Exogenous Lipoid Pneumonia

Introduction: Exogenous lipoid pneumonia refers to lung lesions that develop following aspiration or inhalation of animal, vegetable, or mineral oils. An engaging account of the circumstances under which aspiration of lipoid material occurs is found in the reference by Spickard and Hirschmann [1]. Lipoid material glides down the respiratory tract without stimulating cough and is not removed effectively by the cilia. Animal fats, which can be hydrolyzed to fatty acids cause more inflammation than vegetable or mineral oils, but all types stimulate a chronic granulomatous inflammation, which tends to be located in the lower or middle lobes.

Clinical features: Patients present with an abnormal chest radiograph (50%) or symptoms of pneumonia. Radiographs and CT often show solitary nodules or masses, which may resemble cancer. A CT showing attenuation between -30 and -150 HU in the lesion is consistent with the diagnosis, but not specific [1,2]. Staining of BAL fluid with oil red O can be diagnostic if the physician has considered aspiration and alerts the pathologist. The disease is potentially reversible if the causative agent is discontinued. Occasionally, superinfection with bacteria occurs, and lung cancer is a rare sequela [1].

Histologically, the lipid-laden macrophages have vacuoles of different sizes. In paraffin sections, stains for fat are negative, as it is dissolved during embedding. The diagnosis must be made on frozen sections stained with oil red O.

Oil red O stain of lavage fluid

Several types of cells are present in this smear. Only macrophages staining positively (arrows) are counted. The cell at the lower right may also be a macrophage. The smaller cells; e.g., that at the upper left, are PMNs, which stain non-specifically with the oil red O.

Endogenous lipoid pneumonia: In contrast to exogenous disease, endogenous lipoid pneumonia refers to an accumulation of lung-produced lipoid material caused by poor clearance (BOOP, around neoplasms). It is also called golden cholesterol pneumonia because of its yellow color grossly when there are large accumulations. The endogenous form also occurs as a metabolic abnormality in amiodarone toxicity or rarely in lipid storage diseases.

References

1. Spickard III A, Hirschmann J. Exogenous lipoid pneumonia. Arch Intern Med 1994; 154:686-692.

2. Lee K, Müller N, Hale V, Newell Jr J, Lynch D, Im J-G. Lipoid pneumonia: CT findings. J Comput Assist Tomogr 1995; 19:48-51.

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