Chest Imaging

Micronodule

discrete, small, round focal nodular opacity no more than 7 mm in diameter. On chest radiographs, the presence of multiple micronodules results in a miliary pattern or nodular pattern. Micronodules can be seen on HRCT in a number of diffuse lung diseases, and can reflect the presence of either interstitial or air-space abnormalities (Fig.1).

Micronodules are commonly seen in sarcoidosis, metastatic carcinoma, silicosis and coal workers pneumoconiosis, miliary tuberculosis or pulmonary fungal infection, endobronchial spread of infection or neoplasm, airway diseases such as bronchiectasis or cellular bronchiolitis, hypersensitivity pneumonitis, and histiocytosis X pulmonary. Micronodules can be classified on HRCT according to their distribution (e.g. perilymphatic, centrilobular or at random). These classifications can be valuable in differential diagnosis.

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Fig.1

HRCT showing small discrete nodules in a patient with metastatic breast cancer.
Micronodule, Fig.1