INTRODUCTION: Exogenous lipoid pneumonia (ELP) is caused by the inhalation of animal fats, vegetable or mineral oil. It is commonly seen in patients at high risk for aspiration and in those using mineral oil as a laxative. Appearance on chest imaging is variable, but focal consolidation mimicking tumor may be seen. Though classically confined only to the lung field, we present an unusual case of ELP initially misdiagnosed as stage IV lung cancer.
CASE PRESENTATION: A 72 year old female with a history of achalasia was referred to the thoracic oncology clinic for evaluation after a chest CT obtained to evaluate chest pain revealed spiculated masses in the right upper and lower lobes with hilar adenopathy. A dilated esophagus containing particulate food matter was also noted. Subsequent PET-CT showed the pulmonary lesions to be FDG avid with SUVmax between 5.3 and 6.2 with avidity also seen in the hilar nodal stations. A strongly avid (SUVmax=40) lytic lesion of the L5 vertebral body was also identified, concerning for a metastatic pulmonary malignancy. To establish a tissue diagnosis, the right upper and lower lobe masses were biopsied transbronchially using electromagnetic navigational bronchoscopy revealing foamy histiocytes and no evidence of malignancy. The hilar lymph nodes were sampled under endobronchial ultrasound guidance and similarly revealed no malignant tissue. This lipoid pneumonia is likely the result of chronic aspiration secondary to the patient’s profound achalasia. Interestingly, no history of aspiration was given. The patient used gel fish-oil capsules but no other lipid rich medications or foods. A biopsy of the L5 vertebral body was also obtained, revealing a highly cellular infiltrate with a monomorphic population of plasma cells consistent with a plasmacytoma. She has subsequently completed a course of treatment with 3500 cGy radiotherapy and 4 cycles of zoledronic acid and is doing well.
DISCUSSION: The term lipoid pneumonia was initially used by Laughlin in 1925 to describe the presence of lipid laden macrophages in lung tissue. This entity has since been divided into endogenous and exogenous categories, describing the route of lipid entry into the lung. Endogenous lipoid pneumonia is felt to represent a post-obstructive state wherein cholesterol and other lipids are released by necrotic tissue distal to the airway obstruction. Conversely, exogenous lipoid pneumonia (ELP) results from the inhalation, aspiration or other absorption of fats or oils. Presentation is quite variable and aspiration events are often asymptomatic as the lipid rich substances frequently do not trigger a cough reflex. Patients will often have insidious onset of cough and infectious symptoms such as fever. Radigraphic findings are varied, with lesions often FDG avid. Biopsy of the lesions reveals lipid laden macrophages and vacuoles may be seen in advanced lesions. Treatment involves primarily supportive care, though corticosteroid use has been described to blunt the inflammatory cascade in patients with acute respiratory distress.
CONCLUSIONS: Lipoid pneumonia, though rare, can produce imaging findings similar to pulmonary malignancy. History of aspiration, use of mineral oil laxatives, or esophageal motility disorders should increase suspicion for this disease entity. This case illustrates the ease with which a benign process may be mistaken for advanced malignancy on chest imaging and the importance of continued advancement of techniques for safe pulmonary biopsy.
Reference #1 Exogenous lipoid pneumonia: serial chest plain roentgenography and high-resolution computerized tomography findings. Chiang IC, Lin YT, Liu GC, Chiu CC, Tsai MS, Kao EL. Kaohsiung J Med Sci. 2003 Dec;19(12):593-8.
Reference #2 Exogenous lipid pneumonia: a retrospective multicentre study of 44 cases in France. Gondouin A, Manzoni P, Ranfaing E, Brun J, Cadranel J, Sadoun D, Cordier JF, Depierre A, Dalphin JC. Eur Respir J. 1996 Jul;9(7):1463-9
DISCLOSURE: The following authors have nothing to disclose: David Odell, Sidharta Gangadharan, Gaetane Michaud
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