Airways

The entire respiratory tree is lined by pseudostratified columnar ciliated epithelial cells. Bronchial mucosa also has neuroendocrine cells capable of secreting serotonin, calcitonin, gastrin-releasing peptide. Goblet cells and submucosal glands in the trachea and bronchi (not bronchioles) secrete mucous.

Trachea and Central Bronchi

Congenital Anomalies

  • Tracheocoeles (paratracheal air cysts) – True diverticulum through weak posterior tracheal membrane, almost exclusively in cervical trachea (pressure gradient). Usually asymptomatic.
  • Tracheal bronchus (bronchus suis) – Accessory bronchus in 0.5-1% from right lateral tracheal wall within 20mm of carina, suppying all or partion RUL (most commonly apical segment). Associated with congenital tracheal stenosis and aberrant LPA. Most asymptomatic.

Stenosis/Narrowing

Focal tracheal or central bronchial (main or lobar) stenosis:

  • Extrinsic compression/narrowing – From goiter, enlarged LN, tortuous/aneurysmal aortic arch, congenital vascular anomaly, large bronchogenic cyst. Tend to displace rather than narrow due to resilient tracheal cartilage. Deformity also seen in apical scarring (TB, histoplasmosis).
  • Post-instrumentation – Cartilaginous damage or granulation tissue and fibrosis from previous tracheostomy or endotracheal tube (rare with current low-pressure balloons). Stenosis is typically hourglass shape. Tracheomalacia with narrowing during certain phases of respiration (extrathoracic during inspiration, intrathoracic during expiration).
  • Wegener granulomatosis – Necrotising granulomatous inflammation in trachea/central bronchi, may be entire length in advanced disease.
  • Sarcoidosis (rare)
  • Infection – Endo-tracheal/bronchial TB, esp with cavitatory TB where there is large volumes of infected sputum. Histoplasmosis and coccidioidomycosis. Invasive tracheobronchitis from aspergillosis, candidiasis, mucormycosis in immunodeficiency.
  • Tracheal scleroma – Chronic granulomatous inflammation by Klebsiella rhinoscleomatis infection, starting with inflammed nasal mucosa and paranasal sinuses extending inferiorly; irregular nodular narrowing, may involve entire length of trachea.
  • Neoplasm – Primary malignant SCC, adenoid cystic carcinoma (cylindroma). Metastatic laryngeal, thyroid, oesophageal, bronchogenic, breast, RCC, colon, melanoma. Benign chondroma, fibroma, squamous cell papilloma, haemangioma, granular cell myoblastoma.
  • Ectopic thyroid or thymus
  • Mucous

Diffuse tracheal narrowing:

  • Saber-sheath trachea – Fixed intrathoracic coronal diameter < 2/3 sagittal diameter. Tracheal wall uniformly thickened, most have calcification in cartilaginous rings. Exclusively older men with COPD, likely from chronic transmission of increased intrapleural pressure and injury from chronic cough.
  • Amyloidosis – Masslike circumferential submucosal deposits, irregularly narrowing the lumen. May cause recurrent atelectasis and pneumonia. Calcification in 10%.
  • Tracheobronchopathia osteochondroplastica – Rare, elderly men. Multiple enchondromas from tracheal and bronchial cartilage projecting internally, creating submucosal osseous and cartilaginous deposits. Sparing of membranous posterior wall (lacks cartilage). May be asymptomatic or cause recurrent infections.
  • Relapsing polychondritis – Systemic autoimmune disease affecting cartilage of earlobes (cauliflower ears), nose (saddlenose deformity), larynx, trachobronchial tree, joints, large elastic arteries. Inflammation and cartilage destruction initially causes dilated trachea, later fibrosis leads to diffuse fixed narrowing. 2 or more cartilaginous sites of involvement
  • Wegener granulomatosis
  • Tracheal scleroma

Dilatation

Focal tracheal dilatation is congenital or acquired abnormality of elastic membrane or cartilaginous rings.

  • Tracheocoeles
  • Acquired tracheomalacia from prolonged intubation
  • Traction from severe upper lobe scarring

Diffuse tracheal dilatation:

  • Tracheobronchomegaly (Mounier-Kuhn syndrome) – Congenital disorder of elastic and smooth muscle of trachea, associated with Ehlers-Danlos (collagen synthesis) and cutis laxa (elastic tissue). Almost exlcusively males <50yo. Abnormal compliance causes collapse with cough. Impaired mucociliary clearance predisposing to recurrent pneumonia, bronchiectasis. Trachea and central bronchi >25mm, corrugated appearance (herniation of mucosa and submucosa between cartilages), hyperinflated lungs +/- bullae.
  • Tracheobronchomalacia – Congenital or acquired defect of tracheal cartilage, most commonly COPD, chronic bronchitis, CF, relapsing polychondritis. Findings similar to tracheobronchomegaly.
  • Long-standing interstitial pulmonary fibrosis – ?Longstanding elevation in transpulmonary pressures from reduced lung compliance or chronic cough.

Trauma

Most tracheobronchial injury from blunt trauma in deceleration-type injury, with forceful compression against thoracic spine. Almost all associated with great vessel injury, rib fracture (most upper anterior), sternal, scapular or vertebral fracture. Fractures in proximal main bronchi (80%) or distal trachea within 20mm of carina (15%), most transected parallel to cartilage. Pneumothorax and pneumomediastinum, failing to respond to chest drain (large air leak). Subtended lung remains collapsed against lateral chest wall (‘fallen lung’). Aberrant endotracheal tube or overdistended balloon cuff. 1/3 have delayed diagnosis, these may present with collapsed lung, pneumonia or bronchial stenosis. Definitive diagnosis by bronchoscopy.

Penetrating tracheal injuries usually cervical trachea from gunshot or stab to neck, usually with fatal cardiovascular injury.

Broncholithiasis

Calcifid material within the tracheobronchial tree, from erosion of calcified peribronchial lymph node into the lumen. Most from granulomatous inflammation (histoplasmosis, TB). May occlude airway causing bronchiectasis, atelectasis or pneumonia. Often asymptomatic, may have lithoptysis (productive cough of stones), haemoptysis (erosion into bronchial vessel).

Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) – Damage to acini (emphysema) and bronchi (bronchitis) in addition to small airways (bronchiolitis). Some have a reversible element; some patients with asthma also have an irreversible element hence may be labelled as COPD/asthma. Most have history of smoking, 10% are nonsmokers. Only a minority of smokes develop COPD of unknown reason. Predominant bronchitis (blue bloater) occurs 40-45yo with mild late dyspnoea, early productive cough. Predominant emphysema (pink puffer) occurs 50-75yo, early severe dyspnoea, late cough.

Chronic Bronchitis

(‘Increased markings emphysema’, ‘blue bloaters’, chronic hypoxaemia with polycythaemia). Clinical diagnosis, excessive production and expectoration of sputum on most days for at least 3/12 in at least 2 consecutive years. Increased risk with smoking (90% are smokers), smog-laden cities, dust from grain/cotton/silica. Hypertrophy of submucosal glands in trachea and bronchi, increased goblet cells in small bronchi/bronchioles, with hypersecretion of mucous, worst in lower lobe bronchi with wall thickening. High Reid index >0.5(submucosal mucous gland thickness to bronchial wall thickness from epithelium to cartilage). 50% have normal CXRs, some show peribronchial cuffing or tram-tracking, ‘dirty chest’ with accentuated peripheral lung markings (?small airways disease or prominent pulmnary aa from PAH). Bronchiole narowing from mucus plugging, inflammation, fibrosis (bronchiolitis obliterans). When persistant may cause recurrent infections, COPD, cor pulmonale, atypical squamous metaplasia/dysplasia with malignant transformation.

Emphysema

Permanently enlarged airspaces distal to terminal bronchioles with destruction of alveolar walls without obvious fibrosis. Increased risk with smoking, African Americans. Smoking causes accumulation of neutrophils with proteases (eg elastase) and antiprotease inhibitors destroying alveolar septa (protease-antiprotease imbalance). Oxidative injury inactivates native antiproteases causing ‘functional’ alpha-1-antitrypsin deficiency. Loss of elastin and elastic recoil reduces radial traction, with collapse of respiratory bronchioles during expiration, leading to functional airflow obstruction. Inflammation and small airways obstruction causes distention, predominantly centrilobular, may contribute to panlobular emphysema. Reduced airflow and diffusing capacity (DLCO) due to reduced surface area, airflow obstruction (low FEV1) from raised airways resistance and decreased outflow driving pressure (elastic recoil). Radiographic findings may not correlate with degree of airflow obstruction (ie have emphysema but may not have clinical COPD). Clinical manifestation does not usually appear until >1/3 of functional parenchyma is damaged.

  • Centrilobular/centriacinar emphysema (95%) – Spares periphery of the lobule, upper > lower lobes. Initial dilatation of respiratory bronchioles. Associated with smoking and chronic bronchitis.
  • Panlobular/panacinar emphysema – More uniform through the lobule, lower > upper lobes. Initial distension of alveoli and alveolar ducts. Associated with alpha-1-antitrypsin deficiency.
  • Paraseptal (distal acinar) emphysema – Adjacent to interlobular septa with central sparing, esp subpleural upper lobes; may coalesce to form apical bullae. Occurs adjacetnt to fibrosis, scarring or atelectasis.
  • Paracicatricial/irregular emphysema (airspace enlargement with fibrosis) – Associated with fibrosis with no relationship within lobule, most associated with old granulomatous inflammation.

Hyperinflation (loss of elastic recoil) with inferior displacement and flattening of diaphragms, obtuse/right angles of constophrenic sulci, increased AP diameter (barrel chest), increased retrosternal clear space. Absent/attenuated peripheral vascular markings with diffuse hyperlucency from parenchymal destruction and hyperinflation. Thin-walled bullae (panlobular > centrilobular). Increased peripheral arterial resistence from chronic hypoxaemia causes PAH with enlarged central PAs, right heart enlargement. ‘Arterial deficiency emphysema’ (‘pink puffers’ with tachypnoea and normal O2) – predominant emphysema with peripheral vascular attenuation, normal heart/PAs, bullae common. On CT the dilated airspaces lack definable walls.

Bullae are thin-walled cystic spaces >10mm. Type 1 are apical, subpleural, narrow neck, rounded without septations; type 2 subpleural with wide neck, strands of residual tissue; type 3 deep within lung with wide neck, strands ot tissue. Most represent confluent emphysema. May also be seen with chronically elevated transpleural pressure gradient and increased lung weight in interstitial fibrosis, disease causing chronic upper lobe fibrosis and bronchiolar obstruction hence distention and septal disruption (sarcoidosis, LCH, ankylosing spondylitis). Primary bullous disease may be familial, associated with Marfan syndrome, Ehlers-Danlos syndrome, IVDU, HIV, vanishing lung syndrome (accelerated upper lobe paraseptal emphysema in young men, asymptomatic unless causes compression, rounded bullae of varying sizes). Rupture leads to pneumothorax, with persistent air leak difficult to treat. Infection leads to air-fluid level resolving over several weeks with ABs. Cancer may rarely form in wall. Bullectomy if symptomatic or enlarging.

Other forms of emphysema:

  • Alpha-1-antitrypsin (protease inhibitor) deficiency – 1% of patients with emphysema. AR mutation in proteinase inhibitor (PI) gene on chromosome 14. Normal is M alele, disease from Z allele. Panlobular emphysema by middle age if homozygous (ZZ), slight increased risk if heterozygous (MZ), accelerated with smoking.
  • Compensatory hyperinflation/emphysema – Dilation of alveoli without destruction of septal walls, from loss of parenchyma elsewhere.
  • Obstructive overinflation – Incomplete bronchial obstruction with ball-valve effect or complete obstruction with collateral flow via pores of Kohn and canals of Lambert. May compress remaining normal lung.
  • Bullous emphysema – Large subpleural blebs or bullae, usually near apices.
  • Interstitial emphysema – Air in interstitium, from alveolar tears in emphysema, trauma, coughing, ventilation, noxous gases.

Asthma

Reversible bronchial smooth muscle contraction, bronchial wall inflammation and excessive mucus production. Attacks may be triggered by infection (esp viral), environmental irritants (smoke, fumes), cold air, stress, exercise. Status asthamticus – unremitting attacks with bronchospasm, may be fatal. Hyperinflation, flattening/inversion of diaphragm, attenuation of peripheral vascular markings, peribronchial cuffing and ‘tram-traking’, prominent hila (transient PAH from hypoxic vasoconstriction). Airway remodelling includes wall thickening, sub-basement membrane fibrosis, increased vascularity, hyperplasia of submucosal glands, epithelial metaplasia, hypertrophy/hyperplasia of bronchial wall muscle. Mucous plugs (whorls of shed epithelium in Curschmann spirals, eosinophils, Charcot-Leyden crystals) may cause osbtruction and atelectasis, pneumonia. Expiratory obstruction may cause alveolar rupture, dissection of air medially to cause pneumomediastinum or peripherally to form subpleural blebs, pneumothorax.

  • Atopic asthma (most common) – IgE mediated, usually beginning in childhood. Triggered by dust, pollens, roach/animal dander, foods. Often associated with FHx, allergic rhinitis, eczema.
  • Non-atopic asthma – Triggers (viruses esp rhinovirus, parainfluenza virus; air polutants eg sulfur dioxide, ozone, nitrogen dioxide) induce inflammation of mucosa, lowering threshold of vagal receptors. Less commonly has FHx, skin allergen tests usually negative.
  • Drug-induced asthma – Aspirin/NSAID-sensitive asthma is uncommon, associated with recurrent rhinitis and nasal polyps.
  • Occupational asthma – Fumes (epoxy resins, plastics), organic and chemical dusts (wood, cotton, platinum), gases (toluene) or other chemicals (formaldehyde, penicillin products) induce hypersensitivity reactions.

Bronchiectasis

Abnormal permanent dilatation of bronchi and bronchioles with destruction of muscle and elastic tissue. Chronic sputum production and recurrent LRTIs, haemoptysis with enlarged bronchial aa common. Multiple disorders, all cause chronic inflammation to bronchi with tissue destruction. Mixed flora of staphylococci, streptococci, pneumococci, enteric organisms, H.influenze, Pseudomonas.

  • Localised bronchiectasis (most peripheral) – From TB, extrinsic compression of bronchi, bronchial stenosis/occlusion (bronchial atresia, TB, sarcoid, previous injury), endobronchial mass (carcinoid, bronchogenic carcinoma) or foreign body.
  • Diffuse bronchiectasis – From CF, dysmotile cilia syndrome, congenital immunodeficiency, postinfectious including bacteria (TB, MAI, S.aureus, H.influenze, pseudomonas) and viral (adenovirus/Swyer-James syndrome, measles, pertussis), chronic aspiration, ABPA, traction bronchiectasis (IPF, TB).
  • Central only – From ABPA, CF, bronchial atresia or acquired central bronchial obstruction.

Cylindric (mild diffuse dilatation), varicose (cystic dilatation with focal areas of narrowing, ‘string of pearls’), or saccular/cystic (cluster of marked saccular dilatations). Scarring, volume loss, ill-defined bronchovascular markings, parallel linear shadows, multiple peripheral thin-walled cysts +/- air-fluid levels around bronchovascular bundle (cystic), bronchial wall thickening. Bronchi > diameter with accompanying PAs (signet ring’), airways visible peripherally almost to pleural surface. Mucoid impaction within dilated bronchi mimic nodules, branching ‘finger-in-glove’ opacities. Fibrosis of bronchial and bronchiolar walls may lead to bronchiolitis obliterans.

  • [[Paediatric_Chest#Cystic Fibrosis (CF)|Cystic Fibrosis (CF)]] – Hereditary, young Caucasions with abnormal thick tenacious mucus. Sweat test shows abnormal high chloride. Mucous plugs in small airways causes obstruction and infection; recurrent infection (Pseudomonas aeruginosa, Staphylococcus aureus) leads to bronchiectasis, functional airways obstruction. Haemoptysis may be massive, requiring embolisation. Hyperinflation, predominantly upper lobe bronchiectasis and mucus plugging, distal atelectasis and obstructive pneumonitis, prominent LN from infection, PAH. Smaller bronchioles are progressively obliterated from fibrosis (bronchiolitis obliterans). Poor prognosis with mortality in early adulthood.
  • Dysmotile cilia syndrome (primary ciliary dyskinesia) – AR, abnormal ineffective epithelial cilial motion. Kartagener syndrome in 1/2 with triad of chronic sinusitis, situs inversus (impaired cell motility during embryogenesis) and bronchiectasis. May also have dysmotile spermatozoa and sterility. Diffuse bronchiectasis, hyperinflation.
  • Postinfectious bronchiectasis – Severe childhood pneumonia (adenovirus, measles, pertusus) may cause bronchial damage, recurrent infection and bronchiectasis. In some, bronchiolitis obliterans may lead to an underdeveloped lung (Swyer-James syndrome).
  • Allergic bronchopulmonary aspergillosis (ABPA) – Hypersensitivity to Aspergillus fumigatus. May be a complication of asthma and cystic fibrosis. Blood eosinophilia, bronchiectasis with mucus plugging, serum antibodies to Aspergillus. Type 1 hypersensitivity causes acute wheeze, dyspneoa; type 3 causes bronchial wall inflammation and proximal predominantly upper lobe bronchiectasis. Dilated air-filled tubules or branching opacities (mucoud impaction). Tx corticosteroids.
  • Bronchial obstruction – Endobronchial obstruction from neoplasm, atresia, stenosis may cause downstream bronchiectasis. Mucus plugging (mucocoeles) may be seen if there is adequate collateral ventilation to adjacent lung without collapse in slow-growing lesions (eg carcinoid).

Bronchiolitis

Inflammation of small noncartilaginous airways. Direct signs include centrilobular GGO, sharply defined opacity or Y/V- shaped tree-in-bud brancing opacities, within 10mm of pleural surface; representing dilatation and mucus plugging. Indirect signs include mosaic attenuation with expiratory air-trapping (DDx reduced perfusion in PE with reduced calibre of affected vessels; infiltrative patchy GGO in PCP, DIP). Types include:

  • Infectious bronchiolitis – Young children from RSV or adenovirus; in adults from viral/atypical/mycobacterial infections. Hyperinflation, tree-in-bud, indistinguishable from asthma.
  • Respiratory bronchiolitis-associated interstitial lung disease (RB-ILD) – Centrilobular and geographic GGO. Associated with smoking.
  • Subacute hypersensitivity pneumonitis – Centrilobular GGO, air trapping on expiration
  • Follicular bronchiolitis – Diffuse hyperplasia of peribronchiolar lymphoid follicles associated with RA or Sjogren syndrome of unknown significance. Ill-defined centrilobular ground-glass nodules, occasionally bronchial dilatation.
  • Constrictive bronchiolitis (bronchiolitis obliterans) – Subacute mononuclear inflammation of respiratory bornchiolar walls with granulation tissue causing plugging. May be idiopathic or secondary to organ transplant (esp lung, heart-lung and bone marrow), virus, toxic fume inhalation, drug reaction, collagen vascular disease, chronic aspiration. Diffuse reticulonodular, hyperinflation, central bronchiectasis, mosaic attenuation with air trapping on expiration.

*

  • Swyer-James syndrome (unilateral hyperlucent lung) – Early childhood adenovirus LRTI with asymmetrical diffuse small airways obliteration. Air trapping with collateral air drift to distal airspaces limiting excape and hence markedly delayed radiotracer washout, destruction of alveolar walls, emphysema. Later lung becomes small as there is limited growth and development with associated hypoplastic PA. Most are asymptomatic, some SOB or recurrent LRTI.
  • Diffuse/Asian panbronchiolitis – Uncommon, progressive symptoms associated with sinus disease. Diffuse tree-in bud, central bronchiectasis.