Accelerated Pulmonary Ossification as a Sequela of SARS-CoV-2 Pneumonia.

This case illustrates extensive dendriform lung ossification manifesting after SARS-CoV-2 pneumonia. Organizing pneumonia is an established CT finding in subacute SARS-CoV-2 infection (1,2), usually manifesting as bilateral consolidations (80%–95% of the cases) in a predominantly peripheral or peribronchial distribution, sometimes sparing the subpleural regions (3). Histologic analysis reveals plugs of fibroblastic tissue filling bronchioles and airspaces (3,4), which usually disappear after steroid treatment. However, fibromyxoid tissue may progress to fibrosis, a condition recently described as “cicatricial organizing pneumonia (4–6).” Some of these cases may evolve with pathologic osseous metaplasia, seen on imaging as nodular and branching calcifications, described as dendriform pulmonary ossification (5). This finding is usually seen in patients with underlying lung fibrosis, most commonly in usual interstitial pneumonia, and it is considered as a marker of chronicity and severity of lung fibrosis (7).

Differential diagnoses include dystrophic calcifications, metastatic calcifications, and pulmonary alveolar microlithiasis. Dystrophic calcifications occur in diseased lung, in the settings of granulomatous infections, sarcoidosis, occupational lung diseases, and metabolic diseases (eg, as amyloidosis). Metastatic calcifications occur in normal lung due to hypercalcemia secondary to end-stage kidney disease. The differential diagnosis also includes nodular ossification seen in patients with chronic venous lung congestion (8). Normal renal function, phosphate calcium homeostasis, and the absence of any relevant past medical history or concomitant diseases excluded other causes of lung calcification/ossification in this case (Figs 1, 2).

Figure 1:

Images in a 49-year-old man who presented to the emergency department with SARS-CoV2 infection. A and B, Non–contrast-enhanced chest CT scans obtained 1 month after the onset of symptoms show multifocal peribronchovascular and peripheral consolidation, relatively sparing the subpleural region, consistent with organizing pneumonia. Follow-up chest CT was performed 6 months after steroid treatment. C, Axial and, D, coronal CT images show multiple micronodular calcifications within faint ground-glass opacities.

Figure 2:

Bone window images in same patient. Comparison between A, initial and, B, follow-up CT on axial maximum intensity projection images shows interval development of micronodular and branching calcifications, confirmed on C, coronal and, D, magnified axial views. Follow-up lung function testing revealed decreased diffusion capacity.