Abstract
A rare case of extensive in situ central pulmonary artery thrombosis in primary pulmonary hypertension (PPH) is presented. The differentiation from chronic thromboembolic pulmonary arterial hypertension (CTEPH) is of paramount importance because of different therapeutic strategies. In this case, the presence of mural thrombus in the central pulmonary arteries on computed tomography made the distinction difficult. However, the possibility of in situ thrombosis was suggested on the basis of absence of other findings of CTEPH (abrupt narrowing/truncation of segmental arteries, variation in size of segmental vessels, arterial webs, mosaic attenuation, pulmonary infarcts, and dilated bronchial arteries), and this was confirmed on final pathology.