May 2023 – Pulmonary Pathology

The patient is a 71-year-old woman who presented with dyspnea, chronic cough, and intermittent fever. Cross-sectional thoracic imaging demonstrated bilateral pulmonary opacities and a focal right lower lobe density on a chest CT (Figure 1; imaging). A lung biopsy was performed (Figures 2 and 3; pathology).

Figure 1: CT image, thorax, axial view
Figure 2: Right lung, 200x original magnification (hematoxylin and eosin stain)
Figure 3: Right lung, 400x original magnification (hematoxylin and eosin stain)

What is your diagnosis?

  • Viral pneumonia
  • Endobronchial lipoma
  • Exogenous lipoid pneumonia
  • Pulmonary alveolar proteinosis

The correct answer is ...

Exogenous lipoid pneumonia.

Exogenous lipoid pneumonia is a form of aspiration pneumonia caused by either the aspiration or inhalation of lipid-containing products, most often nasal decongestants or other oil-based products. More recently, this condition has been associated in case reports with vaping, which is the use of electronic cigarettes that produce an inhalable aerosol composed of nicotine, flavorants, oils, and other chemicals. These processes and etiologies are in contrast to endogenous lipoid pneumonia, which is usually associated with airway obstruction.

The biopsies in this case show alveolated parenchyma with patchy interstitial thickening and a cellular process within airspaces. Variably sized vacuoles distend the cytoplasm of reactive macrophages, occasionally forming focal multinucleated giant cells within alveolar spaces and in the interstitium. Colorless, dot-like refractile material can be identified within a subset of the vacuoles.

This histologic impression is representative of the underlying pathophysiology of this condition. As lipid material is introduced into the airspaces, it recruits a foreign-body reaction due to the accumulation of insoluble material within the cytoplasm of macrophages. This manifests as variably sized vacuoles associated with histiocytic inflammation including multinucleated foreign body-type giant cells and, in chronic conditions, reactive fibrosis.

The radiological findings in lipoid pneumonia are nonspecific, with variable patterns and distributions of consolidation. Most often, however, the lower lung fields are disproportionately affected. As such, biopsies are generally favored to establish a histological diagnosis or confirmation of a clinically suspected process. The prognosis of exogenous lipoid pneumonia is generally favorable; however, cases with significant chronicity can display irreversible parenchymal fibrosis.


  1. Beck LR, Landsberg D. Lipoid pneumonia. In: StatPearls. StatPearls Publishing; 2023.
  2. Betancourt SL, Martinez-Jimenez S, Rossi SE, Truong MT, Carrillo J, Erasmus JJ. Lipoid pneumonia: spectrum of clinical and radiologic manifestations. AJR Am J Roentgenol. 2010;194(1):103-109.
  3. Marchiori E, Zanetti G, Mano CM, Hochhegger B. Exogenous lipoid pneumonia. Clinical and radiological manifestations. Respir Med. 2011;105(5):659-666.
  4. Schwaiblmair M, Berghaus T, Haeckel T, Wagner T, Scheidt W von. [Lipoid pneumonia - an underestimated syndrome]. Dtsch Med Wochenschr. 2010;135(1-2):27-31.
Photo of Nicholas Boire, M.D., M.Sc.

Nicholas Boire, M.D., M.S.

Resident, Anatomic & Clinical Pathology
Mayo Clinic

Melanie Bois, M.D.

Consultant, Anatomic Pathology
Mayo Clinic
Assistant Professor of Laboratory Medicine and Pathology
Mayo Clinic College of Medicine and Science

MCL Education

This post was developed by our Education and Technical Publications Team.