ABSTRACT
An 83-year-old woman was suspected to have lung cancer in the right lung. However, diffuse opacities only appeared in the left lung, and she was urgently hospitalized due to severe respiratory failure. The opacities in the left lung deteriorated, and she died despite treatments including antibiotics and steroids. An autopsy revealed pleomorphic carcinoma in the right upper lobe, stenosis of the right pulmonary artery due to compression of the right hilar lymph nodes, and diffuse alveolar damage (DAD) throughout the left lobes. Acute respiratory distress syndrome (ARDS), of which a histological feature is DAD, consists of bilateral opacities in the lungs according to the definition. Unilateral ARDS is extremely rare and has reportedly developed in patients with unilateral pulmonary artery agenesis. The unilateral absence of pulmonary perfusion might be involved in the pathogenesis of unilateral ARDS. In patients with lung cancer, compression of the pulmonary artery may result in unilateral ARDS.