Nodules resembling arachnoid villi in pulmonary venules in plexogenic pulmonary arteriopathy.

We have found nodules histologically resembling arachnoid villi adjacent to pulmonary venules in a woman of 30 years with primary pulmonary hypertension. Such lesions have been reported previously in cases of mitral stenosis and pulmonary thromboembolism and we believe them to absorb excess water from the interstitial tissues of the alveolar walls, thus protecting the lung from the development of edema. In this way they seem to have a similar function to that of cerebral arachnoid villi and granulations which transport cerebrospinal fluid into the dural sinuses.