Fetus-in-Fetu: A Differential Diagnosis of Neonatal Fetiform Encysted Abdominal Mass

Abstract

Fetus-in-fetu (FIF) is a rare embryological anomaly in which an encysted fetiform mass develops within the infant or adult host body. It mainly occurs intraabdominal. There are embryo-pathogenetic debates over whether it belongs to the spectrum of highly differentiated teratomas or is a parasitic twinning from a monozygotic monochorionic diamniotic pregnancy. The presence of vertebral segments and an encapsulating cyst can reliably distinguish FIF from teratoma. The diagnosis may be initially made by imaging modalities such as computed tomography (CT) and magnetic resonance imaging (MRI), and a confirmatory diagnosis made by histopathology of the excised mass. Our center experienced a case of a male neonate presented after emergency cesarean delivery at 40-week gestation with the suspicion of an intraabdominal mass identified antenatally. Antenatal ultrasonography at 34 weeks gestation suggested the presence of an intraabdominal cystic mass measuring 6.5 cm with a hyperechoic focus. A follow-up MRI performed after the delivery showed a well-defined mass with the cystic formation in the left abdominal region with a centrally located fetiform structure. Vertebral bodies and long limb bones were visualized. The diagnosis of FIF was initially made preoperatively by the characteristic findings of imaging studies. Laparotomy was scheduled on day 6, revealing a large encysted mass with fetiform content. FIF should be considered a possible differential diagnosis of neonatal encysted fetiform mass. Routine antenatal imaging permits more frequent antenatal detection with earlier workup and management.

Infantile fetiform abdominal mass: Teratoma or fetus in fetu? A case report with insights into radiological diagnosis and surgical management

“…The most common location of FIF is retroperitoneum (80%) [ 7 , 8 ]. Other rare locations such as the oral cavity, scrotum [9] , and sacrococcygeal region [1] are also noted.…”

“…The degree of early malignancy may be correlated with the absolute amount of blood AFP, and tracking trends in serum AFP levels can be helpful in tracking tumor recurrence following resection. B-human chorionic gonadotropin (Beta HCG) and, less frequently, carcinoembryonic antigen (CEA) have been used as malignancy indicators for gonadal teratoma [1] .…”

“…Radiological differentiation of these 2 entities should be made because of the difference in surgical planning and treatment options. Features such as visualization of distinct bony vertebral elements and encysted cystic components are the specific features of Fetus in fetu [1] . In contrast, the presence of elevated serum markers can help diagnose teratoma.…”

Fetus In Fetu With Myelomeningocele

“…In contrast, teratomas develop due to disorganized and uncontrolled pluripotent cell replication, and thus, vertebral segmentation and organogenesis are typically absent. 4 To classify a mass as FIF, it must exhibit one of the following features: a mass enclosed within a distinct sac, partially or completely covered by skin, and anatomical features that are recognizable to the naked eye. Additionally, it should be attached to the host by a pedicle containing a few relatively large blood vessels It's crucial to differentiate between FIF and teratoma due to the slight risk of malignancy associated with retroperitoneal teratomas.…”

Fetus in Fetu: A Rare Congenital Anomaly Diagnosed Postnatally by Ultrasonography and MRI

“…Imaging plays a very important diagnosis in diagnosing FIF. There are multiple case reports describing the diagnosis of FIF upon identification of vertebral column in CT in literature; however, reports containing ultrasound and MRI findings are sparse [7,9,11,12,[15][16][17]. Knox et al reported a case of FIF with no evidence of calcification seen within the mass on a plain radiograph [18].…”