Fetus-in-fetu: a rare condition that requires common rules for its definition
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Fetus‑in‑fetu: a rare condition that requires common rules for its definition Rami Mohamed Bakr Barakat1 · Simone Garzon2 · Antonio Simone Laganà2 · Massimo Franchi3 · Fabio Ghezzi2 Received: 11 January 2019 / Accepted: 8 March 2019 © Springer-Verlag GmbH Germany, part of Springer Nature 2019
Keywords Fetus-in-fetu · Parasitic twin · Fetiform teratoma · Definition Fetus-in-fetu (FIF) is a rare clinical condition that was firstly described by Meckel in 1800, and less than 200 cases have been reported so far [1]. Although adult cases were already described, FIF is typically a pediatric condition managed after birth in children younger than 18 months of age, with symptoms and signs primarily related to its mass effect [2]. Nevertheless, the development of obstetric ultrasonography allowed to anticipate the diagnosis as early as 21 weeks of gestation. Although the definitive diagnosis is performed after surgery, ultrasonography, radiography, computedtomography and magnetic resonance imaging play a key role in the prenatal diagnosis of FIF [3, 4]. This rare condition is considered part of monozygotic twin pregnancies spectrum, and it is supposed to derive from an unequal division of the totipotent inner cell mass of a developing blastocyst. In details, the small cell mass develops within the developing embryo in the vestigial remnant, representing the co-twin in a diamniotic monochorionic pregnancy incorporated within the normal co-twin’s body [3]. We take the opportunity to describe a case recently observed in our practice, aiming to discuss different definitions of FIF based on anatomical and embryological criteria. As occurred in our case (Fig. 1), FIF appears as a mass typically located in the abdomen in the retroperitoneal area (80%), although cases were reported located in the head, sacrum, scrotum, mediastinum, lung, and kidneys [1]. * Antonio Simone Laganà [email protected]; antoniosimone.lagana@asst‑settelaghi.it 1
Fetal Care Clinic of Asyūṭ, Asyūṭ, Egypt
2
Department of Obstetrics and Gynecology, “Filippo Del Ponte” Hospital, University of Insubria, Piazza Biroldi 1, 21100 Varese, Italy
3
Department of Obstetrics and Gynecology, AOUI Verona, University of Verona, Verona, Italy
Among FIFs, the organogenesis of the parasitic mass may have various degrees of development, depending on the three differentiated germ layers (Fig. 2): vertebral column was described in 91%, limbs in 82.5%, central nervous system in 55.8%, gastrointestinal tract in 45% and genitourinary tract in 26.5% of cases [2]. FIF is prenatally differentiated from highly organized teratoma (which carries a slight risk of malignancy) by the spatial organization (cranio-caudal, anterior–posterior and lateral/symmetric development) that can be demonstrated by the presence of vertebral bodies. The visualization of the vertebral column indicates that fetal development reached the stage of notochord. On that basis, Willis [5] proposed the presence of vertebral column as necessary to differentiate FIF fr
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