Calcification is a metamorphic lesion in pathology. Fatty acid decomposition in the damaged tissue causes local pH changes, and calcium ions are deposited in the form of calcium phosphate or calcium carbonate, generally in degenerative lesions or necrotic tissues. Calcification is more common in the healing stage of caseous tuberculosis lesions in the lungs or lymph nodes, and may also occur in certain lung tumor tissues or cyst walls. In addition to pulmonary tuberculosis, multiple calcifications in both lungs can also be seen in silicosis, intrapulmonary metastasis of osteosarcoma, pulmonary histoplasmosis, and alveolar microlithiasis.
X-ray
On the chest plain film, calcification is manifested by hyperdense, sharply marginated, differently sized, punctate or massive or spherical, localized or diffuse lesions. Calcification in pulmonary tuberculosis or lymph node tuberculosis present single or multiple spots. Silicosis calcification is often manifested by scattered, multiple nodules or annular dense opacities in both lungs. Eggshell calcification is common in lymph nodes.
CT
On the mediastinal window, calcification is significantly higher than soft tissue in density, with a CT value of more than 100HU. Laminated and annular calcifications often suggest benign lesions, mostly in granulomas or tuberculous lesions. Popcorn calcification can be seen in typical pulmonary hamartoma. Few peripheral lung cancers may also have calcifications, which are solitary punctate or localized multiple granular. Eggshell calcifications in hilar lymph nodes are common in pneumoconiosis. Generally, calcification in the lesion is directly proportional to the possibility of benignity. Small, diffuse, nodular calcifications are more common in alveolar microlithiasis and silicosis.
Figure 1 Calcified lesions
a, b. HRCT shows a. annular calcification (↗) in tuberculoma; b. calcified satellite lesion (↗) in tuberculoma; c. popcorn calcification (↗) in pulmonary hamartoma; d. multiple granular calcifications (↗) in peripheral lung cancer.
MRI
MRI is far less sensitive and accurate than CT in visualization of calcification. Most small calcified lesions in the lungs cannot be visible, large calcified lesions can be hypointense in the lung lesions, and completely calcified lesions cannot be visible.