Small nodules detected on chest radiography: does size predict calcification?

STUDY OBJECTIVES: To determine whether the likelihood of lung nodule calcification can be predicted from nodule size as measured on a chest radiograph (CXR).

DESIGN: Retrospective review of CXRs of patients with lung nodules < or =1 cm in size detected on CT scanning. CT images were used to identify calcifications and to provide spatial localization for readers to visualize nodules on a CXR and to measure their size. A subset of these nodules then was reexamined by different readers who did not view the CT scans

SETTING: Two university hospitals (Albuquerque, NM; Dallas, TX) and a US Air Force/Veterans Administration medical center (Albuquerque, NM).

PATIENTS: Two hundred thirty-six nodules in 185 patients

RESULTS: One half of the nodules (118) seen on CT scans could not be located on CXR, of which 8 (7%) were calcified. The prevalence of calcifications in the other 118 nodules visualized on CXRs was much higher (71 of 118 nodules [60%]; p<0.005). Among the nodules visualized on CXRs, those < 7 mm in diameter (44 of 57 nodules [77%]) were more likely to be calcified than those > or = 7 mm in diameter (27 of 61 nodules [44%]; p<0.005). Radiographs of 42 of the smallest nodules visualized on CXRs by the initial readers later were examined prospectively by different readers who did not have access to the CT images. Thirty of 33 of the calcified nodules (91%) but only 3 of 9 of the noncalcified nodules (33%) were detected (p<0.005). These readers also recorded 40 additional small nodules that were not seen on CT scans, which were considered to be false-positives.

CONCLUSIONS: Nodules detected on CXRs that measure <7 mm in size are likely to be calcified or to represent a false-positive finding.