Lipid pneumonia associated with mineral oil use presenting as fluorine-18-fluorodeoxy-D-glucose–avid lung mass

Central MessageLipid pneumonia may enter the differential in evaluating suspected thoracic malignancy. PET/CT characteristics may provide insight into the biology of this entity and inform diagnostic considerations. Lipid pneumonia may enter the differential in evaluating suspected thoracic malignancy. PET/CT characteristics may provide insight into the biology of this entity and inform diagnostic considerations. A 57-year-old man with 120 pack-year smoking history underwent computed tomography (CT) of the chest (Figure 1), then positron-emission tomography/CT imaging (Figure 2) that demonstrated a fluorine-18-fluorodeoxy-D-glucose (FDG)-avid 4.3 × 2.2 cm consolidative right lower lobe mass (maxium standardized uptake value, 8.8), with central fat attenuation. Following nondiagnostic biopsy, video-assisted thoracoscopic wedge resection was undertaken. The Institutional Review Board of the Dana-Farber/Harvard Cancer Center approved the study protocol (No. 17-606; May 14, 2019) and publication of data. The patient provided informed written consent for the publication of the study data. Gross pathologic examination showed a subpleural yellow-tan rubbery nodule with ill-defined border (Figure 3). Histologic examination (Figure 4) showed innumerable vacuoles representing lipid material, most within the cytoplasm of macrophages and multinucleated giant cells. In the center, the lipid material was incorporated into the interstitium, associated with granulation tissue, fibrosis, and chronic inflammation. At the periphery, the bulk of lipid material was located within airspace macrophages. Upon further history, the patient related longstanding use of mineral oil as a lip/face moisturizer. The positron-emission tomography/CT characteristics of exogenous lipid pneumonia1Hadda V. Khilnani G.C. Lipoid pneumonia: an overview.Expert Rev Respir Med. 2010; 4: 799-807Crossref PubMed Scopus (89) Google Scholar,2Berg B.W. Saenger J.S. Exogenous lipoid pneumonia.N Engl J Med. 1998; 338: 512Crossref PubMed Scopus (15) Google Scholar are less comprehensively described.3Gorospe L. García-Latorre R. Ajuria-Illarramendi O. Arrieta P. Gómez-García R.M. Muñoz-Molina G.M. et al.Lipoid pneumonia mimicking multifocal lung cancer in a patient with a remote laryngectomy and a recently diagnosed lung cancer: PET/CT findings.Lung Cancer. 2018; 116: 99-101Abstract Full Text Full Text PDF PubMed Scopus (1) Google Scholar,4Nakagawara K. Sasaki M. Morinaga S. Minematsu N. Pattern of FDG-PET uptake in lipoid pneumonia simulating lung cancer.Respir Med Case Rep. 2020; 31101255PubMed Google Scholar In this case, FDG uptake was notably strongly avid at the center of the fatty lesion. This pattern of centrally strong uptake has not, to our knowledge, been previously reported. First, it further distinguishes lipid pneumonia from cancer, which often shows a relative paucity of FDG avidity centrally due to the ischemia and necrosis that develop as tumor growth outstrips blood supply. Second, it provides insight into the biology of lipid pneumonia, supporting the pathologic finding that the exogenous lipid material organizes from the center first, with fibroblastic ingrowth and incorporation of lipids into the interstitium likely accounting for increased metabolism of glucose in the lesion. This mechanism is biologically plausible; it has not been specifically studied in lipid pneumonia but it may parallel the FDG uptake in fat-attenuating areas of atherosclerosis during inflammatory phases of disease.5Tarkin J.M. Joshi F.R. Rudd J.H.F. PET imaging of inflammation in atherosclerosis.Nat Rev Cardiol. 2014; 11: 443-457Crossref PubMed Scopus (260) Google ScholarFigure 2Axial fused positron-emission tomography/computed tomography image demonstrates intense fluorine-18-fluorodeoxy-D-glucose (FDG) uptake (maximum standardized uptake value, 8.8) at the center of the lesion corresponding to the area of fat attenuation on computed tomography image.View Large Image Figure ViewerDownload Hi-res image Download (PPT)Figure 3Gross pathologic examination demonstrated a subpleural yellow-tan rubbery nodule with an ill-defined border.View Large Image Figure ViewerDownload Hi-res image Download (PPT)Figure 4Microscopic pathologic examination demonstrated the periphery of the lesion. A, Low-power magnification shows preservation of airspaces with scattered lymphoid aggregates. B, High-power magnification shows vacuolated macrophages located primarily within the airspaces. Microscopic pathologic examination also demonstrated the center of lesion. C, Low-power magnification shows near-complete replacement of the airspaces with fibroblastic reaction. D, High-power magnification shows that the fibroblastic reaction is accompanied by neovascularization, collagen deposition, and lymphoplasmacytic inflammation with innumerable lipid vacuoles of varying sizes within the cytoplasm of macrophages and giant cells (black arrows indicate a few of the innumerable lipid-laden macrophages depicted.)View Large Image Figure ViewerDownload Hi-res image Download (PPT)