Volume Loss

Atelectasis is one of the most frequently encountered imaging abnormalities on chest radiography and CT, with different implications when detected in hospitalized patients as compared to those encountered in the outpatient setting. Bedridden and postoperative patients often have a dependent type of atelectasis, whereas lobar atelectasis detected in an outpatient is often a harbinger of underlying malignancy (e.g. lung cancer). Medical malpractice cases are sometimes based on the missed diagnosis of lung cancer manifesting as atelectasis and misinterpreted by a radiologist. It is imperative that radiologists be familiar with the direct and indirect imaging signs of atelectasis, as well as the classic patterns of lobar atelectasis. Specific signs of lobar atelectasis will be described including the S sign of Golden and the luftsichel sign. A confident knowledge of lung anatomy, particularly with regard to hilar anatomy and the normal appearance of mediastinal contours and the interlobar fissures, will enable the radiologist to confidently diagnose atelectasis and narrow the differential diagnostic considerations.