Lipoid Pneumonia



Lipoid Pneumonia


Helen T. Winer-Muram, MD










Axial CECT shows the typical features of chronic lipoid pneumonia with an irregular mass-like opacity in the left lower lobe image.






Axial CECT in the same patient at the same level shows that the consolidation contains focal fat image on mediastinal windows.


TERMINOLOGY


Abbreviations and Synonyms



  • Endogenous lipid pneumonia (“golden pneumonia”) and exogenous lipid pneumonia


Definitions



  • Endogenous lipid pneumonia: Accumulation of lipid containing macrophages secondary to airway obstruction


  • Exogenous lipid pneumonia: Aspiration or inhalation of animal, vegetable, or mineral oils


IMAGING FINDINGS


General Features



  • Best diagnostic clue: Low CT attenuation areas (between -10 and -150 Hounsfield units) in consolidated lung


  • Patient position/location: Exogenous: Gravity-dependent areas and right middle lobe (RML)


CT Findings



  • Endogenous: Lipid-laden macrophages show no fatty attenuation at CT


  • Controlled exogenous lipoid aspiration in animal models, sequence of events



    • Initial: Predominant ground-glass opacities in centrilobular (less aspiration) or panlobular distribution (more aspiration)



      • HU of attenuated material low (close to attenuation of original material, -150 HU)


    • 1 week: Aspirated segment increases in density to frank consolidation



      • HU of affected segment increases (may be all water density)


    • 2-4 weeks: Aspirated segment decreases in density, returns to primarily ground-glass opacities



      • “Crazy-paving” pattern evolves during this time (due to macrophage and inflammatory cell migration to interstitial lymphatics)


      • HU of attenuated segment again decreases


      • Ground-glass opacities may completely resolve, leaving smooth interlobular septal thickening



    • 2-4 months: As ground-glass opacities evolve, fibrosis develops, volume loss (up to 50% of affected segment) common



      • Volume loss signs include vascular crowding, traction bronchiectasis, fissural displacement


    • Clinical cases will mirror this experimental sequence of events



      • Consolidation most common finding (90%)


      • Fat attenuation (80%) (fat not seen in all cases)


      • Ground-glass opacities (50%)


      • “Crazy-paving” pattern (33%)


      • Irregular-shaped mass (66%)


  • Acute vs. chronic aspiration, findings often overlap



    • Small effusions common in acute (50%), not seen with chronic


    • Masses more common in chronic (66%), not seen with acute aspiration


    • Signs of volume loss more common in chronic (80%) vs. acute (25%)


  • Fat attenuation



    • Seen with both acute and chronic lipoid aspiration


    • Acute may have larger volume of low attenuation material



      • Fat may shift to dependent lung with postural change


    • Chronic mass-like areas of aspiration often have smaller (< 10% total volume) foci of fat attenuation


    • 15-20% will not have fat attenuation



      • Percentage may actually be smaller with routine use of MDCT and thin-collimation


    • Partial volume artifact of abnormal lung admixed with air may give false-positive fat attenuation


  • Distribution



    • Gravity dependent: Posterior segments of upper lobes and superior segments of lower lobes in supine position, basilar segments in upright position


    • Right middle lobe also common for unknown reason


  • Resolution



    • Acute aspiration usually improves (80%) but rarely clears completely


    • Chronic aspiration usually stable and indolent over time


  • Complications



    • Superinfection with atypical mycobacteria (usually M. fortuitum)



      • Suspect if have cavitated nodules


    • Occasional reports of bronchogenic carcinoma developing in chronic aspiration



      • Suspect if mass enlarging or cavitation


  • Fire-eater’s pneumonia



    • Unique form of lipoid pneumonia due to aspiration of paraffin hydrocarbons used to fuel fire


    • Aspiration results in acute lipoid pneumonia


    • Besides fat attenuation in lung, often develop pneumatoceles


Radiographic Findings



  • Radiography



    • Radiographic appearance nonspecific, either consolidation or interstitial opacities


    • Prominent mass leads to workup for presumptive diagnosis of bronchogenic carcinoma


MR Findings



  • May show fat: High T1 and T2 signal or demonstrate chemical shift on in-out phase T1-weighted imaging



    • Hemorrhage (if acute animal fat ingestion) will also be high at T1- and T2-weighted imaging


Imaging Recommendations



  • Best imaging tool



    • CT is best imaging tool to characterize lesions for presence of fatty component


    • Unknown whether MR more sensitive for fat


Nuclear Medicine Findings



  • PET: Chronic mass lesions often PET positive, mistaken as bronchogenic carcinoma if fat not specifically looked for at CT



DIFFERENTIAL DIAGNOSIS


Other Intrathoracic Lesions Containing Fat

Sep 20, 2016 | Posted by in RESPIRATORY IMAGING | Comments Off on Lipoid Pneumonia
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