Abstract
Disseminated pulmonary ossification (DPO) is a rare disease characterised by diffuse calcification/ossification of lung parenchyma. Most of the cases are idiopathic, while rest of the cause may have underlying cause like lung congestion, lung injury, lung amyloidosis and interstitial lung disease (ILD). We present a rare case of 58-year-old women with progressive dyspnoea and dry cough. On CT, there were extensive confluent nodular and linear calcification of bilateral lung parenchyma associated with lung fibrosis. Imaging findings lead to diagnosis of DPO associated with idiopathic lung fibrosis. Development of such calcification in ILD is very unusual, therefore knowledge of imaging features of DPO is very crucial for its diagnosis.
Case presentation
A 58-year-old female patient presented with progressively increasing shortness of breath and dry cough for one year. There was no history of fever, haemoptysis, and productive cough. There was no similar family history, no history of occupational exposure, smoking, or any chronic cardiac and renal disease. She had been previously treated for lower respiratory tract infection with antibiotics at peripheral hospitals without improving her symptoms. She brought with her a frontal chest radiograph, done five months before, which revealed diffusely scattered reticular opacities in bilateral lung fields associated with dense calcifications predominately in bilateral lower zones. Her electrocardiogram and routine blood examination were within normal limits. Pulmonary function test revealed a restrictive pattern with reduced total lung volume and diffusion capacity.
A High-resolution CT of the thorax was ordered, which revealed (Figs 1 and 2). diffuse coarse reticulations with interlobular and intralobular septal thickening in bilateral lungs showing apicobasal gradient and peripheral predominance. A few tiny subpleural cystic areas were also seen in both upper lobes and the right lower lobe, representing early honeycombing. Ill-defined branching calcific densities were present in bilateral lung parenchyma along thickened interlobular septa and reticular opacities, having HU values in the range of 435–536. Confluent areas of alveolar calcification/ossification were also seen, more predominant in both lower lobes. The cardiothoracic ratio was mildly increased with dilated main pulmonary trunk (31 mm in diameter). Based on these CT findings, a diagnosis of disseminated pulmonary ossification (DPO) associated with fibrosing interstitial lung disease (usual interstitial pneumonia pattern) was made. Additionally, mild cardiomegaly with pulmonary arterial hypertension was likely secondary to interstitial lung disease. The patient declined to undergo lung biopsy and was kept on symptomatic and conservative treatment.
High-resolution computed tomography thorax images in axial (a, b) and coronal (c) planes demonstrate bilateral lung fibrosis (blue arrows) in the form of diffuse coarse reticulations and septal thickening in bilateral lungs showing apicobasal gradient and peripheral predominance. Early honeycombing is seen in right lung (white arrow)
Citation: Imaging 14, 1; 10.1556/1647.2022.00072
High-resolution computed tomography thorax images in axial (a, b) and coronal (c) planes demonstrate bilateral lung fibrosis (blue arrows) in the form of diffuse coarse reticulations and septal thickening in bilateral lungs showing apicobasal gradient and peripheral predominance. Early honeycombing is seen in right lung (white arrow)
Citation: Imaging 14, 1; 10.1556/1647.2022.00072
High-resolution computed tomography thorax images in axial (a, b) and coronal (c) planes demonstrate bilateral lung fibrosis (blue arrows) in the form of diffuse coarse reticulations and septal thickening in bilateral lungs showing apicobasal gradient and peripheral predominance. Early honeycombing is seen in right lung (white arrow)
Citation: Imaging 14, 1; 10.1556/1647.2022.00072
Non-contrast computed tomography thorax images in mediastinal window settings in axial (a, d) and coronal (b) planes, and bone window settings in axial (c) plane demonstrates confluent linear and nodular calcification/ossification (blue arrows) in bilateral lungs more predominant in bilateral lower lobes and areas of fibrosis. Associated mild prominence of main pulmonary artery seen (white arrow in d)
Citation: Imaging 14, 1; 10.1556/1647.2022.00072
Non-contrast computed tomography thorax images in mediastinal window settings in axial (a, d) and coronal (b) planes, and bone window settings in axial (c) plane demonstrates confluent linear and nodular calcification/ossification (blue arrows) in bilateral lungs more predominant in bilateral lower lobes and areas of fibrosis. Associated mild prominence of main pulmonary artery seen (white arrow in d)
Citation: Imaging 14, 1; 10.1556/1647.2022.00072
Non-contrast computed tomography thorax images in mediastinal window settings in axial (a, d) and coronal (b) planes, and bone window settings in axial (c) plane demonstrates confluent linear and nodular calcification/ossification (blue arrows) in bilateral lungs more predominant in bilateral lower lobes and areas of fibrosis. Associated mild prominence of main pulmonary artery seen (white arrow in d)
Citation: Imaging 14, 1; 10.1556/1647.2022.00072
Disseminated pulmonary ossification (DPO) is a rare condition characterized by progressive new bone formation with or without marrow elements involving alveolar and/or interstitial spaces of lung parenchyma. [1] Imaging features of this entity are still not well described in the literature, with most of the reported cases being identified either on histopathological evaluation or autopsy. [2] DPO can be idiopathic or secondary. The secondary form of DPO is more common where an underlying cause of ossification is present. [3] DPO has been reported in those with pre-existing lung disease, particularly lung congestion secondary to mitral stenosis, following severe lung injury, pulmonary amyloidosis, and in association with fibrosing interstitial lung disease (ILD). [3] Two forms of DPO are described; one is nodular form, and the other is dendriform. [3] Nodular form is more common, characterized by 1–5 mm small calcified nodules deposited in alveolar spaces, and is often associated with pulmonary congestion secondary to mitral valve disease. Dendriform type is less common, characterized by ossification along alveolar interstitium and septa, which on imaging appears as branching calcification along alveolar septa and pre-existing areas of fibrosis. [4] This form is associated with fibrosing ILD and chronic inflammation.
The pathophysiology of DPO development in fibrosing ILD is still not well understood but thought to be osseous metaplasia secondary to chronic insult. [3] In a study by Egashira et al., they found the prevalence of DPO in fibrosing ILD was between 11.9 and 18.6%. [5] The prevalence of DPO was higher in idiopathic pulmonary fibrosis (IPF) than other forms of ILD. [5] Moreover, identification of DPO on CT is an independent predictor for IPF diagnosis. [5] Changes of DPO are more predominant in areas affected with fibrosis and thus often show lower lobe predominance. Kim et al. and Egashira et al. reported that the dendriform type of DPO described on histopathology does not always represent the branching pattern of ossification on CT and the nodular appearance of DPO on CT shows both dendriform and nodular pattern of ossification on histopathological evaluation. [5, 6] In our case, widespread confluent nodular and branching ossifications were seen, predominantly overlapping the areas of fibrosis, which is consistent with the appearance described in a few previous studies. [5, 6] Treatment of DPO is based on the control of the underlying disease.
The differential diagnosis of DPO on imaging is dystrophic calcification, metastatic calcification, and pulmonary alveolar microlithiasis (PAM). [7] In dystrophic calcification, clinical and radiological evidence of previous infection or dust exposure will be present; moreover, calcification is less diffuse and more prominent in size. Metastatic calcifications are seen in patients with chronic renal disease, chronic dialysis, hyperparathyroidism, and orthotopic liver transplantation. In PAM, family history is usually positive, and CT shows numerous sand-like calcifications with the subpleural and peri-bronchial distribution.
Conflicts of interest
There is no conflict of interest.
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Contribution
All authors contributed equally to the final form of manuscript.
Acknowledgement
None.
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