Fetus in Fetu, a Two-case Presentation: Differential Diagnosis and Literature Review

Abstract

Introduction. Fetus in fetu is a rare congenital condition that has been defined as the presence of one monozygotic twin, in most cases, in the sibling’s abdomen. It is most frequently present as a retroperitoneal mass. The diagnostic difference between fetus in fetu and teratoma is discussed. This work’s objective is to describe the case of two patients with fetus in fetu through a reduced literature review in terms of etiologic hypotheses and diagnostic methods. Case Reports. Two cases are presented. The first case is that of an infant with persistent abdominal distension, in whom an abdominal mass was found by palpating. The second case is that of a newborn baby with a prenatal abdominal mass diagnosis. Both cases present X-ray images that demonstrate an abdominal mass compatible with fetus in fetu, reason why the patients were subsequently surgically intervened to remove the mass. Discussion. It is important to keep this pathology in mind as a differential diagnosis of abdominal masses in infant patients, since being able to differentiate it from a mature teratoma would indicate that the mass is an embryonic development alteration, not a tumor pathology. Imaging methods and, in some cases, chromosome or histopathological analyses, are necessary for this, in order to clarify the diagnosis of fetus in fetu. Conclusion. Fetus in fetu is a rare pathology with few cases diagnoses prenatally. It is mainly diagnosed during infancy. X-ray images and, in some cases, chromosome or histopathological analyses, are greatly important for definitive diagnoses.