Unilateral diffuse lung opacity; Differential diagnosis with emphasis on lymphangitic spread of cancer.

One hundred adults with unilateral diffuse lung opacity have been studied. Seventy cases involve the right lung. Lymphangitic cancer, pneumonia, pulmonary edema, aspiration, and radiation injury account for the majority of cases (90%). Unilateral pulmonary edema is usually right sided, and, frequently, the heart is not enlarged. Unilateral lymphangitic spread of cancer is usually right sided and most often due to a primary lesion in the involved lung. Occasionally a cancer outside the lung may spread unilaterally.