Structure and pathogenesis of plexiform lesion in pulmonary hypertension.

Plexiform lesions are a characteristic vascular change of pulmonary arteries in pulmonary hypertension. Autopsy of lungs from 28 patients with primary pulmonary hypertension were examined to clarify the nature of the plexiform lesions. Histological studies showed that the plexiform lesions, were usually related to fibrous occlusion at the peripheral sites of pulmonary arteries. To clarify the topographic correlation between the arterial occlusion and plexiform lesions a three dimensional analysis of the pulmonary arteries was performed with a computerized image analyzer. The plexiform lesions were located in the small supernumerary branches which were raised at more proximal sites than the occlusive lesions of their parent pulmonary arteries. An electron microscopic study demonstrated that the arterial branches were severely injured and developed into aneurysm-like dilatation with organization. Within the organized arterial branches, endothelial cells proliferated to form complicated capillary-like channels, which is a feature of the plexiform lesion. From these findings the following process may be considered in pulmonary hypertension: the occlusive changes of peripheral pulmonary arteries may induce a by-pass in the proximal supernumerary branches which are severely affected by increased shear stress and ultimately organized. As a result of the organizing, proliferation of endothelial cells may produce plexiform lesions in the special branches of pulmonary arteries.