Pathology and aspects of pathogenesis in pulmonary arterial hypertension

Pulmonary Arterial Hypertension (PAH) is a term which has been recently defined at the WHO-meeting in Evian and includes Primary Pulmonary Hypertension (PPH), as well as PAH related to specific pathological conditions. The poor prognosis of the disease seems to be related to a peculiar pathological anatomy, consisting of characteristic lesions of small, muscular pulmonary arteries. In addition to common hypertrophy of the tunica media, other proliferative lesions such as intimal thickening or plexiform lesions are summarized under the term of plexogenic arteriopathy. Moreover, in situ thrombosis and rarely isolated pulmonary arteritis can be observed in lungs of patients displaying PAH. Different pathomechanisms explaining these morphological changes of pulmonary vasculature have been discussed in the past, including endothelial and thrombocytic dysfunction, deregulated vasoconstriction, coagulation abnormalities, or cancer-like growth. Furthermore, latest studies on the importance of inflammatory mediators, so-called chemokines, in the lungs of PAH patients have brought a possible inflammatory component of the disease into consideration. Finally, recent identification of responsible gene mutations in subgroups of patients, as well as latest developments in genetic screening have shed some light into the modus of inheritance. Nevertheless, the role and impact of these different pathomechanisms have yet to be better defined.