CT features of focal organizing pneumonia: an analysis of consecutive histopathologically confirmed 45 cases

To study the CT characteristics of solitary focal organizing pneumonia (FOP).

Chest CT of consecutive 45 patients (34 males and 11 females, median age: 56 years) with confirmed FOP were analyzed. The CT features between large FOP (>3 cm, n=27) and small FOP (≤ 3 cm, n=18) were compared.

FOP lesions predominately located in peripheral lungs (86.7%), with the right lower lobe being most common lobe (44.4%). No lesion mainly located in the inner 1/3 of lungs. All large lesions were polygon in shape and had an irregular margin, while small lesions were more likely to be round or oval with an irregular or smooth border. Air bronchogram or small bubble-like lucency was present in majority of the lesions. 42.2% of lesions had incompact internal structure with inhomogeneous density besides air component. Most lesions were associated with a contraction or convergence of surrounding vessels; while no pulmonary vessel was interrupted abruptly by a small FOP lesion. Majority of large lesions had broad contact with the pleura, while only one patient had mild pleural effusion. Mild mediastinal lymph nodes enlargement was present in about 1/5 of the patients.

Compared with the known CT features of lung cancer, our results suggest differential diagnosis can often be made for large FOP, while small FOP may resemble lung cancer.