Imaging in pulmonary hypertension, part 2: Large vessel diseases

Pulmonary hypertension is defined by physiological parameters but there are numerous causes that differ in their pathogenesis, management and prognosis. Causes include chronic cardiac or pulmonary diseases and diffuse small vessel disease but also a range of large vessel obstructive diseases. The physiological manifestation of all these diseases is increased pulmonary vascular resistance and pulmonary arterial hypertension, and while clinical features may provide a clue to diagnosis, imaging plays a fundamental role in establishing a precise diagnosis and therefore guiding therapy. Chronic thromboembolic pulmonary hypertension (CTEPH) is the most common large vessel cause of pulmonary hypertension. It is increasingly recognised as a major cause of morbidity and mortality which is underdiagnosed and often diagnosed late. The importance of CTEPH is that for patients in whom the distribution of disease lies predominantly in the proximal vasculature there is potential for symptomatic and physiological cure by surgical pulmonary endarterectomy. More distal disease may be suitable for medical management. Increased awareness on behalf of both clinicians and imagers is therefore paramount. However, there are other rare causes or large vessel obstruction/stenosis such as large vessel vasculitis, pulmonary artery tumour, fibrosing mediastinitis, congenital stenosis or extrinsic compression of the pulmonary arteries/veins. Atypical imaging appearance such as unilateral central pulmonary artery obstruction should lead to consideration of a diagnosis other than CTEPH.