Myointimal plaques in pulmonary vascular sclerosis associated with interstitial lung fibrosis.

In interstitial fibrosis of the lung, pulmonary vessels show priminent sclerotic changes. We have studied arteries in lung biopsies from patients with lung fibrosis of varied etiology using light and electron microscopy. It was found that the sclerotic change is essentially confined to arteries within fibrotic areas, areas of "nonfibrotic" lung having vessels with no intimal thickening. The changes are most striking in arteries with an external diameter of 500 micrometer. or greater (p less than 0.001), although smaller sized vessels also show significant changes. Ultrastructurally, the plaques are composed of typical smooth muscle cells with basement lamina, pinocytotic vesicles, dense bodies, and cytoplasmic microfilaments. These arterial changes could result from damage to the blood vessel which accompanies the mechanism producing lung fibrosis. Alternatively, the myointimal change could conceivably be part of an adaptive response following the establishment of fibrosis. In either instance, the narrowing would decrease blood flow to physiologically disadvantaged areas of the lung, and the muscle fibers might play an active role in reducing the blood flow.