The included twin or fetus in fetu. A case report.

Abstract

An included twin (fetus in fetu) is a rare and curious anomaly. It is frequently confused with a teratoma. The included fetus has a vertebral column (having passed through a primitive streak stage) and evidence of organogenesis, without neoplastic type of growth or malignant potential. Teratomas, on the other hand, lack a vertebral column (not having passed through a primitive streak stage) and the organogenesis of a fetus in fetu but do manifest some degree of progressive unco-ordinated growth, i.e., they may grow faster than the tissue from which they are derived, and they may undergo malignant change (4, 5, 7). Willis is very definite in his position that teratomas and included twins are distinct and unrelated anomalies: “It is, I believe, a mistake to suppose that a gentle series of gradations exists between double monsters and malformed twins on one hand and teratomas on the other—a mistake widely promulgated because of a prevalent view that teratomas are included monsters or malformed twins. The sooner this misconception is abandoned the better” (7). Lord, in her report on this subject, stated that “proof of the genuinely fetal nature of any specimen of presumed intra-abdominal fetus in fetu or ‘included twin’ requires at least the unequivocal radiographic or dissectional demonstration of part or the whole vertebral axial skeleton, a demonstration which will be reinforced if other appropriately situated bones or organs are shown to be present” (5). She listed in her article of 1954 9 previously reported cases of fetus in fetu and added 2 others (4). Since that time another has been reported by Lewis (3). We believe the following case meets the above criteria. Case Report A white female infant was the first child of a diabetic mother. The diabetes had been controlled by diet and Orinase. The gestation and birth were uneventful and the child weighed 6 lb. 10 oz. The pediatrician was present at the time of delivery, and on his initial examination of the child, he noted a 5 × 7 cm. mass that almost entirely filled the left upper and lower quadrants. A clinical diagnosis of a neuroblastoma, Wilms's tumor, or hydronephrotic kidney was made, and portable films of the abdomen were obtained at one hour of age. These revealed numerous identifiable fetal bony parts, and a radiographic diagnosis of an included twin was advanced. Subsequent intravenous pyelograms were obtained (Fig. 1). At seven hours of age the child was taken to the operating room, and a fetus in fetu, which was retroperitoneal, medial to the duodenum, behind the pancreas, and in front of the left kidney, was removed. The mass was not attached to any structures, and was dissected away without difficulty. It had no identifiable vascular pedicle but was fed by numerous small vessels. Examination revealed the mass to be encapsulated in a thin sac.