).

Figure 4. Microscopic examination findings showed cartilage and bone (a), skin with appendages (b), gastric tissue (c), and glial tissue (d).