Thoracopagus Twins: Prenatal Diagnosis

While the delivery of conjoined twins is one of the rarities of obstetrical practice, the increasing frequency of routine prenatal roentgen studies makes it imperative that the radiologist recognize this anomaly so that he may forewarn the referring obstetrician of the problem to be faced. In as careful a review of the literature as was possible, though admittedly incomplete, only one case (1) was found in which a roentgen diagnosis of conjoined twins was made before delivery; two additional examples (2, 3) have been discovered through personal correspondence. The following case is presented to call attention to several points which may aid in the prenatal roentgen recognition of this developmental anomaly. While the modus operandi in the production of Siamese twins is not conclusively known, a number of theories (4, 5) have been advanced, one or the other of which may be the explanation in any given instance. The best known theory, that of the separation of the two blastomeres formed by the first division of the fertilized egg, may well explain identical Siamese twins but certainly cannot account for dissimilar twins. The dizygotic theory, that two separate eggs are fertilized by two separate sperm and then for some reason fuse, is certainly the least acceptable. On a monozygotic basis, it has been suggested that an unfertilized egg may at times divide equally into two, which are then fertilized by separate sperm. Other possibilities are that the nucleus and a large polar body of a single egg may be fertilized by two different sperm, or that an egg may be binucleate, each nucleus being fertilized by a separate sperm. These latter theories could well explain the fact that conjoined twins may be as unlike as any two siblings. It is interesting that in our case one of the twins had a cleft palate while the other did not. A 25-year-old woman had her last menstrual period on Jan. 4, 1948. She had had one previous pregnancy, in 1943, with delivery of a normal 7-lb. infant after a four-hour labor. The course of the second pregnancy was normal until June 21, when the obstetricians made a diagnosis of polyhydramnios. The uterus was 22 cm. in height on May 31 and 33 cm. in height on July 12. There was beginning edema of the lower extremities on June 21, which progressed to a three-plus generalized edema on July 12. Respiratory distress was evident on about the first of July from the increased intra-abdominal pressure and became rapidly worse until the time of delivery. Because of the polyhydramnios, the obstetricians suspected some type of fetal abnormality and on July 12 referred the patient for roentgen examination. At this time a presumptive diagnosis of thoracopagus twins was made but because of the rarity of the condition the patient was again examined one week later, July 19. A positive diagnosis was then established. Several days later the conjoined twins, thoracopagus in type, were delivered by cesarean section.