Fetus-in-fetu: imaging and pathologic findings

Area of Science:

• Pediatric Surgery
• Medical Imaging
• Pathology

Background:

• Fetus in fetu is a rare congenital anomaly where a malformed parasitic twin is found within the body of its host twin.
• Early diagnosis and surgical intervention are crucial for favorable outcomes in infants with fetus in fetu.

Observation:

• A 3.5-month-old boy presented with an incidentally discovered abdominal mass.
• Physical examination revealed a smooth, firm, nontender mass in the right upper quadrant.
• Abdominal ultrasonography and CT scans demonstrated a large, heterogeneous retroperitoneal mass with identifiable skeletal structures.

Findings:

• Surgical excision of the mass revealed an incompletely developed fetus with discernible external features and a connecting umbilical cord.
• Microscopic examination confirmed the presence of various tissues including skin, cartilage, bone, and intestine.
• Three-dimensional CT imaging was instrumental in identifying key diagnostic indicators like the vertebral column and limb bones.

Implications:

• CT imaging, particularly 3D reconstructions, significantly improves the accuracy of pre-operative diagnosis for fetus in fetu.
• Distinguishing fetus in fetu from teratoma is critical for appropriate management and prognosis.
• This case highlights the importance of advanced imaging in diagnosing rare congenital malformations.