[PIRADS}: A small lump, swelling or collection of tissue. [Fleischner Society]: The chest radiographic appearance of a nodule is a rounded opacity, well or poorly defined, measuring up to 3 cm in diameter. (a) Acinar nodules are round or ovoid poorly defined pulmonary opacities approximately 5–8 mm in diameter, presumed to represent an anatomic acinus rendered opaque by consolidation. This classification is used only in the presence of numerous such opacities. (b) A pseudonodule mimics a pulmonary nodule; it represents, for example, a rib fracture, a skin lesion, a device on the surface of the patient, anatomic variants, or composite areas of increased opacity