000 Bronchiolitis

Etymology

  • Derived from the Greek words bronchion, meaning “small airway,” and -itis, meaning “inflammation.” The term refers to inflammation of the bronchioles.

AKA

  • Small airway inflammation

What is it?

  • Bronchiolitis is a clinical and radiological condition characterized by inflammation and injury to the bronchioles, the smallest airways in the lungs, leading to airway narrowing, obstruction, and impaired gas exchange.

Caused by:

  • Most common causes:
    • Viral infections (e.g., respiratory syncytial virus [RSV] in children)
    • Post-infectious inflammatory response
  • Less common causes:
    • Infection:
      • Mycoplasma pneumoniae
      • Influenza virus
    • Inflammation:
      • Chronic inhalation of irritants (e.g., smoke, fumes)
      • Hypersensitivity pneumonitis
    • Immune:
      • Rheumatoid arthritis-associated bronchiolitis
      • Connective tissue diseases
    • Neoplasm:
      • Bronchiolar obstruction due to tumors
    • Mechanical:
      • Aspiration of foreign material
    • Inflammation:
      • Chronic bronchitis
      • Connective tissue diseases (e.g., rheumatoid arthritis)
      • Radiation-induced bronchiolitis
    • Inherited and Congenital:
      • Primary ciliary dyskinesia
      • Alpha-1 antitrypsin deficiency
    • Other:
      • Drug-induced bronchiolitis (e.g., chemotherapy agents, amiodarone)

Resulting in:

  • Airway narrowing and obstruction
  • Impaired mucociliary clearance
  • Reduced gas exchange efficiency

Structural Changes:

  • Bronchiolar wall thickening
  • Peribronchiolar inflammation
  • Mucus plugging and potential fibrosis in chronic cases

Pathophysiology:

  • Bronchiolitis develops when the bronchiolar epithelium is injured due to infection, inflammation, or other insults. This injury triggers an inflammatory response, leading to swelling of the bronchiolar walls, mucus production, and sometimes fibrosis. Air trapping and ventilation-perfusion mismatch may result, causing symptoms such as dyspnea and hypoxemia.

Pathology:

  • Inflammatory infiltrates in and around bronchioles
  • Mucus and cellular debris obstructing the lumen
  • Fibrosis in chronic or recurrent cases

Diagnosis

Clinical:

  • Symptoms vary based on etiology:
    • Acute: Cough, wheezing, dyspnea, and fever
    • Chronic: Persistent cough, dyspnea, and exercise intolerance
  • Examination findings:
    • Wheezing or crackles on auscultation
    • Signs of hypoxemia in severe cases

Radiology:

  • CXR:
    • Hyperinflation, particularly in acute viral bronchiolitis
    • Patchy areas of consolidation or atelectasis
  • CT of the Chest:
    • Tree-in-bud opacities in infectious or inflammatory bronchiolitis
    • Mosaic attenuation indicating air trapping
    • Bronchiolar wall thickening

Labs:

  • Viral testing (e.g., RSV antigen)
  • Sputum cultures for bacterial or fungal infections
  • Autoimmune panels for connective tissue disease-associated bronchiolitis

Management:

  • Acute bronchiolitis:
    • Supportive care:
      • Oxygen therapy for hypoxemia
      • Hydration and fever management
    • Antiviral or antibiotic therapy if indicated
  • Chronic bronchiolitis:
    • Address underlying cause (e.g., corticosteroids for autoimmune diseases)
    • Bronchodilators for airway obstruction
    • Smoking cessation and avoidance of irritants
    • Immunizations (e.g., influenza, pneumococcal vaccines) for prevention

Radiology Detail

CXR

Findings:
  • Hyperinflation and peribronchial cuffing
  • Subtle patchy opacities in severe cases
Associated Findings:
  • Atelectasis or small airway collapse

CT of the Chest

  • High-resolution CT of the chest with inspiration and expiration can be used when small airway obstruction is suspected or for clarification of mosaic attenuation identified on conventional CT.
Parts:
  • Terminal and respiratory bronchioles
Size:
  • Bronchiolar walls appear thickened
Shape:
  • Tree-in-bud opacities representing impacted bronchioles
Position:
  • Distributed in the central or peripheral lung zones depending on etiology
Character:
  • Irregular, nodular, or beaded bronchiolar patterns
Time:
  • Acute or chronic, depending on the underlying cause
Associated Findings:
  • Air trapping and mosaic attenuation in expiratory images

Other relevant Imaging Modalities

MRI/PET CT/NM/US/Angio:
  • MRI: Rarely used but may assess associated soft tissue abnormalities
  • PET-CT: Useful in identifying active inflammation or malignancy in atypical cases

Pulmonary Function Tests (PFTs):

  • Obstructive pattern with decreased FEV1/FVC ratio
  • Air trapping and reduced diffusion capacity in severe cases

Recommendations:

  • CT of the Chest for detailed evaluation of bronchiolar changes
  • Viral or autoimmune testing based on clinical suspicion
  • Early intervention to prevent progression to chronic disease

Key Points and Pearls:

  • Bronchiolitis refers to inflammation of the bronchioles and can present acutely (e.g., viral infections) or chronically (e.g., connective tissue diseases).
  • CT of the Chest is the gold standard for identifying small airway changes, including tree-in-bud opacities and mosaic attenuation.
  • Management includes supportive care, targeted therapy for underlying causes, and prevention through immunizations and avoidance of irritants.
  • Types

Mosaic attenuation pattern. CT scan through lower lobes shows the indirect sign of constrictive obliterative bronchiolitis, in this case the sequel to a severe viral lower respiratory tract infection.
https://pubs.rsna.org/doi/full/10.1148/radiol.13120908

Tree-in-bud pattern. CT scan through lower lobes shows the direct sign of exudative bronchiolitis in a 42-year-old man with a sino-bronchial sepsis syndrome.
https://pubs.rsna.org/doi/full/10.1148/radiol.13120908
Typical example of high-resolution computed tomography (HRCT) findings in desquamative interstitial pneumonia (DIP). Coronal a) and axial b) computed tomography (CT) slices show bilateral basal and peripheral ground-glass opacity. Some superimposed fine linear opacities are also seen, especially on the left side (coronal slice a)), corresponding with thickened inter- and intralobular septa.
Hellemons M etal Eur Respir Rev 2020; 29: 190181. – September 30, 2020

Progression of DIP and pulmonary fibrosis in a 55-year-old male smoker. (A) Axial CT image through the lower lobes from 2012 shows lower lobe predominant ground glass opacity with scattered cystic changes. In addition, there is mild reticulation (black arrows) and bronchiectasis (white arrows), signifying underlying fibrosis. Open lung biopsy showed DIP and a NSIP of fibrosis. (B) Axial CT image from 2015 at the same level as the scan obtained in 2013 shows progressive fibrosis with worsening reticulation (black arrows) and bronchiectasis (white arrows). Explant showed DIP combined with severely fibrotic NSIP.
Kligerman S et al Clinical-Radiologic-Pathologic Correlation of Smoking-Related Diffuse Parenchymal Lung Disease 2016
  • hypersensitivity pneumonitis (HP)

  • Head cheese or brawn is a cold cut terrine or meat jelly, often made with flesh from the head of a calf or pig (less commonly a sheep or cow), typically set in aspic, that originated in Europe. Usually eaten cold, at room temperature, or in a sandwich, the dish is, despite the name, not a dairy cheese. The parts of the head used in the dish vary, though commonly do not include the brain, eyes or ears of the animal. The tongue, and sometimes the feet and heart of the animal may be included; the dish is also made using trimmings from more commonly eaten cuts of pork and veal, with the addition of gelatin as a binding agent. Head cheese may also be made without using the flesh from the head of an animal.
    Courtesy Rainer Zenz source Wiki

  • Hypersensitivity Pneumonitis
    High-resolution CT: increase in density in areas of ground glass and air trapping in lower lobes in patients with hypersensitivity pneumonitis
    Courtesy Mluisamtz11

Links and References

Ryu, J Pulmonary Medicine Bronchiolitis Pulmonology Advisor

Winningham P, J. et al   Bronchiolitis: A Practical Approach for the General Radiologist RadioGraphicsVol. 37, No. 3 2017

 

Links and References

TCV

Small Airway Disease Introduction

Fleischner Society

bronchiolitis

Pathology.—Bronchiolitis is bronchiolar inflammation of various causes (,33).

CT scans.—This direct sign of bronchiolar inflammation (eg, infectious cause) is most often seen as the tree-in-bud pattern, centrilobular nodules, and bronchiolar wall thickening on CT scans. (See also small-airways disease, tree-in-bud pattern.)