Adventitial Layer Enlargement Correlates with the Percentage of Medial Thickness in Peripheral Pulmonary Arteries from Patients with Congenital Heart Defects

Arterial walls undergo modifications during the course of pulmonary hypertension, particularly in the medial and intimal layers, leading to progressive occlusion of the lumen. Adventitial layer enlargement has been described as being present in the experimental hypoxic model and in the persistent pulmonary hypertension of the newborn. It was suggested that this enlargement may be related to stimulating factors derived from the medial smooth muscle cells. This study was designed to verify if different degrees of medial hypertrophy are correlated to the volume density of the adventitial layer in pulmonary hypertension secondary to congenital heart defects. Reviewing 21 lung biopsies from patients with congenital heart defects, we concluded that there is a statistically significant positive linear correlation between the mean percentage of medial arterial thickness and the volume density of the adventitial layer in the biopsies showing isolated medial hypertrophy. On the other hand, in biopsies showing frequent intimal proliferative lesions and irregular medial layer hypertrophy the correlation coefficient was lower. These findings suggest that the adventitial layer participates in the arterial remodeling process in secondary pulmonary hypertension, and that its enlargement depends on the qualitative degree of pulmonary vaso-occlusive disease.