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Figure 3c. Spiral CT scans obtained in a 41-year-old patient with previous history of recurrent left upper lobe hemoptysis. (a) Spiral CT scan (2-mm collimation, pitch of 2, 30% iodinated contrast agent, scanning delay of 15 seconds) obtained at the level of the left main bronchus shows the nonopacification of a small left interlobar pulmonary artery (arrow). Note the mediastinal shift to the left due to a small left lung. (b) Spiral CT scan obtained at the same level during the same session with a longer scanning delay (scanning delay, 22 seconds; other parameters same as in a). The opacification of the left interlobar pulmonary artery (arrow) at the systemic phase confirms that the focal hypoattenuation previously observed was related to retrograde left-to-right shunting, itself related to left pulmonary venous atresia. Note the enlargement of bronchial and intercostal arteries (arrowheads) and extensive left pleural thickening. (c) Stacking of eight 2-mm-thick sections of the right lower lobe from the same data set demonstrates an additional atresia of the right inferior pulmonary vein ().