Adult exogenous lipoid pneumonia: A rare and underrecognized entity in cytology - A case series.

Background: Exogenous lipoid pneumonia (ELP) is a rare benign entity without specific clinical or imaging presentation. Although cytological studies - either bronchoalveolar lavage (BAL) or fine-needle aspiration (FNA) - may be pursued in patients with ELP, a definitive diagnosis is frequently rendered only on histology. The aim of this study is to highlight the cytological features of ELP.

Methods: A search of cytopathology (CP) and surgical pathology (SP) diagnoses of ELP was conducted. The corresponding clinical and imaging features were obtained, and the morphology, particularly the presence and size of the intracytoplasmic vacuoles and background, was assessed.

Results: Nine cases of ELP were identified, including eight with corresponding CP and SP. A neoplasm was suspected in three based on imaging, but ELP was not in the differential clinically or radiographically in any. Among the cases, six patients had BALs and three FNAs. All of the samples showed multiple large vacuoles within macrophages with at least some equal to or larger than the size of the cell nucleus. Similar vacuoles were noted extracellularly on smears.

Conclusions: ELP is typically described in case reports in the clinical or radiological literature. To the best of our knowledge, this represents the largest series of adult ELP in CP. When large vacuoles are present in macrophages in cytology specimens, at least a suspicion of ELP can be suggested to initiate appropriate therapy, identify/remove the inciting agent, and preclude a more invasive procedure.