Septic Emboli



Septic Emboli


Aqeel A. Chowdhry, MD

Tan-Lucien H. Mohammed, MD, FCCP










Axial CECT shows multiple peripheral thick-walled cavitary nodules image from septic emboli.






Axial CECT coronal reconstruction shows distribution and number of cavitary nodules image.


TERMINOLOGY


Definitions



  • Septic embolism occurs when infected purulent material is dislodged and embolizes to lung


IMAGING FINDINGS


General Features



  • Best diagnostic clue: Multiple nodular opacities rapidly evolving into cavitary nodules


  • Patient position/location: Basilar and peripheral


  • Size: Usually small (< 3 cm diameter)


  • Morphology: Nodules more common than wedge-shaped opacities


CT Findings



  • Morphology



    • Nodules



      • Majority < 3 cm diameter although they can grow much larger


      • Edges indistinct, may have halo sign


      • Air bronchograms seen in 25%


      • Average number 15 per patient


    • Wedge-shaped opacities



      • Peripheral heterogeneous density


      • Edge may enhance with intravenous contrast


      • Average number 6 per patient


    • Cavitation (50%)



      • More common in nodules than wedge-shaped opacities


      • Thickness of cavity wall varies from thick to thin (reflects stages of evolution)


      • Usually no air-fluid level


    • Distribution



      • More common in bases (reflects gravity-dependent blood flow)


      • Bilateral, right lung more nodules than left


      • Peripheral (within 2 cm of pleura) (90%)


    • Feeding vessel sign



      • Vessel leading directly to edge of nodule, found in up to 60-70% of patients


      • MDCT with reconstructions shows that vessel sign usually represents pulmonary veins coursing next to nodule


  • Evolution



    • Rapid cavitation, typically over 24-48 hours



    • Nodules often in various stages of cavitation: No wall to thin wall


    • May change in number or appearance (size or degree of cavitation) from day to day


    • Resolution: May resolve completely with antibiotic therapy, may also result in small residual linear or nodular scars


  • Pulmonary artery



    • Visible embolus extremely uncommon


  • Adenopathy (20%)


  • Pleural effusions (70%)



    • May be bilateral or unilateral


    • Small common; if loculated consider empyema


  • Heart



    • May see valve vegetations, especially with gated studies


  • Indwelling central catheters or pacemaker lead common source



    • Examine closely for adherent clot (may be source of infection)


  • May have infection in other organs seen on chest CT (liver abscess, osteomyelitis, renal abscesses)


Radiographic Findings



  • Radiography: Poorly defined nodular opacities often small and few in number; may be easily missed


Imaging Recommendations



  • Best imaging tool: CT may be abnormal before blood cultures are positive


  • Protocol advice: ECG-gated MDCT may be useful to look for valve vegetations


Echocardiographic Findings



  • Transesophageal echocardiography is procedure of choice to examine valves for vegetations


DIFFERENTIAL DIAGNOSIS


Pulmonary Emboli



  • Visible emboli in pulmonary artery, uncommon with septic emboli


  • With infarcts



    • Infarcts uncommon, usually require some underlying cardiopulmonary disease


    • Pulmonary infarctions rarely cavitate, cavitation common with septic emboli


  • Pleural effusions nearly always present with infarction, also common with septic emboli


Lung Abscess



  • Typically have air-fluid level, less common in septic emboli


  • Evolves more slowly over days and weeks


  • Fewer in number


  • Etiology varies



    • Periodontal disease



      • Gravity-dependent segments: Posterior segments of upper lobe or superior segments of lower lobes


      • Polymicrobial, especially anaerobic organisms like Peptostreptococcus or Fusobacterium


Metastases



  • Cavitation seen with



    • Squamous cell carcinoma, sarcomas, most common cell types


  • Do not rapidly evolve and do not respond to antibiotic therapy


  • Usually more numerous in number


  • Usually variable in size


  • Also have feeding vessel sign


Wegener Granulomatosis



  • Nodules with varying degrees of cavitation


  • Do not rapidly evolve


  • May have subglottic tracheal stenosis


  • Respond to steroid therapy but not to antimicrobial treatment


Rheumatoid Nodules



  • Nodules uncommon manifestation of rheumatoid arthritis (< 5%)


  • Also few in number, typically subpleural


  • Cavitation (50%) thick- or thin-walled


  • Often associated with pneumothorax



  • Usually associated with subcutaneous nodules


Foreign Body Embolus



  • Source: Catheter fragments, vertebroplasty cement, radioactive prostatic seeds


  • Rarely causes nodules or infraction


Tumor Embolism



  • Seen with hepatocellular carcinoma, renal cell carcinoma, or any tumor with extension into venous system


  • Rarely causes infarcts


  • Smaller tumors may grow and expand vessel, mass maintains shape of vessel


  • Intraluminal clot similar to venous embolism


PATHOLOGY


General Features

Sep 20, 2016 | Posted by in RESPIRATORY IMAGING | Comments Off on Septic Emboli
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