HRCT PATTERNS IN FIBROTIC INTERSTITIAL LUNG DISEASES: COMPARATIVE ANALYSIS OF IDIOPATHIC PULMONARY FIBROSIS, SARCOIDOSIS, HYPERSENSITIVITY PNEUMONITIS, AND CONNECTIVE TISSUE DISEASE–RELATED ILD

High-resolution computed tomography (HRCT) remains the cornerstone in the non-invasive evaluation of fibrotic interstitial lung diseases (ILDs), providing essential information for diagnostic classification and guiding clinical management. Despite well-established imaging criteria, many fibrotic ILDs share overlapping features that can complicate interpretation. This study aimed to evaluate and compare the HRCT patterns of idiopathic pulmonary fibrosis (IPF), sarcoidosis, fibrotic hypersensitivity pneumonitis (fHP), and connective tissue disease–associated ILD (CTD-ILD) in a single-center cohort, highlighting the distinguishing characteristics that aid in differential diagnosis. A total of 50 patients with multidisciplinary consensus diagnosis were retrospectively included: 15 with IPF, 12 with sarcoidosis, 13 with fHP, and 10 with CTD-ILD. All underwent volumetric inspiratory HRCT with collimation ≤1.5 mm. Image interpretation was performed by one experienced thoracic radiologist with over 10 years of subspecialty practice, who assessed the scans for zonal predominance, axial distribution, and fibrotic features including reticulation, honeycombing, traction bronchiectasis, ground-glass opacity, mosaic attenuation, and nodules. In the IPF group, fibrosis was predominantly basal and subpleural in 93% of cases, with honeycombing in 80% and traction bronchiectasis in 87%, while mosaic attenuation was rare. Sarcoidosis was characterized by upper- and mid-lung predominance in 75%, perilymphatic nodules in 83%, bronchial distortion in 58%, and less frequent honeycombing (25%). fHP showed diffuse or mid-lung fibrosis in 69% of patients, mosaic attenuation in 85%, lobular air-trapping in 77%, and centrilobular nodules in 54%. CTD-ILD was most often associated with peripheral or peribronchovascular fibrosis (60%), an NSIP-like pattern in 70%, ground-glass opacity in 65%, and traction bronchiectasis in 55%. Comparative analysis demonstrated statistically significant differences in zonal distribution and ancillary features among the four disease groups (p < 0.01). These findings reinforce the role of HRCT pattern recognition in narrowing the differential diagnosis of fibrotic ILD. Basal subpleural honeycombing should raise a high suspicion for IPF, while the presence of upper-lobe perilymphatic nodules is highly suggestive of sarcoidosis. The combination of mosaic attenuation, lobular air-trapping, and centrilobular nodules strongly favors fHP, whereas NSIP-like changes with peribronchovascular involvement are more typical for CTD-ILD. Integrating these imaging clues into clinical assessment may improve diagnostic accuracy, reduce the need for invasive procedures, and facilitate early, disease-specific management in patients with fibrotic ILD.