Figure 3e. Chronic pulmonary embolism in a 55-year-old man. (a) Chest radiograph shows enlargement of the central pulmonary arteries along with cardiomegaly. (b) Contrast-enhanced pulmonary CT arteriogram (1.25-mm collimation) obtained at the level of the bronchus intermedius shows eccentric thrombus along the medial margin of the narrowed right interlobar pulmonary artery (arrows). (c) Perfusion lung scan (right posterior oblique view) obtained after administration of Tc-99m macroaggregated albumin shows multisegmental defects, which did not match the findings seen on a ventilation lung scan obtained with Tc-99m Technegas (not shown). (d) Pulmonary arteriogram shows abrupt cutoff in rounded fashion (pouching defect) of the lower lobar arteries (arrow). (e) Photograph of the thromboembolectomy specimen shows organized emboli filling the enlarged central pulmonary arteries. Note how the central thrombus is organized in concave fashion, creating a pouching defect (arrows).