Pulmonary nodule

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.

Classification

Pulmonary nodules can be classified according to size, morphology and/or distribution.

Size

• miliary nodules: <2 mm
• pulmonary micronodule: 2-7 mm
• pulmonary nodule: 7-30 mm
• pulmonary mass: >30 mm

Morphology

• solid pulmonary nodules
  • calcified pulmonary nodules
• partly solid pulmonary nodules
• ground glass pulmonary nodules

Distribution

• perilymphatic pulmonary nodules
  • perifissural pulmonary nodules
  • subpleural pulmonary nodules
• centrilobular pulmonary nodules
• random pulmonary nodules

Radiographic features

They are generally homogeneous (without air bronchograms or alveolograms) and are well-defined since their margins are sharp and they are surrounded by normal aerated lung. 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.)

Differential diagnosis

The differential diagnosis for a nodule can be refined by its size, location, and density. Solitary pulmonary nodules and hyperdense pulmonary nodules are discussed further elsewhere.

A micronodular or miliary pattern is predominately seen in granulomatous processes, haematogenous pulmonary metastases, and pneumoconioses. Nodules and masses are most often seen in metastatic disease to the lung.

Always be aware of artifacts, especially on radiographs, where buttons or nipple shadows can often be mistaken for a true pulmonary nodule ⁷. 

See also

• pulmonary mass
• incidental lung nodules
  • British Thoracic Society guidelines for pulmonary nodules
  • Fleischner Society pulmonary nodule recommendations
  • Brock model
• necrobiotic lung nodules
• solitary pulmonary nodule