Figure 9. .

Schematic representation of micronodules distribution patterns. (a) Typical perilymphatic distribution involving the parahilar peribronchovascular interstitium until terminal bronchioles, the subpleural area, along the fissures or interlobular septa. A typical perilymphatic distribution is seen in sarcoidosis, lymphangitic carcinomatosis or silicosis. (b) In case of random distribution, the distribution is uniform without respect of anatomic structures. This suggests a hematogenous spread of disease, particularly miliary metastases, tuberculosis, fungal or viral infection. (c) Centrilobular distribution is characterized by the presence of multiple small nodules often ill-defined grouped within the center of the secondary pulmonary lobule, with a location at least 3 mm away from the pleura. Therefore, the key point for the recognition of this pattern is the absence of any nodule along the pleural interface. This distribution is primarily suggestive of bronchial and peribronchial disease, but may also be related to vascular or perivascular disease, and more rarely interstitial disease predominating around the centrilobular bronchiole and artery.