Aspiration



Aspiration


Gerald F. Abbott, MD





Key Facts


Terminology



  • Aspiration



    • Intake of solid &/or liquid materials into airways and lungs


  • Aspiration pneumonia



    • Pulmonary infection caused by aspiration of colonized oropharyngeal secretions


  • Aspiration pneumonitis



    • Acute lung injury caused by aspiration of materials inherently toxic to lungs


Imaging Findings



  • Unilateral or bilateral airspace consolidation in gravity-dependent distribution


  • Supine position: Superior segments, lower lobes, & posterior segments of upper lobes


  • Upright position: Basilar segments, lower lobes


  • Even large-quantity aspiration syndromes can be unilateral


  • Endotracheal or tracheostomy tubes do not protect from aspiration


Top Differential Diagnoses



  • Pulmonary Emboli


  • Pulmonary Edema


  • Eosinophilic Pneumonia


Pathology



  • 50% of adults aspirate oropharyngeal secretions during sleep


Clinical Issues



  • Silent aspiration: 50% of anesthetized patients have no symptoms







Axial CECT shows patchy areas of consolidation and centrilobular nodules image that involve the posterior segments of both upper lobes.






Axial CECT shows bilateral diffuse perihilar consolidation that involves the superior and basal segments of both lower lobes, typical locations for aspiration.


TERMINOLOGY


Definitions



  • Aspiration: Intake of solid &/or liquid materials into airways and lungs


  • Aspiration pneumonia: Pulmonary infection caused by aspiration of colonized oropharyngeal secretions


  • Aspiration pneumonitis: Acute lung injury caused by aspiration of materials inherently toxic to lungs



    • Common toxic agents: Gastric acid, milk, mineral oil, volatile hydrocarbons


  • Specific aspiration syndromes



    • Foreign bodies: Most common endobronchial mass in children; food particles (vegetables) and broken fragments of teeth (elderly)



      • Most commonly lodge in main and lobar bronchi


    • Lentil aspiration pneumonia: Granulomatous pneumonitis caused by aspiration of leguminous material (e.g., lentils, beans, peas)


    • Diffuse aspiration bronchiolitis: Recurrent aspiration; typically elderly patients with neurologic disorders, dementia, or oropharyngeal dysphagia



      • Disseminated tree-in-bud opacities with patchy lobular consolidation


    • Mendelson syndrome: Aspiration of sterile gastric contents during labor and delivery; can be severe and fatal


    • Exogenous lipoid pneumonia: Repeated aspiration or inhalation of mineral oil or oily nose drops in adults, cod liver oil and milk in children


    • Near drowning: Pulmonary edema after acute aspiration of massive amounts of fresh or salt water



      • Secondary pneumonia may occur depending on composition of aspirate


    • Hydrocarbon pneumonia: Accidental, suicidal, or occupational poisoning with variety of toxic substances



      • Children: Furniture polish


      • Hydrocarbon containing fluid: Petroleum-based fluids


      • Flame swallowers (known as fire-eater’s pneumonia)



IMAGING FINDINGS


General Features



  • Best diagnostic clue



    • Gravity-dependent opacities


    • Radiopaque material in airway lumen (solid &/or liquid material; foreign body)


  • Patient position/location



    • Aspiration syndromes typically in gravity-dependent locations



      • Supine position: Superior segments of lower lobes & posterior segments of upper lobes


      • Upright position: Basilar segments, lower lobes


      • Right hemithorax more common than left (due to vertical orientation of right-sided central airways)


CT Findings



  • Foreign bodies



    • Direct visualization of foreign bodies but may be overlooked


    • Distal atelectasis of lobe of lung or focal airspace consolidation should be traced back to supplying airways


  • Aspiration pneumonia and pneumonitis



    • Variable patterns that depend on quantity and quality of aspirate



      • Tree-in-bud opacities seen with aspirated material in small airways, characteristic finding in lentil aspiration


      • Consolidation from aspirate into airspaces; may evolve into adult respiratory distress syndrome (ARDS) or pneumonia


      • Bronchiectasis from injury to major airways, usually seen with chronic recurrent aspiration; can be acute depending on toxicity of aspirate


      • Interstitial fibrosis from airspace injury


    • Lipoid pneumonia: Low attenuation (fat density) in focal consolidation, may also have “crazy-paving” pattern


    • Hydrocarbon pneumonia: Often develop pneumatoceles in areas of consolidated lung


    • Near drowning: “Sand bronchogram” (radiopaque) if sand (coral) aspirated along with water


    • Granulomatous pneumonitis (lentil aspiration)



      • Centrilobular ill-defined nodules (foreign body granulomas)


      • Tree-in-bud opacities


Radiographic Findings



  • Foreign body



    • Atelectasis: Lung, lobar, or segmental depending on size of foreign body


    • Hyperinflation & air-trapping more common in children


  • Aspiration pneumonia and pneumonitis



    • Unilateral or bilateral airspace consolidation in gravity-dependent distribution



      • Supine position: Superior segments of lower lobes and posterior segments of upper lobes


      • Upright position: Basal segments of lower lobes, right more than left


      • Decubitus position: Axillary subsegments of upper lobes


      • Recurrent aspiration often favors same location due to anatomic drainage patterns in individual patient


      • Even large quantity aspiration syndromes can be unilateral


    • Diffuse perihilar consolidation more common with pneumonitis


    • Endotracheal or tracheostomy tubes do not protect from aspiration



      • Fluid may accumulate above endotracheal balloon, source of aspiration pneumonia


    • Acute aspiration pneumonitis may quickly evolve into ARDS


    • Untreated aspiration pneumonia often leads to necrotizing pneumonia and lung abscess


    • Chronic aspiration syndromes from retained foreign bodies or recurrent aspiration pneumonia (pneumonitis) may lead to bronchiectasis


    • Recurrent: Multiple episodes, sometimes identical in appearance, may wax and wane over time



    • Resolution variable, depends on quantity and type of aspirate; nontoxic aspirate will clear within hours


Imaging Recommendations



  • Best imaging tool: CT more sensitive for airspace and airway abnormalities


  • Protocol advice



    • Maximum intensity projection (MIP) images may optimize visualization of centrilobular nodules and tree-in-bud opacities


    • In infants, lateral decubitus radiographs to investigate air-trapping


    • Esophagrams may be useful to study motility and structural abnormalities


DIFFERENTIAL DIAGNOSIS


Acute Aspiration



  • Pulmonary emboli



    • Common cause of acute respiratory distress in hospitalized patients


    • Infarcts often peripheral and associated with pleural effusion


  • Pulmonary edema



    • Cardiomegaly, often with bilateral pleural effusions


    • Kerley B lines uncommon with aspiration


  • Adult respiratory distress syndrome



    • Identical radiographic findings


Chronic Aspiration



  • Endobronchial obstruction



    • Slow-growing endobronchial tumors such as carcinoid or chronic obstructing lesions such as broncholithiasis


  • Bronchiectasis and tree-in-bud opacities



    • Mycobacterial opportunistic infections



      • Typically in elderly women with chronic cough


      • Bronchiectasis typically middle lobe and lingula, uncommon areas for aspiration

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

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