Fetus In Fetu Appearing as a Prenatal Neck Mass

Fetus in fetu is a rare congenital abnormality in which a nonviable, parasitic fetus grows within the body of its twin. A fetus in fetu is differentiated from a teratoma because it contains vertebral segmentation, organogenesis, or both.' Fewer than 100 cases of fetus in fetu have been reported, most of which have been in the abdomen. We describe a case of fetus in fetu arising in the neck. Our case is unique because, to our knowledge, a case of fetus in fetu in the neck has not been reported previously. The imaging studies presented include prenatal ultrasound imaging and magnetic resonance imaging (MRI) and postnatal computed tomography (CT).