Fig. 3

Pathological examination

a): Right lower lobectomy was performed

The cut surface revealed a yellow tan-colored nodule approximately 15 mm in size

b): Nodules approximately 15 mm in size are seen with dilation of the bronchioles

(original magnification ×1, hematoxylin and eosin staining)

c): Around the margin of the nodule, many hyalinized fibrotic plugs were observed inside the alveolar space. They were interpreted as cicatricial variants of organizing pneumonia

(original magnification ×40, hematoxylin and eosin staining)

d): Higher magnification revealed plasmacytic infiltration around the dilatated bronchiole

(original magnification ×400, hematoxylin and eosin staining)

e): Deposition of collagenous fiber in Masson type polyp is a characteristic feature of cicatricial variant of organizing pneumonia

(original magnification ×400, hematoxylin and eosin staining)

f): Immunohistochemistry of Treponema pallidum revealed spiral fungi in the necrotic debris of dilated bronchioles