Lipoid Pneumonia: HRCT and MRI Spectrum, Diagnostic Pitfalls, and Imaging-Based Diagnostic Workflow—A Systematic Review

Background/Objectives: Lipoid pneumonia (LP) is a rare and frequently underdiagnosed pulmonary condition with a broad spectrum of radiological manifestations that can closely mimic infectious, inflammatory, and neoplastic lung diseases. Despite its clinical relevance, no standardized imaging-based diagnostic pathway exists. For this reason, this pictorial narrative review aims to provide a structured, imaging-centred synthesis of LP, to characterise the full spectrum of high-resolution CT (HRCT) and magnetic resonance imaging (MRI) findings, and to propose a pragmatic diagnostic workflow. Methods: A systematic literature search was performed in PubMed, MEDLINE, Embase, and the Cochrane Library from January 1950 to February 2025. Search terms combined “lipoid pneumonia” with imaging-related keywords including “HRCT,” “computed tomography,” “MRI,” and “fat attenuation.” After screening 891 deduplicated records, 60 studies were included in the narrative synthesis. Eight illustrative institutional cases with imaging–pathology correlation were additionally selected to demonstrate key imaging phenotypes. Results: HRCT is the cornerstone modality, demonstrating intralesional fat attenuation (typically −30 to −150 HU) in 40–80% of cases depending on series and disease chronicity. Additional patterns include ground-glass opacity, crazy paving, centrilobular nodules, and mass-like consolidation mimicking malignancy. Fat attenuation is absent in up to 60% of cases when inflammatory exudate or fibrosis masks lipid content. MRI, particularly chemical shift imaging, serves as a problem-solving adjunct in pseudotumoral or densitometrically equivocal presentations. A pragmatic diagnostic workflow is proposed, integrating HRCT findings, exposure history, fat-sensitive MRI in selected cases, BAL cytology, and histopathological confirmation when required. Conclusions: A pattern-based radiological approach, anchored on HRCT and integrated with clinical exposure history, BAL cytology, and selective use of fat-sensitive MRI, enables accurate diagnosis of LP in most cases and can prevent unnecessary invasive procedures including surgical resection performed under suspicion of malignancy.