Metastatic pulmonary calcification (MPC) is a form of pulmonary calcification where there is calcium deposition in normal lung parenchyma. It is most commonly due to chronic renal failure.
Metastatic pulmonary calcification is an unfortunate term in that "metastatic" suggests a malignant process, but in fact purely refers to the spread to, and deposition in, the lungs, of the excess calcium. In truth, malignancy is only very rarely the etiology.
The calcification refers to a cellular pathological process, and it is not unusual to see no calcification on imaging at all.
The majority of patients are asymptomatic. In a small minority dyspnea and a chronic dry cough are seen. Rarely, severe respiratory failure and death may result 13.
It is one of two types of tissue calcification and occurs when calcium is deposited in previously normal tissue, in contrast to dystrophic calcification that occurs in previously damaged tissue 12.
It can occur in a variety of benign and malignant disorders such as:
- chronic renal failure: considered the commonest cause 5
- primary and secondary hyperparathyroidism
- vitamin D intoxication
- intravenous calcium therapy
- milk-alkali syndrome
- multiple myeloma
- massive osteolysis caused by metastases
Metastatic pulmonary calcification is typically most marked in the upper lobes. This is thought to be due to a higher ventilation-to-perfusion ratio in the apices, hence less CO2 pressure and a more alkaline environment.
The plain chest radiograph is typically normal due to its inherent insensitivity in detecting the often small quantities of calcium present. Indeed the most common pattern - if any abnormality is present at all - is non-specific air space consolidation, mimicking pulmonary edema or pneumonia.
Several CT patterns have been described.
It is usually characterized by centrilobular fluffy ground-glass nodular opacities that may or may not appear calcified. Very rarely, ring-like calcification may be seen 5.
Other less common patterns include 11:
- consolidation with high attenuation
- small dense nodules
- peripheral reticular opacities associated with small calcified nodules
- ground-glass opacities without centrilobular ground-glass nodular opacity
Rarely, the following may also be present:
- vascular calcification within the chest wall
- pleural effusion
Increased uptake in pulmonary opacities is confirmatory, and may precede any apparent findings on the plain chest radiography.
Treatment and prognosis
Overall prognosis will depend on the underlying cause.
The condition may be reversible, and a resolution of the radiological findings, and also symptoms, has been reported, following curative parathyroidectomy, renal transplant, or definitive dialysis 13.
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