Mosaic Attenuation

The mosaic pattern of lung attenuation refers to a patchwork of regions of differing attenuation. The term is descriptive and nonspecific. It can be seen with:

• Small-airways disease (shown above): Air trapping and bronchial dilatation commonly seen. Areas of increased attenuation have relatively large vessels, while areas of decreased attenuation have small vessels. Causes include:
  • Bronchiolitis obliterans: Idiopathic or due to collagen vascular disease (e.g., rheumatoid arthritis), toxic gas inhalation, pneumonia (viral or bacterial), graft versus host disease, and drugs.
  • Asthma
• Occlusive vascular disease: Also known as mosaic oligemia and mosaic perfusion. Presence of air trapping and bronchial dilatation make it hard to differentiate this entity from small airways disease. Areas of increased attenuation have relatively large vessels, while areas of decreased attenuation have small vessels. Causes include:
  • Chronic pulmonary thromboembolism
  • Pulmonary venooclusive disease
  • Pulmonary arterial hypertension
  • Polyarteritis nodosa
• Patchy interstitial disease: The areas of increased attenuation are abnormal. The size of vessels within these areas of ground-glass attenuation is usually similar to that of uninvolved lung, allowing differentiation from occlusive vascular disease and small-airways disease. May have air trapping, especially in patients with hypersensitivity pneumonitis. Causes include:
  • Hypersensitivity pneumonitis
  • Desquamative interstitial pneumonitis
  • Alveolar proteinosis
  • Cryptogenic organizing pneumonia
  • Bronchoalveolar carcinoma
  • Nonspecific interstitial pneumonitis
  • Lymphangitic carcinomatosis
  • Sarcoidosis
  • Pulmonary edema
  • Acute interstitial pneumonitis

References

• Hansell DM, Bankier AA, MacMahon H, McLoud TC, Müller NL, Remy J. Fleischner Society: glossary of terms for thoracic imaging. Radiology. 2008 Mar;246(3):697-722.
• Worthy SA, Müller NL, Hartman TE, Swensen SJ, Padley SP, Hansell DM. Mosaic attenuation pattern on thin-section CT scans of the lung: differentiation among infiltrative lung, airway, and vascular diseases as a cause. Radiology. 1997 Nov;205(2):465-70.