Craniorachipagus symmetric conjoined twinning: Identification of a fourth case and delineation of the phenotype.

Symmetric craniorachipagus is a type of bi-umbilical conjoined twinning, to date represented by four confirmed cases that share a similar phenotype. This includes dorsal conjunction at the sides of the occipital craniums and the vertebral columns, in the absence of any visceral connections. Details on its etiopathogenesis and apparent lethality await additional case investigations. No unequivocally confirmed cases of symmetric rachipagus without cranial involvement have been reported and its existence in humans has yet to be proven.