Multidetector computerized tomography in diagnosis and preoperative workup of fetus in fetu: A case series

Case-1

A two-month-old girl child was presented in the pediatric surgery department with complaints of a lump abdomen with stable vitals and accepting oral feeds. On examination, the mass was non tender. The child was sent to the Department of Radiology for a detailed workup. Plain radiographs suggested long bones within the fetal abdomen. Differential diagnosis included a well-differentiated teratoma or fetus in fetu. To assess the presence of vascularity and further anatomical characterization, an ultrasound sonography (USG) of the abdomen was performed. A detailed ultrasound revealed a large inhomogeneous mass in the retroperitoneum containing both fat and calcification. A CT scan was done to obtain detailed anatomical information and characterization of the anomaly. CT scan revealed a large mass containing a large area of fat and fluid with partially formed spinal curvatures and a well-formed knee joint showing femoral condyle, tibial plateau, and patella. Skull bones were not seen [Figure 1]. No encasement of any major organ was noted; however, gross displacement of the visceral organ without any obvious sign of infiltration was seen. Surgical exploration showed a well-formed fetus covered with skin and lanugo. There were well-formed lower and upper limbs, a spinal canal, and acranic brain parenchyma. Anal dimple was noted, however, genitalia was not developed [Figure 2]. The patient had an uneventful postoperative course following the excision of the fetus in fetu.

Close

Figure 1:

CT scan coronal view bone window showing well-formed femur with patella and tibia forming knee joint contained within well-defined sac along with fat and soft tissue in left hypochondrium and left lumbar region.

Export to PPT

Close

Figure 2:

Postoperative specimen showing soft tissue mass with well-formed skin with lanugo, anal pit, and limbs. Brain parenchyma without calvaria is also noted.

Export to PPT

Case-2

A two-year-old girl was presented with a smooth non tender lump in the abdomen. The child was active and had normal developmental milestones. The parents observed a mild increase in mass within three weeks of birth. Similar protocols were followed as in a previous case and subsequently CT scan was performed. CT scan showed a well-formed area of fat and fluid in the retroperitoneal space in the right lumbar space. A well-formed ankle and tarsal bones were noted, but an ipsilateral kidney was not seen. No spinal canal could be delineated. There was no evidence of upper limbs and skull bones [Figure 3]. Differential of well-differentiated teratoma and fetus in fetu was kept in this particular case. The patient underwent surgical removal of the mass. There was a good correlation of the mass on gross inspection with the preoperative information obtained from the CT scan. Useful information was obtained from virtually reconstructed images during post-processing of images. Gross examination after surgical removal of 1.5 kg parasitic twin showed a well-formed fetus with well-formed appendicular skeleton and skin covering. Anal dimple was noted, but genitalia were poorly developed. Both cases showed a cystic fluid-filled cavity that represented acranic brain parenchyma. Post-operative recovery was good, and the patient was discharged.

Close

Figure 3:

CT scan coronal view bone window showing well-formed ankle joint and metatarsal bones in another case in right hypochondrium.

Export to PPT

CT scan proved to be an excellent modality to delineate fat planes, determining the course of further management and ruling out any malignant transformation and associated anomalies.

DISCUSSION

Fetus in fetu clinically presents as a lump in the abdomen (70%), mainly in the upper retroperitoneum.⁶ Single parasitic fetus is the commonest presentation (88%). The present fetal size was approximately 13 cm x 10 cm. The fetal weight varies between 1.2 kg and 1.8 kg, and it was 1.5 kg in both cases. Cross-sectional imaging helps to rule out all common causes of lump abdomen, except teratoma and fetus in fetu. The presence of a vertebral axis and identification of limbs is characteristic of fetus in fetu and excludes the diagnosis of teratoma.⁷ The organs demonstrated are, namely, spine in 91%, limbs in 82.5%, CNS in 55.8%, GIT in 45%, vessels in 40%, and GUT in 26.5% cases, respectively.⁸ The vertebral column is an important clue that suggests the formation of a notochord, which is an advanced primitive streak stage. A noncalcified vertebral column invisible on a radiograph or a CT scan or its total absence (9%) does not exclude the diagnosis of the fetus in fetu.⁹ In our study, the spinal canal was not identified on the cross-sectional imaging in one of the cases, which turned out to be a fetus in fetu on postoperative gross examination. Most of these fetuses are anencephalic,¹ which was also observed in both our cases. Fetus in fetu gets its blood supply from the rich vascular plexus around the well-formed cyst wall. Vascular pedicle is unusual and observed in large growing masses with delayed presentation.¹⁰ Malignant transformation is rare in the fetus in fetu, and only one case has been reported in literature.¹¹ However, it may increase in size and can cause local mass effects in terms of hemorrhage. The role of imaging is diagnostic, and a CT scan is a valuable modality showing round or tubular fat collection around central bony structures.¹² Surgical excision is the treatment of choice, and gross examination confirms the diagnosis. Our pre-operative and postoperative findings were similar to cases reported earlier in the literature.