Conventional tomographic hilar anatomy emphasizing the pulmonary veins.

The pulmonary hili are a frequent site of interpretive uncertainty because of their complex anatomy. The right hilar shadow relates primarily to the ascending and descending pulmonary arteries and the right superior pulmonary vein, whereas the left hilar density accrues from the left pulmonary artery, left descending pulmonary artery, and left superior pulmonary vein. The right and left superior pulmonary veins are intimately associated with and inseparable from the arteries. Knowledge of the course of these veins facilitates their identification on conventional tomograms. The right and left inferior pulmonary veins lie behind the lower hili and contribute only a small increment to the normal hilar density; the horizontal course of these vessels readily distinguishes them from the vertically oriented lower lobe arteries. Prominence of both the right and left superior and inferior veins may cause hilar pseudotumors. Conventional tomograms are most helpful in understanding plain radiographs. A multiview approach in anteroposterior, 55 degrees posterior oblique, and lateral projections is recommended for a complete assessment. Computed tomography in transaxial sections adds further understanding of spatial relations in the hili, including the contributions of the pulmonary veins.