Fetus in fetu--diagnostic criteria and differential diagnosis--a case report and literature review.

Fetus-in-fetu (FIF) is a rare congenital condition in which a vertebrate fetus is incorporated within its twin. The authors report the case of a newborn boy with prenatal ultrasonographic diagnosis of intraabdominal mass, provoking compression of the left kidney. Plain abdominal radiography, ultrasonography, and computer tomography showed a cystic mass containing multiple calcifications. Pathologic examination showed an irregular fetiforme mass, weighing 8 g, attached to an amniotic sac by a rudimentary umbilical cord with 2 rudimentary limbs, vertebral bodies, encephalus, coroidal plexus, stomach, duodenum, bowel, adrenal glands, upper and lower respiratory tissue, spleen, lymphoid tissue, single cavity heart, and kidney. Molecular analysis using an informative genetic marker, for uniparental isodisomy of chromosomes 14 and 15 showed no genetic difference between the host infant and the fetiform mass. Serum alpha-fetoprotein was < or = 16.000 UI/mL (reference values for age, 4 to 18.9904 UI/mL) before surgery and 8.364 UI/mL after surgery.