Figure 20.

A-D, Histologic findings of an organizing pneumonia (OP) pattern (OPP). In this case of cryptogenic OP with multifocal lung involvement, a low-power histologic image (A) shows patchy areas of polypoid intraluminal plugs (thick arrows) of loose connective tissue that protrude into distal airways. The adjacent lung parenchyma is relatively normal (thin arrows). B, In this field, the polypoid plugs are seen within alveolar spaces and alveolar ducts (thick arrows), but bronchiolar involvement is minimal (thin arrows). The connective tissue is the same age, and the alveolar architecture is preserved. C, In this case of focal OP, there is a nodular lesion consisting of the OPP as seen in (A) and (B) surrounded by relatively normal lung (thin arrows). D, The lesion consists of polypoid plugs of loose connective tissue within distal airspaces (thick arrows).