Correct!
Answer: 3. Metastatic pulmonary calcification.
The persistence of the opacities unchanged for more than 10 years strongly argues against either an active infection or post-transplant lymphoproliferative disorder. Furthermore, the presence of calcification would also be highly unusual for either of these two conditions. While hydrostatic pulmonary edema may produce ground-glass attenuation centrilobular nodules, and a small right pleural effusion is present on the thoracic CT, hydrostatic edema would not preferentially occur in the lung apices in most patients, nor should hydrostatic edema show calcification, nor would it persist on chest radiograph for 10 years. While subacute hypersensitivity pneumonitis classically produces ground-glass opacity centrilobular nodules, the thoracic CT findings in this disorder are typically more diffuse, as opposed to so heavily concentrated in the apices, and the nodules in patients with hypersensitivity pneumonitis typically do not calcify. Finally, the development of hypersensitivity pneumonitis would be unlikely in an immunosuppressed patient.
Discussion
Metastatic pulmonary calcification typically occurs in conditions that result in an elevated calcium-phosphate product, which favors deposition of calcium salts within the walls of alveoli and vessels within otherwise normal lungs. Parathyroid hormone excess may also play a role in “sensitizing” tissues for later calcium deposition. The most common condition to produce metastatic pulmonary calcification is chronic renal insufficiency, often in patients on hemodialysis. Other conditions that produce this disorder include hyperparathyroidism, hypervitaminosis D, and milk-alkali syndrome. The relatively alkaline environment in the pulmonary apices, due to a lower concentration of carbon dioxide, favors the deposition of calcium salts in this region of lung.
In contrast to metastatic pulmonary calcification, in which calcium deposition occurs in normal lung parenchyma, dystrophic pulmonary calcification occurs in areas of abnormal lung, typically in the presence of a normal calcium-phosphate product, usually at sites of prior parenchymal insults such as infection (tuberculosis, fungal, and viral infections), amyloidosis, and pneumoconioses.
Metastatic pulmonary calcification typically appears as upper lobe predominant poorly defined opacities that resemble nodules, masses, or consolidation on chest radiography. The nature of the abnormality is rarely recognized at chest radiography. Thoracic CT will show calcification within the opacities, and will also show that many of the opacities consist of centrilobular nodules that may, or may not, show calcium. Often these nodules show ground-glass attenuation. Often heavy bronchial wall and vascular calcification may be evident in patients with metastatic pulmonary calcification due to renal insufficiency. 99m Technetium methylene diphosphonate (MDP) bone scanning may show tracer uptake within the areas of pulmonary calcification.
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