Jones J, Silverstone L, Knipe H, et al. Pulmonary nodule. Reference article, Radiopaedia.org (Accessed on 03 Oct 2024) https://doi.org/10.53347/rID-10187
Pulmonary nodules are small, rounded opacities within the pulmonary interstitium. Pulmonary nodules are common and, as the spatial resolution of CT scanners has increased, detection of smaller and smaller nodules has occurred, which are more often an incidental finding.
They are generally homogeneous (without air bronchograms or alveolograms) and are well-defined since their margins are sharp and they are surrounded by normally aerated lung parenchyma. They are quite separate from airspace nodules that often have an irregular margin and are usually ~8 mm in diameter. (For further discussion, see the article on nodular opacification.)
Always be aware of artifacts, especially on radiographs, where buttons or nipple shadows can often be mistaken for a true pulmonary nodule 7.
Practical points
The term micronodule has been defined variably by different position statements. In the National Lung Screening Trial (NLST) all nodules with <4 mm maximum diameter were recorded as micronodules 8. Some authors consider lesions measuring <3 mm as micronodules 9. In this article, we follow the cutoff recommended by the Fleischner Glossary published in 2024 which classifies nodules <6 mm as micronodules, which are generally ‘non-actionable’ 11.
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