Case of cephalothoracopagus conjoined twinning in an embryonic mouse

BACKGROUND Cephalothoracopagus twinning is extremely rare, and it is characterized by fusion of the head and thorax, two separate spines, pelves, and fore- and hindlimbs. CASE: In this case study, we describe cephalothoracopagus twinning in an embryonic mouse displaying a large but exencephalic head, median facial cleft, a single eye, and a second hindbrain rotated roughly 90° from a second spinal cord. There is a bony connection joining the clavicles, resulting in merged asternal thoracic cavities containing two hearts and four lungs. The abdominal cavities contain double caudal digestive tract structures, but a single esophagus and stomach. CONCLUSION There are several proposed theories regarding the mechanism of spontaneous conjoined twinning; however, the specific mechanisms are still largely unknown. In this report, we highlight the morphological features in a murine example of cephalothoracopagus twinning, furthering our understanding of this rare occurrence while also demonstrating developmental morphogenesis consistent with that reported for human conjoined twins. Birth Defects Research (Part A) 97:421–424, 2013. © 2013 Wiley Periodicals, Inc.