AJR 2002; 179:1481-1483
© American Roentgen Ray Society
Fetus in Fetu: Three-Dimensional Imaging Using Multidetector CT
Seong Sook Hong1,
Hyun Woo Goo1,
Mi Ran Jung1,
Hyun Jin Kim1,
Ellen Ai-Rhan Kim2,
Ki Soo Kim2,
Soo Young Pi2,
Seong Chul Kim3,
Jean-Claude Hoeffel1,4 and
Chong Hyun Yoon1
1 Department of Radiology, Asan Medical Center, University of Ulsan College of
Medicine, 388-1 Poongnap-dong, Songpa-gu, Seoul 138-040, Korea.
2 Department of Neonatology, Asan Medical Center, University of Ulsan College of
Medicine, Seoul 138-040, Korea.
3 Department of Pediatric Surgery, Asan Medical Center, University of Ulsan
College of Medicine, Seoul 138-040, Korea.
4 Department of Radiology, Hôpital Jeanne d'Arc, B.P. 303, 54201 Toul,
France.
Received February 21, 2002;
accepted after revision May 23, 2002.
Address correspondence to C. H. Yoon.
Introduction
Fetus in fetu is a rare abnormality associated with the abnormal
embryogenesis in a diamniotic, monochorionic pregnancy, in which a vertebrate
fetus is enclosed within the body of a normally developing fetus
[1,2,3,4,5,6,7].
Other researchers have described imaging findings on CT, MR imaging, or
sonography
[3,4,5,6,7].
To the best of our knowledge, three-dimensional (3D) imaging findings have
not been reported for fetus in fetu. In our case report of fetus in fetu,
multidetector 3D CT was helpful in delineating the complicated anatomy of this
entity and for defining the blood supply before surgery.
Case Report
A 2-day-old boy, who was born at 37 weeks of gestation with a birth weight
of 3695 g, was referred to neonatology because a cystic mass with
calcification had been found in the right upper abdominal area on prenatal
sonography. The pregnancy was normal, and no family history of twinning or
tumors was known. The neonate was completely asymptomatic.
At physical examination, the mass was firm, smooth, and not tender.
Laboratory findings, including serum 
-fetoprotein and ß-human
chorionic gonadotropin levels, were within normal limits. On radiography of
the abdomen, we identified a craniocaudal arrangement of what appeared to be
two spines and two long bones in the right upper quadrant of the abdomen
(Fig. 1A) and thus suspected
fetus in fetu.
CT was performed before surgery to more clearly define the relationship
between the mass and the adjacent organs. We used a multidetector CT scanner
(QX/i LightSpeed; General Electric Medical Systems, Milwaukee, WI).
Contrast-enhanced CT was performed after IV injection of 4 mL/kg of a mixture
(1:1) of saline and iopromide (Ultravist 370; Schering, Berlin, Germany)
through a 24-gauge angiographic catheter inserted in an antecubital vein via a
power injector at a flow rate of 0.8 mL/sec. The technical parameters included
1.25 mm of collimation, table speed of 3.75 mm, gantry rotation speed of 0.8
sec, 120 kVp, and 40 mA. Postprocessing was performed on a commercially
available workstation (Advantage Windows 3.1; General Electric Medical
Systems). The techniques we used for 3D reconstruction were shaded surface
display, maximum intensity projection, and volume rendering.
Three-dimensional CT scans showed a large well-defined mass enveloped by a
sac in the retroperitoneum that displaced the right kidney posteriorly. The
mass contained both cystic and solid portions. The bony components resembled
vertebral bodies, ribs, two femurs, two humeri, and cartilaginous structures.
The fetuslike structure was anencephalic and had two short upper extremities
and fused lower extremities containing two long bones with toelike structures
(Figs. 1B and
1C). An anomalous blood supply
to the mass arose directly from the right renal artery
(Fig. 1D). Another ovoid
lobulating mass supplied from the right renal artery was present on the inner
surface of the cyst (Fig.
1E).
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Fig. 1B. —2-day-old boy with fetus in fetu. Volume-rendered
three-dimensional CT scan obtained in left anterior oblique plane shows
anencephalic fetuslike structure with multiple bony components of vertebral
bodies, ribs, two femurs, two humeri, and feet.
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Fig. 1C. —2-day-old boy with fetus in fetu. Three-dimensional CT scan
obtained using shaded surface display in which other bony structures are
eliminated shows clearer anatomy of fetuslike structure than can be seen in
B.
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Fig. 1D. —2-day-old boy with fetus in fetu.
Maximum-intensity-projection CT scan shows large well-defined cystic and solid
mass enveloped by sac in retroperitoneum. Note anomalous blood supply to fetus
in fetu from right renal artery (arrowheads) and posteriorly
displaced right kidney.
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Fig. 1E. —2-day-old boy with fetus in fetu.
Maximum-intensity-projection CT scan shows second ovoid lobulated mass
(arrow) within sac. Findings at histopathology (not shown) revealed
multiple pieces of symmetrically arranged cartilage and bone.
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This boy underwent surgical exploration 3 days after birth, and a large
retroperitoneal mass that displaced the right kidney posteriorly was revealed.
As suggested by the 3D CT findings, surgeons found an anomalous blood supply
from the right renal artery to the fetuslike structure. The mass was resected
en bloc. Gross examination revealed the mass to be an anencephalic fetus in
fetu that weighed approximately 185 g and was 7 cm in length. The separate
ovoid mass (
3 cm) contained grossly symmetric pieces of cartilage.
Histopathologic findings showed such extensive autolysis that it was
impossible to determine whether the ovoid mass was another fetus in fetu or a
teratoma. Neither a definite vertebral axis nor well-organized structures were
identified in this second mass, but the cartilaginous tissues were
symmetrically located within it, suggesting early formation of both upper and
lower extremities. A small gutlike structure with mucosal and smooth muscle
wall was also noted. These findings suggested that the small solid mass could
in fact be another fetus in fetu.
Discussion
Fetus in fetu is the result of an abnormality in the twinning process that
results in the formation of the nondominant twin inside the body of the
dominant twin. The growth of a fetus in fetu initially parallels its twin in
the uterus, but it abruptly stops because of the vascular dominance of the
host twin or an inherent defect in the parasitic twin
[1,2,3,4,5,6,7].
Fetus in fetu is always anencephalic, but the vertebral column and the limbs
are present in almost all cases (91% and 82.5%, respectively). The lower limbs
are more developed than the upper limbs. Fetus in fetu has rarely been found
in the central nervous system, gastrointestinal tract, retroperitoneum,
vessels, or genitourinary tract of the host twin; it is even more rarely found
in the lungs, adrenal glands, pancreas, spleen, or lymph nodes
[4,
5].
Some authors believe that teratoma and fetus in fetu are part of a spectrum
of the same disorder, but others have suggested, for several reasons, that
fetus in fetu is a pathologic entity that is distinct from teratoma. An
important feature that has been used to distinguish fetus in fetu from
teratoma is the presence of a vertebral column. Identification of the
vertebral column indicates that fetal development of the included twin must
have advanced at least beyond the primitive streak stage (12-15 days'
gestation) for a notochord, which is the precursor of the vertebral column, to
have developed
[1,2,3,4,5,6,7].
Fetus in fetu generally occurs singly; multiple masses have been found in only
a few instances. In our patient, a mass enveloped by a sac contained a second
mass that was suggestive of a second fetus in fetu.
Imaging plays an important role in the correct diagnosis of fetus in fetu.
This diagnosis can be made on abdominal radiography by identifying a vertebral
column, specific bony structures, or both. Occasional cases have also been
reported in which the spinal column could not be identified on imaging
[1], likely because the
vertebral bodies could not be seen in an underdeveloped and markedly
dysplastic spinal column. Vascular connections to the fetus in fetu have been
reported. The predominant blood supply appears to be derived from the plexus,
where the fetus in fetu and the sac are attached to the abdominal wall. Other
sources of blood supply include the superior mesenteric artery, inferior
mesenteric artery, and middle sacral artery
[1]. In our patient, the fetus
in fetu derived its blood supply from the right renal artery.
The preoperative diagnosis of fetus in fetu was made in only 16.7% of the
cases reported before 1980, which may be explained by the fact that CT,
although performed to some degree before 1980, was not widely available.
Currently, CT is extremely helpful, both for making the diagnosis and in
preoperative planning [1].
Multidetector CT provides high quality images with high spatial resolution and
fewer motion artifacts than single-detector CT. The 3D CT scans obtained in
our patient are preferable to axial CT images for depicting a complicated
lesion with high fidelity. We think that 3D CT provides better images than
those of previously developed techniques. Therefore, 3D CT was helpful in
preoperative planning because the information it provided enabled evaluation
of the relationship of the fetuslike structure to the other abdominal
structures and to its blood supply. To the best of our knowledge, this case is
the first in which the blood supply of a fetus in fetu was identified before
surgery.
In conclusion, 3D CT accurately revealed the detailed anatomy of a
fetuslike structure and depicted its blood supply preoperatively; therefore,
this imaging technique is useful for planning surgical treatment of patients
with fetus in fetu.
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Introduction
Case Report
