Classical concepts in thoracic radiology - Right hilar pseudomass due to partial right lower lobe atelectasis

In cases of right lower lobe atelectasis, in which the lobe remains partial ly aerated, rotation of the right hilum into an anteroposterior plane can r esult in the formation of a "pseudomass" in the right hilar region on the f rontal radiograph. Failure to recognize this variant appearance of right lo wer lobe atelectasis can result in a false diagnosis of a hilar mass and re sult in an unnecessary workup for lung cancer. Familiarity with this varian t appearance of right lower lobe atelectasis, coupled with careful comparis on with recent normal chest radiographs, should allow a correct diagnosis o f a "pseudomass" in most cases. Computed tomography of the thorax can relia bly exclude a hilar mass in cases in which recent normal chest radiographs are unavailable for comparison.