PurposeTo investigate the predictive clinical and imaging factors associated with pulmonary metastasis in pulmonary nodules (PNs) ≤10 mm in patients with primary extrapulmonary malignancy (PEPM) on initial CT as well as the inter-nodular imaging features in the non-solitary PNs patients, to make a more reliable diagnosis and appropriate management of the PNs at an earlier stage after detection.Materials and methods161 patients with PNs ≤10 mm were reviewed from April 2013 to December 2013. The nature of PNs were determined on the interval change in imaging features on serial CT images (158 patients) and histologically proven (three patients). Independent predictors of changed PNs on initial CT were examined by multivariate regression analysis.Results36.6% of patients developed interval change in nodules size. The average interval of the first change was 65.0 days (29–144 days). Tumor staging of III (P = 0.011) and IV (P < 0.001), the nodules number of 2–4 (P = 0.016), 5–9 (P < 0.001) and 10–20 (P < 0.001), the nodules margin of being smooth (P = 0.001) and slight lobulated (P < 0.001), and nodules with no near short strips (P = 0.001) were significant predictors of changed PNs. For patients with non-solitary PNs, 40.2% had PNs with identical imaging features, the incidence rate of change of which (74.3%) was significantly higher compared with that of varied features (32.7%), P < 0.001; and 94.3% of patients had all nodules per patient showing consistent prognosis.ConclusionsFor PNs ≤10 mm in patients with PEPM on baseline CT, the morphological characteristics and primary malignancies stage could differentiate the majority of the PNs. The interval for further CT evaluation of uncertain PNs should be early at 1–3 months after detection, and increased alert is needed for the possibility of pulmonary metastasis when an early interval change was detected.