Conjoined twin piglets with duplicated cranial and caudal axes.

Background: Twins with doubling of the cranial and caudal poles, yet having a single thorax, are rare.

Methods: One set of diprosopus, dipygus porcine conjoined twins was studied.

Results: In addition to the conjoining anomaly, these twins also exhibited ambiguous internal reproductive features. The twins had two snouts, three eyes, a single thorax, and were duplicated from the umbilicus caudally. Radiography indicated a single vertebral column in the cervical region. The vertebral columns were separate caudally from this point. There was a total of six limbs--one pair of forelimbs and two pairs of hindlimbs. Many medial structures failed to develop in these twins. Medial cranial nerves V-XII were absent or displaced although apparently normal laterally. The medial palates were present but shortened, whereas the medial mandibular rami had folded back on themselves rostrally to form a midline mass between the two chins. Each twin had only one lateral kidney and one lateral testis. Medial scrotal sacs were present but devoid of a testis. There was a midline, "uterine"-like structure which crossed between the twins. However, histological analysis of this structure revealed it to be dysplastic testicular tissue.

Conclusions: The relationship between the abnormal reproductive features in these twins and the conjoining is unclear. The anatomy of these twins, in addition to the literature reviewed, illustrates the internal anatomical heterogeneity of grossly similar conjoined twins. A review of the literature also suggests that conjoined twinning may be more common in swine than was previously suspected.