Absence of a Primary Division of the Pulmonary Trunk

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Abstract
An ontogenetic theory is proposed to explain the absence of a primary division of the pulmonary trunk on the basis of an error in the septation of the truncus arteriosus, and the two common varieties of the syndrome are discussed in detail. It is suggested that: Both lateral pulmonary arteries are present in this syndrome, but one of them arises anomalously from the systemic circulation. The aberrant origin of one lateral pulmonary artery derives from the dorsal shifting of one of the two ridges responsible for the septation of the truncus arteriosus. The sixth arch on the side of the dorsorotated truncal ridge then becomes incorporated into the newly formed ascending aorta. The combination of tetralogy of Fallot, right aortic arch, and absent left primary pulmonary division results from a single primordial error: a dorsorotation of the left ridge extending throughout the truncoconus. The initial portion of the aberrant (systemic) pulmonary artery may obliterate postnatally, thus impairing maturation of the terminal portion. This would explain the frequent failure to demonstrate the artery by angiography and, occasionally, at dissection.