Consolidation of lung tissue due to alveolar collapse presents some distinctive characteristics, the most common one being the appearance of "plate-like" densities, so described because they resemble inverted dinner plates. Atelectasis shows long, linear densities which are associated with collapsed lung tissue. Atelectasis is most commonly associated with the lower lobes and, to a lesser degree, the middle lobes. A collapsed lobe of the lung can cause shifts in normal lung configuration. The hemidiaphragm may be elevated, the trachea and mediastinum shifted toward the affected side, and the hilum shifted up or down, depending on the location of the atelectasis relative to the hilum.