Lipid pneumonia is an uncommon clinical entity in which respiratory architecture is impaired, either as a result of aspiration or accumulation of lipids from different sources (exogenous and endogenous, respectively). Respiratory signs and symptoms are nonspecific. Imaging studies and a detailed patient history are vital components of the diagnostic workup.
Lipid pneumonia can arise from two pathways: After topical application and/or repeated aspiration of lipids from food and other products containing lipids (exogenous lipid pneumonia), or due to the breakdown of fats into free fatty acids in the bronchial tree (endogenous lipid pneumonia) . Based on the clinical presentation, lipid pneumonia may be further divided into acute and chronic  . Acute exogenous lipid pneumonia is most frequently diagnosed in patients who aspirate a significant quantity of lipids (such as vaseline used for topical application or fat-rich mineral, animal or vegetable oils), the majority being elderly individuals in their sixth or seventh decades or children, many of whom have some pre-existing condition that predisposes them to aspiration  . Dyspnea, cough, and low-grade fever are main symptoms that appear within the first hour after introduction of lipids into the lungs  , whereas chest pain, weight loss, and hemoptysis may be seen in more severe cases, when even respiratory failure and death may occur in the absence of adequate management and a delayed diagnosis  . Aspiration of smaller contents of fat is mostly asymptomatic, which is typical for chronic forms of the disease, and the diagnosis is often made incidentally, but chronic persistent cough and dyspnea accompanied by weight loss may appear . Endogenous lipid pneumonia has a similar clinical presentation, and it is associated with various conditions - Niemann-Pick disease, infections, non-small cell lung cancers, and pulmonary alveolar proteinosis (PAP) .
Because symptoms of lipid pneumonia are non-specific and may mimic various other respiratory diseases (infections, malignancies, autoimmune disorders, etc.), a thorough diagnostic workup is mandatory, as lipid pneumonia is often diagnosed after a significant delay in many patients . Having in mind the fact that auscultation of the lungs may frequently reveal no pathological findings (although wheezing or crepitations can be noted in severe cases), a detailed patient history is perhaps the most important part of the assessment of respiratory symptoms. Recent or chronic use of topical fat-containing creams or drugs or the appearance of symptoms after consumption of fat-rich foods, especially in elderly and children, is a valuable information. Imaging studies, however, are vital in order to distinguish fat accumulation from tumors or focal infections, and plain radiography, but more commonly, computed tomography (CT) are widely recommended early on    . Pulmonary opacities are seen after 24 hours in virtually all patients who develop acute symptoms, and their appearance depends on the extent of aspirated or accumulated fat. In most cases, ground-glass or consolidative opacities that are distributed segmentally or within a pulmonary lobe, usually in the middle or lower segments, are typical for lipid pneumonia, whereas pneumatoceles, pneumothorax, pleural effusions and pneumomediastinum may also be encountered, indicating a poorer prognosis  . CT of the chest can distinguish lipid structures due to their low attenuation and thickening of the intralobular septa, known as "crazy paving pattern" . Magnetic resonance imaging (MRI) is sometimes employed when CT and radiography yield inconclusive findings, but the use of bronchoalveolar lavage (BAL) or bronchoscopy as a tool to obtain a viable sample for biopsy was necessary for a significant number of patients, and histopathological confirmation of lipid droplets in alveoli and local macrophages serves as a definite method   .