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).
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.
Nicholas Boire, M.D., M.S.
Resident, Anatomic & Clinical Pathology
Melanie Bois, M.D.
Consultant, Anatomic Pathology
Assistant Professor of Laboratory Medicine and Pathology
Mayo Clinic College of Medicine and Science