Thoracic Pathology: A Volume in the High Yield Pathology Series 1st Edition

Lipoid Pneumonia

Definition

• Two types:

  • Exogenous lipoid pneumonia is the accumulation of aspirated oils within the alveoli and subsequent foreign body reaction

  • Endogenous lipoid pneumonia, also called cholesterol pneumonia or golden pneumonia, is a localized accumulation of lipid-laden macrophages within alveolar spaces distal to an obstructed airway

Pathogenesis

• Exogenous lipoid pneumonia: repeated episodes of aspiration/inhalation of fat or oils results in their accumulation within alveolar macrophages that are incapable of metabolizing the fatty substances; therefore, oil is repeatedly released into the alveoli, eliciting a foreign body reaction. Mineral oil is the most common irritant because it can inhibit the cough reflex and ciliary motility, thus facilitating silent inhalation

• Endogenous lipoid pneumonia: obstruction results in the accumulation of cellular breakdown products, including cholesterol and its esters, from destroyed alveolar cell walls. These difficult to digest lipids are phagocytosed by macrophages, which then accumulate within the alveolar spaces

Clinical features

Epidemiology

• Reported in 1% to 2.5% of autopsies. The endogenous type is considerably more common than the exogenous type

• Endogenous lipoid pneumonia typically occurs in the setting of obstruction by tumor, bronchiolitis obliterans, or after chemotherapy or radiotherapy. It has also been reported in association with fungal pneumonia, tuberculosis, pulmonary alveolar proteinosis, and Niemann-Pick disease. Occasionally, it can be idiopathic

• Acute exogenous lipoid pneumonia occurs in children due to accidental poisoning or in performing fire-eaters who use liquid hydrocarbons for flame blowing

• Risk factors for chronic exogenous lipoid pneumonia include

  • Chronic ingestion of mineral oil for constipation (usually children and elderly) or use of oil-based nasal drops

  • Chronic topical application of petroleum-based products such as Vaseline, Vicks VapoRub, or lip gloss

  • Predisposition to aspiration (e.g., mental retardation or cleft palate)

  • Difficulty swallowing

  • Occupations involving spraying of oil-based products such as pesticides, paints, or machinery lubricants

Presentation

• Approximately 50% of patients are asymptomatic, and discovery is due to incidental imaging findings, including ground-glass opacities or single to multiple nodules (paraffinomas). The masses may not contain fat; therefore, the radiological concern of malignancy is present

• Symptoms vary and may include chronic coughing, dyspnea, hemoptysis, fever, weight loss, or chest pain

Prognosis and treatment

• Removal of the offending agent and correction of any underlying defect that may favor aspiration

• Oral steroids result in improvement of chest radiographic abnormality

• Diffuse exogenous lipoid pneumonia is treated with prednisone and, in severe cases, with whole lung lavage

• Prognosis depends on amount of irreversible fibrosis

Pathology

Gross

• Exogenous lipoid pneumonia

  • Firm gray, irregular nodule(s)

  • Greasy cut surface

  • May have prominent lymphatics on lung surface

• Endogenous lipoid pneumonia

  • Consolidated area

  • Creamy tan to golden yellow discoloration

  • Bronchial obstruction proximal to lesion

Histology

• Exogenous lipoid pneumonia

  • Early lesions: intraalveolar lipid-laden macrophages and almost normal alveolar walls and septae

  • Advanced lesions:

    – Multiple round to oval cystic spaces (lipid vacuoles that are washed out during processing) surrounded by varying amounts of histiocytes and multinucleated foreign body giant cells

    – Fat vacuoles are large compared with the fine vacuoles seen in endogenous lipoid pneumonia

    – Reactive type II pneumocytic hyperplasia

    – Inflammatory infiltrates within alveolar walls, bronchial walls, and septae

  • Old lesions: fibrosis and parenchymal destruction around large lipid-containing vacuoles forming a masslike lesion

• Endogenous lipoid pneumonia

  • Intraalveolar accumulation of foamy macrophages containing fine lipid vacuoles (less than 1 micron)

  • Cholesterol clefts

  • Mild lymphoplasmacytic infiltrate and minimal fibrosis

  • May have occasional foreign body giant cells

  • Reactive type II pneumocytic hyperplasia

Immunopathology/special stains

• Oil red O or Sudan black stains highlight lipid-laden macrophages

• Sudan black stain highlights lipids in both exogenous and endogenous pneumonia; osmium tetroxide stains lipids in the endogenous form only

Main differential diagnosis

• Infectious pneumonia

• Pseudolipoid pneumonia: air-bubble artifact associated with the collapse of airspace

• Endogenous: amiodarone toxicity

• Exogenous: nontuberculous mycobacterial infection

image

Fig 1 Lipoid pneumonia. Organizing pneumonia and endogenous lipoid pneumonia in a patient with blastomycosis.

image

Fig 2 Lipoid pneumonia. Endogenous lipoid pneumonia with finely vacuolated macrophages filling the alveolar space.

image

Fig 3 Lipoid pneumonia. Postobstructive endogenous lipoid pneumonia in a patient with squamous cell carcinoma.

image

Fig 4 Lipoid pneumonia. Large lipid vacuoles are seen here in this case of exogenous lipoid pneumonia.

image

Fig 5 Lipoid pneumonia. Exogenous lipoid pneumonia: high-power view of multinucleated giant cells and macrophages containing large lipid droplets.

image

Fig 6 Lipoid pneumonia. Frozen section of a lung mass revealed macrophages filled with large lipid vacuoles consistent with exogenous lipoid pneumonia.



If you find an error or have any questions, please email us at admin@doctorlib.info. Thank you!