Venous and arterial changes in pulmonary veno-occlusive disease, mitral stenosis and fibrosing mediastinitis

The pathogenesis of pulmonary veno-occlusive disease (PVOD) is not known. T he diagnosis of PVOD frequently relies on its histological changes since it is often difficult to distinguish clinically from primary pulmonary hypert ension. This study carried out a systematic analysis of the pulmonary venous and ar terial remodelling that occurs in PVOD (n=5) and compared these changes to two other diseases affecting the pulmonary veins, mitral stenosis (MS; n=6) and fibrosing mediastinitis (FM; n=2), using established morphometric tech niques. In PVOD, pronounced intimal and adventitial thickening were noted in veins of all sizes and arterialization of veins >50 mu m external diameter was fo und. Similar changes were evident in the arterial wall, but intimal thicken ing was less severe than in the veins and medial thickening was more pronou nced in arteries <300 mu m external diameter. Eccentric intimal fibrosis of the veins was also noted for the first time in PVOD, although this feature occurred less frequently (approximately one third) than in MS. Less pronou nced structural remodelling was also encountered in the veins in cases of M S and FM, The severity of the venous changes in PVOD may aid its diagnosis and lend insight into its pathogenesis, However, the similarity of the vasc ular changes in each form of venous hypertension also suggests that patholo gy alone may not always differentiate between these disease states. The similarity of the vascular changes in the three forms of venous hyperte nsion suggests that, as in pulmonary artery hypertension, pressure, per se, is one of the triggers to vascular remodelling.