Figure 2b. (a-d) Transverse contrast-enhanced cephalocaudal contiguous CT scans obtained at mediastinal window settings (width, 400 HU; level, 26 HU; 10-mm collimation) reveal an enlarged left main pulmonary artery (small arrow in b and c), but the mediastinal portion of the right pulmonary artery is completely absent. The interlobar portions (large arrow in c and d) of the right and left pulmonary arteries are depicted, but the right is diminutive compared with the left. Prominent regions of extrapleural fat (white arrowheads in a and b) contain enlarged, contrast-enhanced intercostal collateral vessels (black arrowheads in a and b); this finding of extrapleural fat accounts for the appearance of pleural thickening on the chest radiograph.