Pulmonary artery branches

Normal pulmonary vessels have an adequate caliber and an appropriate distensibility and they provide active support to forward flow by their windkessel function. Pathologic vessels can be either stenotic on different levels of the vessel tree, they can be hypoplastic in segments or in total, or finally vessels can be compressed by other structures like the aorta or bronchi. Hypoplasia can be due to flow restriction by a localized stenosis or can be due to an intrinsic disorder like Williams-Beuren syndrome (WBS). A specially generalized vessel abnormality is present, whenever an aortopulmonary collateral has been unifocalized to the pulmonary vessel tree. From its embryologic origin, these collaterals are more systemic and not pulmonary arteries. In many patients the obstructions in the pulmonary vessels are partially a consequence of surgical or – less often – transcatheter procedures and are caused by the formation of scar tissue or restrictions due to small conduits or stents.