Primary pulmonary hypertension. The risk and benefit of lung biopsy.

In an effort to resolve some of these questions, the National Heart, Lung, and Blood Institute established a registry of patients with PPH, using strict criteria for entry and obtaining extensive initial and follow-up characterization. The data published so far have provided some insights into this disorder, but much remains unknown.3 One unsettled issue is the value of open lung biopsy in PPH. This is a potentially hazardous procedure, and one that may compromise subsequent selection for transplantation. Therefore, establishment of its risk and benefit is of substantial importance. There are at least four potential benefits of open lung biopsy: insights into pathogenesis, guidance of therapy, confirmation (or refutation) of the diagnosis, and establishment of prognosis. In this issue of Circulation, two reports deal with the value of lung histopathology in addressing these questions.4,5 With respect to pathogenetic insights, previous reports have suggested that so-called "plexogenic (plexiform) lesions" and concentric intimal thickening point to pulmonary vasoconstriction as the dominant mechanism, whereas microthrombotic lesions and eccentric intimal thickening indicate in situ thrombosis as the major underlying basis for small vessel obstruction.6-9 In the latter instance, some confusion has resulted from use of the term thromboembolic pulmonary hypertension, even though no evidence exists for an embolic source.