Microvascular disease in chronic thromboembolic pulmonary hypertension: the story continues.

In their 1993 report, MOSER AND BLOOR [1] described an array of microvascular ‘‘pulmonary hypertensive’’ lesions in patients with operable chronic thromboembolic disease. Although it was concluded that these findings in any one patient did not ‘‘preclude a positive haemodynamic and clinical result’’, these early observations became the foundation of our current understanding of the evolution of pulmonary hypertension and right heart failure, following the establishment of proximal vessel, occlusive organised thromboembolic disease [2, 3]. Despite the significance and role of the microcirculation in chronic thromboembolic pulmonary hypertension (CTEPH), our understanding of the histopathology remains rather rudimentary [4] and previously confined to descriptions of the precapillary pulmonary circulation [5, 6]. Accordingly, the report from DORFMÜLLER et al. [7] in the current journal is a timely re-examination of this subject. In their report, the authors included analysis of the native lungs from 16 select patients with CTEPH receiving lung transplantation and in one case through an autopsy. This combined series consisted both of CTEPH cases deemed inoperable (n58) and CTEPH patients with residual pulmonary hypertension after pulmonary endarterectomy (PEA) (n59). In addition to previously reported defects seen in the pulmonary arteries, they discovered abnormalities in the capillary bed (similar to defects seen in pulmonary capillary haemangiomatosis) as well as the post-capillary circulation with involvement of the pulmonary veins. The observed degree of venous fibrosis/remodelling and haemangiomatosis-like foci was reported to be of moderate intensity and less pronounced than those seen in pulmonary veno-occlusive disease. Nevertheless, this represents a unique histopathologic description of capillary and post-capillary defects in CTEPH, and widens our awareness of the spectrum of microvascular defects in this form of pulmonary hypertension.