). In most instances, metastases will grow perceptibly within 3 months. An analysis of subjects with multiple nodules in the NELSON trial showed an increase in risk for primary cancer, as the total nodule count increased from 1 to 4, but a decrease in risk for those with five or more nodules, most of which likely resulted from prior granulomatous infection (29).
 Figure 8: CT image shows multiple solid nodules of varying size with lower zone predominance (arrows) secondary to metastatic thyroid carcinoma. The dominant nodule should be used as a guide to management; however, additional nodules should also be monitored on follow-up images. In this context, the term dominant refers to the most suspicious nodule, which may not be the largest. Solitary Subsolid Lung NodulesRecommendation 3: solitary pure ground-glass nodules.—For pure ground-glass nodules smaller than 6 mm (ie, 5 mm and smaller) in diameter, no routine follow-up is recommended (grade 1B; strong recommendation, moderate-quality evidence). Because of the high prevalence of ground-glass nodules smaller than 6 mm, we do not recommend follow-up scanning in every patient with such findings. However, this does not preclude follow-up in selected patients with subsolid nodules (including those with pure ground-glass or part-solid types) close to 6 mm in size with suspicious morphology or other risk factors. This item has been modified slightly from the previous recommendation, providing an option of 2- and 4-year follow-up in selected subjects at high risk. This reflects data from Asian populations, indicating that up to 10% of such nodules may grow and that nearly 1% may progress to adenocarcinoma over many years. However, the finding of malignant transformation in less than 1% of all patients is strong evidence for a conservative approach to the vast majority of these typically noninvasive lesions (30). For pure ground-glass nodules 6 mm or larger, follow-up scanning is recommended at 6–12 months and then every 2 years thereafter until 5 years (grade 1B; strong recommendation, moderate-quality evidence). The previous recommendation of initial follow-up at 3 months (2) has been changed to follow-up at 6–12 months because earlier follow-up is unlikely to affect the outcome of these characteristically indolent lesions. To date, numerous reports have shown that pure ground-glass nodules that are 6 mm or larger may be followed safely for 5 years, with an average of 3–4 years typically required to establish growth or, less commonly, to diagnose a developing invasive carcinoma (Figs 9, 10) (30–34). 
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