“…12,31 More recently, however, there have been reports of sacrococcygeal and perineal fetus in fetu first visualized on ultrasound examinations performed as early as 18 weeks. 22,32 Nevertheless, distinguishing fetus in fetu from teratomas antenatally remains a challenge because both entities can present as soft tissue masses with calcifications. 31 Masses may also be difficult to discern on early ultrasound examinations.…”