Cicatricial Organizing Pneumonia Mimicking a Fibrosing Interstitial Pneumonia

Abstract

Aims

Organizing pneumonia (OP) is composed of loose granulation tissue plugs in distal airspaces; these disappear with steroid treatment. Recently a variant labeled "cicatricial" OP has been described in which the granulation tissue organized to much denser fibrous tissue but still retained the usual pattern of OP. Here we report 10 patients thought to have an interstitial lung disease, and who on biopsy had a variant of cicatricial OP characterized by linear bands or small nodular masses of dense fibrous tissue that does not resemble ordinary OP.

Methods and Results

The bands/nodules were usually randomly distributed but occasionally resembled fibrotic nonspecific interstitial pneumonia in local areas. Small foci of loose granulation tissue at the edge of the fibrotic bands sometimes mimicked fibroblast foci. Recognizable conventional OP was always present, but often in very small amounts. Four cases, including one patient with Ehlers Danlos syndrome, showed formation of bone in the fibrotic bands and nodules. On CT scan of the chest some cases looked like typical OP, but some demonstrated only irregularly distributed linear opacities, sometimes with associated calcification. Follow-up imaging on 6 cases showed that the process either markedly improved or remained stable over time; no case had progressive disease.

Conclusions

Cicatricial OP with this pathologic pattern represents an uncommon form of OP that appears to be a generally benign process which may have persisting linear opacities on CT scan but that does not progress; however, it can be confused on biopsy and CT with a fibrosing interstitial pneumonia.

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