Pulmonary Calcification and Ossification: Pathogenesis, CT Appearance, and Specific Disorders

Pulmonary high attenuation may be caused by calcification or ossification, both of which are common phenomena with distinct pathogeneses, histologies, and radiologic appearances. Pulmonary calcification is divided into metastatic pulmonary calcification (MPC), caused by systemic hypercalcemia, and dystrophic pulmonary calcification (DPC), caused by local lung injury. MPC often demonstrates diffuse calcified nodules, which can be subtle and amorphous on CT images, with associated sandlike, fine ground-glass, or consolidative opacities. Conversely, DPC often appears nodular and is localized to areas of lung injury and thus is associated with other signs of lung damage, such as prior infection, fibrosis, or scarring. In contrast to calcification, pulmonary ossification is not a consequence of a localized or systemic metabolic abnormality but instead is found in the setting of chronic lung disease, which induces fibroblast-to-osteoblast transformation and bone deposition. Pulmonary ossification can be divided into nodular (NPO) and dendriform (DPO) patterns. NPO often appears as multiple small well-defined round nodules that are uniform in size and appearance. NPO classically is seen with chronic venous congestion in a subpleural predominant distribution and increasingly is recognized in pathologic findings in the setting of fibrosing interstitial lung disease (ILD). DPO appears more commonly as peripheral irregular branching opacities and can be seen with ILD. Additionally, pulmonary calcification or ossification can occur in association with protein deposition disease, including pulmonary amyloidosis, or in benign neoplasms or metastatic malignancies. Pulmonary alveolar microlithiasis is a distinct entity relating to phosphate metabolism. Pulmonary calcification and ossification can provide insight into patients' underlying disease processes and clinical context for radiologic study interpretation. ^©RSNA, 2025 Supplemental material is available for this article.