High-resolution CT of the lung: determination of the usefulness of CT scans obtained with the patient prone based on plain radiographic findings.

OBJECTIVE: We assessed the usefulness of chest radiographs for predicting whether high-resolution CT scans obtained with the patient prone would be valuable in assessing suspected diffuse lung disease.
MATERIALS AND METHODS: In 100 consecutive patients undergoing high-resolution CT, findings on plain chest radiographs were classified as normal, possibly abnormal, or abnormal. CT scans obtained with the patient supine were assessed for the presence and distribution of lung abnormalities without knowledge of the plain radiographic classification. A second review of the CT scans was done with equal numbers of scans obtained with the patient prone and with the patient supine. The usefulness of the CT scans obtained with the patient prone for detecting lung disease was determined and related to the plain radiographic classifications.
RESULTS: High-resolution CT scans obtained with patients prone were helpful in excluding or confirming posterior lung abnormalities in 10 (28%) of 36 patients who had normal findings on chest radiographs, five (28%) of 18 patients who had possibly abnormal findings on chest radiographs, and only two (4%) of 46 patients who had abnormal findings on chest radiographs. The proportion of patients who benefited from high-resolution CT scans obtained with the patient prone was significantly lower among the patients with abnormal findings on chest radiographs than among the patients with normal (p = .008) or possibly abnormal (p = .02) findings on chest radiographs. The two patients with abnormal findings on radiographs in whom CT scans obtained with the patient prone were helpful had minimal radiographic abnormalities.
CONCLUSION: In patients with suspected diffuse lung disease, obtaining high-resolution CT scans with the patient prone may be useful when chest radiographs show normal findings, possibly abnormal findings, or minimal abnormalities indicative of diffuse lung disease. However, such scans are of little value in patients whose radiographs show abnormalities indicative of diffuse lung disease.