Pulmonary Micronodules

A micronodule is a rounded opacity that measures < 3 mm in diameter at CT. Nodules can be located within the lung interstitium, the airspace or both. The differential diagnosis of diseases manifesting with interstitial micronodules varies widely, and affected patients have variable clinical presentations. Familiarity with the anatomy of the pulmonary interstitium is fundamental when assessing micronodules as a concentration of micronodules within a particular compartment may be the imaging clue to the correct diagnosis. Thin-section CT and HRCT are optimal for detection and characterization of pulmonary micronodules; once micronodules are identified, their distribution within the pulmonary interstitium must be determined according to their location with respect to the secondary pulmonary lobule, and characterized as centrilobular, perilymphatic or random.