Squalene-Induced Lipoid Pneumonia in Rabbits: High-Resolution CT and Pathologic findings

ABSTRACT

PURPOSE: To describe the HRCT and pathologic findings of squalene-induced lipoid pneumonia in rabbits. MATERIALS AND METHODS: Three ml of squalene was instilled into the trachea between the second and the third tracheal ring in 16 rabbits. Serial HRCT scans were obtained on day 4 (n=8), at 1 week (n=7), 2 weeks (n=1), 4 weeks(n=1), 6 weeks (n=2) and 20 weeks (n=1) after squalene instillation. With sacrifice of the rabbits pathology was reviewed at 1 week (n=3), 4 weeks (n=3), and 6 weeks (n=4) after CT scans. RESULTS: Lipoid pneumonia was induced in 8 rabbits; lesions were distributed mainly in the dependent posterior lung. On serial HRCT scans, airspace consolidation, as seen on an air-bronchogrm, and nodular opacities were early findings; these gradually diminshed and with time were replaced by nodular & linear opacities. Histologically, pulmonary fibrosis appeared one week after squalene instillation and progressed over time. Alveolar septal thickening and cuboidal change of the alveolar lining epithelium were more prominent at week 6. CONCLUSION: The early change of squalene-induced lipoidpneumonia in rabbits is the proliferation of intraalveolar macrophage, which is responsible for air-space consolidation with air-bronchograms on HRCT. Nodular and linear opacities on HRCT are due to the appearance of pulmonary fibrosis one week after squalene instillation, and its subsequent progression.