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Prior imaging studies should always be reviewed whenever they are available to determine possible growth or stability (grade 1A; strong recommendation, high-quality evidence). Comparisons should include the earliest available study and more recent studies. Note that differences in scanning technique, such as use of thick sections for previous imaging, may make comparison less accurate, especially for small nodules; therefore, routine use of contiguous thin-section reconstruction and archiving is important (20). Recommendations for Solid Lung NodulesRecommendation 1: single solid noncalcified nodules.—Solid nodules smaller than 6 mm (those 5 mm or smaller) do not require routine follow-up in patients at low risk (grade 1C; strong recommendation, low- or very-low-quality evidence). There is a paucity of direct evidence regarding cancer probability in small nodules in low-clinical-risk situations. However, there is abundant evidence for cancer risk in current smokers or those who recently quit smoking and who have been studied in the context of lung cancer screening programs. The risk of cancer in patients who have never smoked and in younger patients is known to be significantly lower, with a relative risk on the order of 0.15 in the United States when compared with risk in heavy smokers in the case of solid nodules (21). Given that the average risk of cancer in solid nodules smaller than 6 mm in patients at high risk is less than 1%, it is reasonable to assume an even lower risk in a patient with low clinical risk (7,22). This recommendation is consistent with our policy of excluding nodules with a less than 1% risk of cancer from routine CT follow-up. Solid nodules smaller than 6 mm do not require routine follow-up in all patients with high clinical risk; however, some nodules smaller than 6 mm with suspicious morphology, upper lobe location, or both may warrant follow-up at 12 months (grade 2A; weak recommendation, high-quality evidence.). These revised guidelines increase the size threshold for routine follow-up of solid nodules to 6 mm. This change is based on supporting data from several screening trials that indicate the risk of cancer in nodules smaller than 6 mm is considerably less than 1%, even in patients at high risk (6,7). On the other hand, suspicious morphology, upper lobe location, or both can increase cancer risk into the 1%–5% range; therefore, follow-up at 12 months may be considered, depending on comorbidity and patient preferences. Earlier follow-up is not recommended in such instances, as experience has shown that such small nodules, if malignant, rarely advance in stage over 12 months, whereas a short-term follow-up examination showing no apparent change may provide false reassurance. An exception may be made in some patients with technically suboptimal initial scanning results to obtain a high-quality baseline study for future comparison or in nervous patients who may be reassured by evidence of short-term stability. Solitary noncalcified solid nodules measuring 6–8 mm in patients with low clinical risk are recommended to undergo initial follow-up at 6–12 months depending on size, morphology, and patient preference (grade 1C: strong recommendation, low- or very-low-quality evidence). One follow-up examination should suffice in many instances. If morphology is suspicious or if stability is uncertain, an additional study may be obtained after a further 6–12 months. The risk of malignancy is very low in this category, and not all solid nodules require traditional 2-year follow-up. The recommendation for 2-year follow-up was based on earlier studies with thick CT sections or chest radiographs and was made before the important differences between solid and subsolid nodules were recognized (6,7). Although some solid cancers have been reported to grow very slowly, with doubling times of more than 700 days and failure to clearly demonstrate growth for up to 2 years, these reports were also based on analysis of thicker-section CT images and evaluation on hard-copy images (23 |