Muscle abnormalities associated with the twin reversed-arterial-perfusion (TRAP) sequence (acardia)

Even though over 400 acardia (twin reversed-arterial-perfusion, TRAP) specimens have been reported in the literature since 1533, few attempts have been made to provide detailed evaluation of anything other than the circulation. The purpose of this study was to evaluate the various limb defects in nine TRAP specimens in light of the presumed etiology and pathogenesis, reversed arterial perfusion, and subsequent degenerative changes in the fetus. Two hypotheses were tested: (1) degeneration of formed tissues should not result in tissue rearrangement and (2) one tissue type should be lost in preference to the others. Neither of these hypotheses were supported by the data. Alternative explanations are discussed as well as the implications of these observations on the concept of reversed arterial perfusion.