An Experimental Study of Exo genous Lipoid Pneumonia: Sequential Changes in High-Resolution CT and MR Findings

ABSTRACT

PURPOSE: To evaluate sequential changes in high-resolution CT(HRCT) and MR findings of exogenous lipoidpneumonia in rabbits and to compare the radiologic and histopathologic findings. MATERIALS AND METHODS: A singleendobronchial administration of shark liver oil(0.5 or 1 ml/kg of body weight) was given to 25 rabbits. HRCT scanswere obtained immediately(n=17), at 1 day(n=14), 3 days(n=10), 1 week(n=15), 2 weeks(n=10), 4 weeks(n=9), 6weeks(n=5), 8 weeks(n=6), 10 weeks(n=4), 12 weeks(n=2), 14 weeks(n=3), and 16 weeks(n=2) after administration.Changes in distribution, extent, and attenuation were assessed on HRCT scans. MR scans were obtainedimmediately(n=12), at 1 day(n=9), 3 days(n=9), 1 week(n=15), 2 weeks(n=9), 4 weeks(n=11), 6 weeks(n=5), 8weeks(n=7), 10 weeks(n=3), 14 weeks(n=3), and at 16 weeks(n=2) after administration. Changes in distribution,extent, and signal intensity were assessed on MR scans. In 16 rabbits, CT and MR findings were compared withhistopatholo-gic findings obtained in the same plane. RESULTS: HRCT findings included consolidation withair-bronchogram, ground-glass attenuation and fat attenuation within the lesion at earlier stages(immediate-2weeks). The extent of lesions was greatest at 1 week, and was then seen to gradually decrease on follow-up CTscans. T1-weighted MR images(T1WI) showed high or intermediate signal intensity(SI) at earlier stages andintermediate SI at later stages, while T2-weighted MR images(T2WI) showed high SI at both earlier and laterstages. Histopathologic correlation showed that ground-glass attenuation and consolidation on HRCT reflectedintraalveolar lipid-laden macrophages, cuboidal metaplasia of alveolar epithelial cells, and alveolar septalwidening with inflammatory cell infiltration. Maximal infiltration of oil in the lung correlated closely with thepeak low-attenuation seen on CT scans and the high signal intensity seen on T1WI. CONCLUSION: Shark liveroil-induced exogenous lipoid pneumonia in rabbits is reliably diagnosed by HRCT and MR during earlier stages(1-2weeks). The absence of fat at later stages cannot exclude for certain a diagnosis of exogenous lipoid pneumonia.