Non-malignant metastatic pulmonary calcification

CT findings

of high-attenuation pulmonary abnormalities. Metastatic pulmonary calcification in a 24-year-old man who had known chronic renal failure. Axial CT at a mediastinal and b parenchymal windows demonstrates bilateral centrilobular fluffy ground-glass nodular opacities that contain foci of calcification (arrows)

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Metabolic and

storage lung diseases: spectrum of imaging appearances. A 65-year-old woman with metastatic calcification from chronic kidney failure. a AP radiograph shows dense foci of consolidation (arrows) in the lower lungs. b, c Unenhanced CT images show mass-like foci of calcified lung (arrows)

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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.

Terminology

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 of the excess calcium in the lungs. 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.

Clinical presentation

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 .

Pathology

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 .

Causes

It can occur in a variety of benign and malignant disorders such as:

chronic renal failure: considered the commonest cause
primary and secondary hyperparathyroidism
sarcoidosis
vitamin D intoxication
intravenous calcium therapy
milk-alkali syndrome
multiple myeloma
massive osteolysis caused by metastases

Distribution

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.

Radiographic features

Plain radiograph

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.

CT

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 .

Other less common patterns include :

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

Nuclear medicine

Bone scan

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 .