Occlusion of intra-acinar pulmonary arteries in pulmonary hypertensive congenital heart disease.

Lung biopsy specimens from 10 consecutive cases of congenital heart disease and pulmonary hypertension (2 months-6.5 years) were examined by light and electron microscopy. By light microscopy, 8 cases showed a reduction in number of patent alveolar wall arteries associated with the structural features of early pulmonary vascular disease-extension of muscle, a significant increase in pulmonary arterial medial thickness (P less than 0.001) and little if any intimal proliferation (Heath & Edwards Grade I or II). In one additional child with Grade IV disease, arterial number could not be determined accurately. For all 10 cases, all blocks of tissue examined by light and electronmicroscopy showed absence of any lumen in structures identified as alveolar wall arteries by their position, shape and the presence of an external (or single) elastic lamina. In 3 additional similar cases, endothelial cells of narrowed and occluded arteries were marked by labelling with the lectin Ulex europaeus. Occluded arteries were identified consisting of mature smooth muscle cells and remnants of degenerating endothelial cells. Occlusion of alveolar wall arteries appears to be an early event in the development of pulmonary vascular disease, is associated with differentiation of smooth muscle cells in normally thin walled precapillary arteries and precedes significant obliterative intimal changes in more proximal vessels.