Antenatal oral fetus in fetu with a mandibular defect: A case report

Fetus in fetu (FIF) is a rare congenital condition defined by the presence of a non-viable, malformed parasitic fetus located within the body of a living autosite host twin, most commonly found in the retroperitoneum. The clinical manifestations of FIF vary with the anatomical site. Timely and accurate diagnosis is crucial to prevent significant morbidity in the host twin resulting from the growth of the FIF mass. Comprehensive clinicopathological data regarding FIF remain limited, as existing literature on the subject is sparse. The majority of reported cases have been diagnosed in infancy and childhood. This report presents a particularly rare case of oral FIF, diagnosed antenatally, wherein the parasitic twin was observed as a mass protruding through a midline mandibular defect of its host twin.

A 20-year-old, G3P1A1, presented for her sonography at 22 weeks gestation. A significant midline mandibular defect was noted in the fetus, with a protruding associated mass emanating into the floor of the mouth. Through a multi-imaging approach, FIF was diagnosed. This case report aims to enhance awareness regarding this uncommon developmental entity.

FIF, due to its rarity, can be a difficult case to manage clinically. This case underscores the critical importance of early antenatal sonographic diagnosis, as such identification carries substantial clinical implications and prognostic value.