Prenatally detected fetus in fetu with progressive imaging organization: Multimodality radiology-pathology correlation

Fetus in fetu is a rare congenital anomaly that may mimic other suprarenal masses including neuroblastoma, teratoma, or adrenal hemorrhage. We present a case of prenatally detected fetus in fetu recognized at 26 weeks gestation as a cystic suprarenal mass. Serial imaging with fetal ultrasounds and MRI at 29 weeks and follow-up ultrasound at 34 weeks demonstrated progression from a nonspecific cystic mass to a lesion with increasing internal organization. Postnatal MRI demonstrated a vertebral axis, a highly characteristic feature of fetus in fetu, and the diagnosis was confirmed by surgical pathology and postoperative radiography. The infant had an uncomplicated postoperative course. This case highlights the value of serial prenatal imaging in demonstrating progressive organization and eventual recognition of a vertebral axis, assisting in distinction of fetus in fetu from other fetal suprarenal masses and guiding appropriate treatment.