HISTOLOGIC-STUDY OF THE SMALL PULMONARY-ARTERIES IN 38 PATIENTS WITH PULMONARY ATRESIA AND INTACT VENTRICULAR SEPTUM

The structure of the small pulmonary arteries was studied during autop sies performed on 38 patients with pulmonary atresia with intact ventr icular septum. The thicknesses of the media of these small pulmonary a rteries measured using a quantitative morphometric method varied widel y. However, there was a notable tendency toward thinning of the media, especially in neonates. In cases in which the patient had undergone p rostaglandin El treatment, the media was thinner, which suggests that the longer the treatment, the thinner the media. Intimal lesions were observed in 18 of the 38 patients (47%), including 12 of the 22 neonat es (55%). Intimal lesions were also found in the patients with thinner media. Based on these results, we propose that organized thrombus for mation and intimal proliferation are more likely to develop in patient s with reduced pulmonary blood flow, such as in those with pulmonary a tresia and intact ventricular septum. In prostaglandin-treated patient s, an imbalance between the markedly thinner median muscle and the rel atively higher pulmonary blood flow and pressure may contribute to fib rous intimal proliferation. Small pulmonary arteries with a strikingly thinner media may be vulnerable to higher pressure, predisposing the patient to the development of intimal lesions.