Biopsy-proved idiopathic pulmonary fibrosis: spectrum of nondiagnostic thin-section CT diagnoses.

Purpose: To document the spectrum of misleading thin-section computed tomographic (CT) diagnoses in patients with biopsy-proved idiopathic pulmonary fibrosis (IPF). Materials and Methods: This study had institutional review board approval, and patient consent was not required. Three observers, blinded to any clinical information and the purpose of the study, recorded thin-section CT differential diagnoses and assigned a percentage likelihood to each for a group of 123 patients (79 men, 44 women; age range, 27-82 years) with various chronic interstitial lung diseases, including a core group of 55 biopsy-proved cases of IPF. Patients with IPF in the core group, in whom IPF was diagnosed as low-grade probability (<30\%) by at least two observers, were considered to have atypical IPF cases, and the alternative diagnoses were analyzed further. Results: Thirty-four (62\%) of 55 biopsy-proved IPF cases were regarded as alternative diagnoses. In these atypical IPF cases, the first-choice diagnoses, expressed with high degree of probability, were nonspecific interstitial pneumonia (NSIP; 18 [53\%] of 34), chronic hypersensitivity pneumonitis (HP; four [12\%] of 34), sarcoidosis (three [9\%] of 34), and organizing pneumonia (one [3\%] of 34); in eight (23\%) of 34 cases, no single diagnosis was favored by more than one observer. Frequent differential diagnoses, although not always the first-choice diagnosis, were NSIP (n = 29), chronic HP (n = 23), and sarcoidosis (n = 9). Conclusion: In the correct clinical setting, a diagnosis of IPF is not excluded by thin-section CT appearances more suggestive of NSIP, chronic HP, or sarcoidosis. (c) RSNA, 2010.