A 67-year-old man with no significant medical history presents for evaluation of incidental findings on a chest CT scan (Figure 1). He emigrated from Malaysia where he worked as a pipe fitter and boilermaker for more than 30 years. He has no symptoms, with normal vital signs and unremarkable physical examination results. Pulmonary function tests reveal mild diffusion impairment without obstruction or restriction. Basic laboratory analysis results as well as angiotensin-converting enzyme levels were within normal limits.

Bronchoscopy with bronchoalveolar lavage (BAL) and cryobiopsy is performed. Histopathologic analysis of the lung biopsy specimen shows an increased number of histiocytes in alveolar spaces and interstitium with minimal fibrosis and preserved alveolar architecture (Figure 2). Positive Prussian blue histochemical staining of the BAL and lung biopsy specimens help to confirm the diagnosis (Figure 3).

Figure 1. Noncontrast-enhanced chest CT scans lung windows (A-C, axial views; D, coronal view).

Figure 2. Lung biopsy specimen. Hematoxylin-eosin stain (×100 magnification).

Figure 3. Prussian blue stain. A, Alveolar lavage fluid (×1,000 magnification). B, Cryobiopsy specimen (×100 magnification).