Lung expansion in the diagnosis of lung disease.

The most common abnormality detected during thoracic radiography of patients with lung disease is increased opacity of the lungs. Although sensitive for lung disease, this finding alone is not specific for the cause of lung disease. Other conditions that increase lung opacity include technical complications and extrapulmonary lesions that compress the lung. Therefore, other radiographic signs are used to make a more definitive diagnosis. The size of the abnormally opaque lung lobe can be helpful in differentiating lung disease from other conditions. If the lung is normal to large in size, it is considered expanded. This situation always indicates disease. If the lung is small, it is considered incompletely expanded. This finding indicates pulmonary, thoracic wall, or pleural space disease or a technical complication. Common terms that are used to describe the volume of expanded or incompletely expanded lungs include infiltration, consolidation, collapse, and atelectasis. Although they are used as radiographic diagnoses, these terms should not be considered an endpoint analysis, and other radiographic signs must be sought to make a more definitive diagnosis.