Pictorial Essay
Cardiopulmonary Imaging
January 2010

Lipoid Pneumonia: Spectrum of Clinical and Radiologic Manifestations

Abstract

OBJECTIVE. Lipoid pneumonia results from accumulation of lipids in the alveoli and can be either exogenous or endogenous in cause based on the source of the lipid. Exogenous lipoid pneumonia is caused by inhalation or aspiration of animal fat or vegetable or mineral oil. Endogenous lipoid pneumonia is usually associated with bronchial obstruction. The purpose of this article is to review the pathogenesis and clinical and radiologic manifestations of exogenous and endogenous lipoid pneumonia.
CONCLUSION. The ability to recognize the radiologic manifestations of lipoid pneumonia is important because, in the appropriate clinical setting, these findings can be diagnostic.

Introduction

Lipoid pneumonia is uncommon and, although it is difficult to determine the precise clinical incidence, autopsy series have reported a frequency of only 1.0–2.5% [1]. However, it is important to be aware of the various radiologic manifestations of lipoid pneumonia because, in the appropriate clinical setting, these findings can be diagnostic. Unfortunately, lipoid pneumonia can mimic the clinical and radiologic features of other diseases including primary lung carcinoma, and histopathologic confirmation of the diagnosis may be necessary.
Lipoid pneumonia can be either exogenous or endogenous in cause based on the source of the lipid. Exogenous lipoid pneumonia usually occurs when animal fats or mineral or vegetable oils are aspirated or inhaled [1], whereas endogenous lipoid pneumonia results from lipid accumulation within intraalveolar macrophages in the setting of bronchial obstruction, chronic pulmonary infection, pulmonary alveolar proteinosis, or fat storage diseases [2]. Because awareness and understanding of lipoid pneumonia are essential in improving diagnostic interpretation and appropriate patient management, we review the pathogenesis and clinical and radiologic manifestations of lipoid pneumonia.

Exogenous Lipoid Pneumonia

Exogenous lipoid pneumonia, initially described in 1925 by Laughlen in four patients with a prolonged history of laxative ingestion and use of oil-based nose drops, can be acute or chronic in presentation [1].
Acute exogenous lipoid pneumonia is uncommon and typically is caused by an episode of aspiration of a large quantity of a petroleum-based product [3, 4] (Fig. 1). Although acute pneumonitis after aspiration of petroleum-based products typically occurs in children due to accidental poisoning, acute exogenous lipoid pneumonia also occurs in performers (fire-eaters) who use liquid hydrocarbons for flame blowing.
Chronic exogenous lipoid pneumonia usually results from repeated episodes of aspiration or inhalation of animal fat or mineral or vegetable oils over an extended period. Although chronic exogenous lipoid pneumonia typically occurs in older patients, it also has been reported in children, especially those with a predisposition to aspiration, including mental retardation and cleft palate, as well as in infants when mineral oil is used as a lubricant to facilitate feeding [1]. Chronic exogenous lipoid pneumonia also can occur in patients without a predisposing anatomic or functional abnormality in swallowing. The aspiration of fats or oils has been reported in patients with a history of chronic use of mineral oil or petroleum-based lubricants and decongestants such as Vaseline (Unilever), Vicks VapoRub, and lip gloss [1, 5] (Fig. 2A, 2B).
Chronic exogenous lipoid pneumonia also can result from inhalation of mineral oil and has been described in a variety of industrial occupations, including those involved in the lubrication and cleaning of machinery and the spraying of pesticides or paints [6]. Additionally, chronic exogenous lipoid pneumonia has been reported as a result of embolization after rectal or subcutaneous administration of mineral oils [7].

Pathophysiology

The development of parenchymal abnormalities in lipoid pneumonia is dependent on the type, amount, frequency, and length of time of aspirated or inhaled oils or fats. Mineral oil (a mixture of inert, long-chain, saturated hydrocarbons obtained from petroleum) and vegetable-based oils tend to cause minimal to mild inflammatory reactions (Fig. 3A, 3B). The intraalveolar oils can coalesce in the alveoli and become encapsulated by fibrous tissue, resulting in a nodule or mass (paraffinoma) (Fig. 4A, 4B).
Conversely, animal fats are hydrolyzed by lung lipases into free fatty acids that trigger a severe inflammatory reaction that manifests as focal edema and intraalveolar hemorrhage [5]. Fatty acids either remain in the alveolar spaces or are phagocytosed by macrophages that then migrate to the interlobular septa. Regardless of location, the inflammatory response can destroy the alveolar walls and the interstitium, and the resultant fibrosis can occasionally progress to end-stage lung disease.

Clinical Findings

Acute exogenous lipoid pneumonia typically manifests clinically as cough, dyspnea, and low-grade fever that usually resolve with supportive therapy [1]. In contrast, patients with chronic exogenous lipoid pneumonia are frequently asymptomatic on presentation and are only identified because of an incidentally detected abnormality on radiologic imaging. Most of these patients are elderly (sixth or seventh decade of life); have an anatomic or functional alteration to swallowing, with a predisposition to aspiration; and have a history of topical application or ingestion of lipids [1]. However, a history of exposure to animal fats or mineral or vegetable oils may not be elicited, and a careful clinical history to identify the source of aspirated or inhaled lipid may be required. Symptomatic patients most frequently present with chronic cough or dyspnea. Although fever, weight loss, chest pain, and hemoptysis are less common at presentation [1, 2], Gondouin et al. [8] reported fever and weight loss in 39% and 34% of patients, respectively. Auscultation of the lungs is normal in most patients but can reveal crepitations or wheezes [1].

Radiologic Manifestations

Acute exogenous lipoid pneumonia can manifest radiologically within 30 minutes of the episode of aspiration or inhalation, and pulmonary opacities can be seen in most patients within 24 hours [9]. The opacities are typically ground-glass or consolidative, bilateral, and segmental or lobar in distribution and predominantly involve the middle and lower lobes [10] (Fig. 5A, 5B). Other manifestations of acute exogenous lipoid pneumonia include poorly marginated nodules, pneumatoceles, pneumomediastinum, pneumothorax, and pleural effusions [9, 10]. Pneumatoceles usually occur within regions of ground-glass or consolidative opacities, typically manifest radiologically within 2–30 days after aspiration or inhalation, and are more common in patients who have aspirated or inhaled a large amount of mineral oils or petroleum-based products [11]. Pneumothorax and pneumomediastinum are rare and have been reported to occur within 4 days after hydrocarbon aspiration. Importantly, they are associated with a poor prognosis.
CT can reveal areas of fat attenuation as low as –30 HU within the consolidative opacities and nodules, a finding diagnostic of lipoid pneumonia. However, even though the attenuation of the opacities or nodules can be low at initial presentation, the presence of superimposed inflammation can be a confounding factor by increasing the attenuation so that the fat component becomes less conspicuous or obscured [1, 10, 12].
The radiologic manifestations of acute exogenous lipoid pneumonia typically improve or resolve over time. Resolution of opacities is variable and usually occurs within 2 weeks to 8 months [3]. Typically, resolution is complete, although minimal scarring can occur.
Similar to acute exogenous lipoid pneumonia, chronic exogenous lipoid pneumonia most frequently manifests as ground-glass or consolidative opacities involving one or more segments, typically with a peribronchovascular distribution and predominant involvement of the lower lobes (Fig. 6). Architectural distortion associated with the consolidative opacities has been reported, and thickening of the interlobular septa or fibrosis in the adjacent lungs can occur in the later stages due to the transportation of oils from the alveoli into the lung interstitium (Fig. 7). Additionally, ground-glass opacities with associated interlobular septal thickening (crazy-paving pattern) with a basilar predominance have also been described.
Characteristically, chronic exogenous lipoid pneumonia manifests as an adipose-containing mass [1] (Fig. 8). Although the mass is typically irregular or spiculated as a result of chronic inflammation and secondary fibrosis, the presence of fat in the mass is, with a few exceptions, a diagnostic feature of exogenous lipoid pneumonia. Specifically, hamartomas and lung metastases from primary extrathoracic sarcomas such as chondrosarcomas or liposarcomas can manifest as fat-containing lung nodules. Cavitation and calcification of the mass occasionally can occur.
Other manifestations of chronic exogenous lipoid pneumonia are single or multiple nodules or masses that may or may not contain fat (Fig. 9). In the absence of fat, the nodules or masses can be indistinguishable from primary lung cancer [1316]. Furthermore, because of the inflammatory component, lipoid pneumonia can have increased uptake of 18F-FDG on PET and can thus be misinterpreted as malignancy [17]. The radiologic manifestations of chronic exogenous lipoid pneumonia can improve slowly over time but typically remain stable even if the exposure to vegetable or mineral oils or animal fats is discontinued [1]. Fibrosis and destruction of normal lung architecture can result in cor pulmonale.

Endogenous Lipoid Pneumonia

Endogenous lipoid pneumonia, also called “cholesterol pneumonia” or “golden pneumonia,” is an obstructive pneumonitis. Endogenous lipoid pneumonia is a histopathologic diagnosis made on the basis of the characteristic appearance of the obstructive pneumonitis. Macroscopically, there is parenchymal consolidation that has a characteristic yellowish discoloration due to the accumulation of lipid in the alveoli [18]. Histologically, there is an accumulation of lipid-filled macrophages and eosinophilic proteinaceous material derived from degenerating cells, including surfactant from type II pneumocytes, in the alveoli distal to the bronchial obstruction.
Polarized light microscopy after staining with sulfuric acid and acetic acid (Schultz stain) usually reveals cholesterol crystals, a finding diagnostic of endogenous lipoid pneumonia. Endogenous lipoid pneumonia typically manifests radiologically as consolidative opacities distal to a central obstructing lesion [19] (Fig. 10A, 10B, 10C). However, unlike exogenous lipoid pneumonia, the accumulation of lipid-rich cellular debris does not manifest radiologically as lipid-containing opacities with low attenuation typical of lipid.
Historically, endogenous lipoid pneumonia typically has been reported as being caused by non–small cell lung cancers but also can occur as a manifestation of infection and other diseases that are not associated with bronchial obstruction. In this regard, an association between endogenous lipoid pneumonia and repetitive episodes of fungal pneumonia recently has been reported [20]. Additionally, in pulmonary alveolar proteinosis (PAP), the alveoli are usually filled with protein and lipid material resembling surfactant. PAP typically manifests on CT as ground-glass opacities, often with superimposed thickening of the interlobular and intralobular interstitia (crazypaving pattern) [18]. Niemann-Pick disease, a lipid-storage disorder in which accumulation of intraalveolar and interstitial fat-laden macrophages and sphingomyelin occurs, is also within the spectrum of endogenous lipoid pneumonia. The radiologic manifestations of Niemann-Pick disease include diffuse ground-glass opacities and thickening of interlobular and intralobular interstitia, as well as centrilobular nodular opacities [21].

Conclusion

Lipoid pneumonia can be either exogenous or endogenous in cause, and awareness of these two different entities is important in clinical practice. In addition, knowledge of the various ways that a patient can be exposed to lipid-containing material can help to solicit a clinical history of lipid aspiration or inhalation and facilitate the diagnosis of exogenous lipoid pneumonia. In fact, this information, together with the ability to recognize the range of manifestations of exogenous lipoid pneumonia, is essential in the diagnosis of this entity. In this regard, although the radiologic findings of exogenous lipoid pneumonia can be nonspecific, lipid-containing opacities on CT images are diagnostic if there is a history of use or occupational exposure to lipid-containing materials.
In contradistinction, endogenous lipoid pneumonia usually occurs as a result of bronchial occlusion and typically manifests as an obstructive pneumonitis containing lipid distal to a centrally located mass. However, unlike exogenous lipoid pneumonia, the accumulation of lipid-rich cellular debris does not manifest radiologically as lipid-containing opacities, and the diagnosis is histopathologic. Several other entities, including pulmonary infections, lipid storage diseases, and pulmonary alveolar proteinosis are considered within the spectrum of endogenous lipoid pneumonia. The imaging findings in these diseases vary, and the clinical and histologic findings are often necessary to confirm the diagnosis.
Fig. 1 Acute exogenous lipoid pneumonia in 54-year-old woman after episode of aspiration of large volume of mineral oil. High-resolution CT image shows geographic distribution of ground-glass opacities and associated thickening of interlobular septa (crazy-paving pattern). Note that although opacities may be present soon after aspiration, radiologic manifestations of acute exogenous lipoid pneumonia can take up to 24 hours to develop.
Fig. 2A Chronic exogenous lipoid pneumonia due to repeated episodes of aspiration of mineral oil in 65-year-old woman with scleroderma manifesting as progressive dyspnea and nonproductive cough. Axial CT image (coned view) of right lower lobe shows geographic distribution of ground-glass opacities with associated interlobular septal thickening.
Fig. 2B Chronic exogenous lipoid pneumonia due to repeated episodes of aspiration of mineral oil in 65-year-old woman with scleroderma manifesting as progressive dyspnea and nonproductive cough. Photomicrograph shows intraalveolar and interstitial accumulation of lipid-laden macrophages (arrows), characteristic pathologic manifestation of lipoid pneumonia. (H and E, original magnification ×100)
Fig. 3A Chronic exogenous lipoid pneumonia in 63-year-old woman due to chronic aspiration of Vaseline (Unilever) petroleum-based lubricant. Axial CT image shows consolidative and ground-glass opacities bilaterally. Note mild architectural distortion associated with consolidative opacities in left lower lobe.
Fig. 3B Chronic exogenous lipoid pneumonia in 63-year-old woman due to chronic aspiration of Vaseline (Unilever) petroleum-based lubricant. CT image shows areas of fat attenuation within consolidation (arrows), finding diagnostic of lipoid pneumonia.
Fig. 4A Exogenous lipoid pneumonia in asymptomatic 80-year-old man due to chronic aspiration of mineral oil manifesting as nodule (paraffinoma). Coronal CT image shows spiculated left upper lobe nodule (arrow) and nodular opacities in left lower lobe. Note spiculation, typically indicative of malignancy, is due to inflammatory reaction incited by mineral oil.
Fig. 4B Exogenous lipoid pneumonia in asymptomatic 80-year-old man due to chronic aspiration of mineral oil manifesting as nodule (paraffinoma). Coronal CT image shows fat attenuation within nodule (arrows), diagnostic of chronic lipoid pneumonia.
Fig. 5A Exogenous lipoid pneumonia in 56-year-old woman with history of partial gastrectomy and single episode of mineral oil aspiration. Chest radiograph shows ground-glass opacities (arrows) in right lung.
Fig. 5B Exogenous lipoid pneumonia in 56-year-old woman with history of partial gastrectomy and single episode of mineral oil aspiration. Coronal high-resolution CT image shows ground-glass opacities with superimposed interlobular thickening bilaterally (crazy-paving pattern). Biopsy revealed intraalveolar fat globules, confirming diagnosis of lipoid pneumonia.
Fig. 6 Exogenous lipoid pneumonia in 80-year-old man resulting from chronic aspiration of mineral oil. Axial CT image shows consolidation and ground-glass opacities in middle lobe and focal nodular opacities in left lower lobe. Note that although exogenous lipoid pneumonia typically has predominant lower lobe involvement, all lobes can be affected.
Fig. 7 Exogenous lipoid pneumonia in 53-year-old man due to chronic aspiration of petroleum-based lubricant (Vaseline, Unilever). Axial CT image shows masslike consolidative opacity in middle lobe (arrows) and scattered consolidative and ground-glass opacities in right lower lobe and left lung. Note mild architectural distortion associated with consolidative opacity in middle lobe is result of inflammation and scarring that occur due to transportation of oil from alveoli into lung interstitium.
Fig. 8 Exogenous lipoid pneumonia in 78-year-old woman with history of chronic constipation and ingestion of vegetable oil laxative daily. Axial CT image shows irregular masslike opacity (arrows) in middle lobe. Note fat attenuation within mass. Presence of fat is diagnostic feature of exogenous lipoid pneumonia.
Fig. 9 Exogenous lipoid pneumonia in 42-year-old woman with history of colon cancer, constipation, and chronic ingestion of oil laxatives. Axial CT image (coned view) shows multiple left lower lobe nodules with fat attenuation (arrows), consistent with lipoid pneumonia.
Fig. 10A Endogenous lipoid pneumonia in 49-year-old man due to central bronchial obstruction who presented with 6-week history of hemoptysis and fever. (Courtesy of Madewell JE, The University of Texas M. D. Anderson Cancer Center, Houston, TX) Chest radiograph shows masslike consolidation (arrows) in right lung.
Fig. 10B Endogenous lipoid pneumonia in 49-year-old man due to central bronchial obstruction who presented with 6-week history of hemoptysis and fever. (Courtesy of Madewell JE, The University of Texas M. D. Anderson Cancer Center, Houston, TX) Photograph of gross pathologic specimen after partial right upper lobe resection shows well-circumscribed consolidation that has characteristic white-yellow discoloration due to accumulation of lipid in alveoli (arrows).
Fig. 10C Endogenous lipoid pneumonia in 49-year-old man due to central bronchial obstruction who presented with 6-week history of hemoptysis and fever. (Courtesy of Madewell JE, The University of Texas M. D. Anderson Cancer Center, Houston, TX) Photomicrograph shows lipid-filled macrophages (asterisks). Note that after staining with sulfuric acid and acetic acid (Schultz stain) (not shown), polarized light microscopy revealed cholesterol crystals consistent with diagnosis of endogenous lipoid pneumonia. (H and E, ×40)

Footnote

Address correspondence to S. L. Betancourt ([email protected]).

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Information & Authors

Information

Published In

American Journal of Roentgenology
Pages: 103 - 109
PubMed: 20028911

History

Submitted: May 9, 2009
Accepted: June 14, 2009

Keywords

  1. aspiration
  2. endogenous lipoid pneumonia
  3. exogenous lipoid pneumonia

Authors

Affiliations

Sonia L. Betancourt
Division of Diagnostic Imaging, Department of Diagnostic Radiology, The University of Texas M. D. Anderson Cancer Center, Unit 0371, 1515 Holcombe Blvd., Houston, TX 77030.
Santiago Martinez-Jimenez
Department of Diagnostic Radiology, Duke University Medical Center, Durham, NC.
Santiago E. Rossi
Centro de Diagnostico Enrique Rossi, Buenos Aires, Argentina.
Mylene T. Truong
Division of Diagnostic Imaging, Department of Diagnostic Radiology, The University of Texas M. D. Anderson Cancer Center, Unit 0371, 1515 Holcombe Blvd., Houston, TX 77030.
Jorge Carrillo
Departmento de Radiologia, Universidad Nacional de Colombia, Hospital Universitario Mayor, Bogota, Colombia.
Jeremy J. Erasmus
Division of Diagnostic Imaging, Department of Diagnostic Radiology, The University of Texas M. D. Anderson Cancer Center, Unit 0371, 1515 Holcombe Blvd., Houston, TX 77030.

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