Idiopathic Pulmonary Fibrosis: Spectrum of HRCT Appearances of Diagnostically Misleading Cases.

Purpose of the Study: To document the spectrum of misleading HRCT diagnoses in patients with biopsy-proven idiopathic pulmonary fibrosis (IPF). Methods: Three observers, blinded to any information, recorded HRCT differential diagnoses and assigned a percentage likelihood to each for a group of 123 patients (79 men, 44 women, age range 27 to 82; mean 59.8±9.5) with various chronic interstitial lung diseases, including a core study group of 55 biopsy-proven cases of IPF. Patients with IPF in the core study group in whom at least two out of three observers recorded the diagnosis of IPF as low grade probability (<30%) were considered ‘‘atypical IPF’’ cases, and the alternative diagnoses were further analyzed. Results: In 34 cases with atypical IPF on HRCT, the first choice diagnoses, expressed with high degree of probability, were nonspecific interstitial pneumonia (NSIP; n=18/34, 53%), chronic hypersensitivity pneumonitis (HP; n=4/34, 12%), sarcoidosis (n=3/34, 9%) and organizing pneumonia (OP; n=1/34, 3%); in 8/34 (23%) 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). Conclusions: In the correct clinical setting, a diagnosis of IPF is not excluded by HRCT appearances more suggestive of NSIP, chronic HP or sarcoidosis.