(aka Unilateral Hyperlucent Lung, Unilateral Emphysema)
Epidemiology
- Rare condition (one case every 2-4 years on busy pulmonary service)
Etiology (one of the first 4 is present in 50% of cases):
1) Childhood Measles:
2) Childhood or Adulthood Viral URI (especially Adenovirus and RSV):
3) Mycoplasma URI:
4) Primary Pulmonary TB (uncommon etiology):
5) Toxic Fume Exposure:
6) Pneumococci:
Physiology
-Early Life Bronchiolitis Prior to Age 8 (particularly viral, due to adneovirus or RSV) -> impaired development of peripheral airways -> decreased lung perfusion on the affected side
-Unilateral bronchiolitis obliterans with lung hyperinflation (and sometimes bronchiectasis)
-Increased pulmonary vascular resistance in the affected lung (due to increased intraalveolar mean pressure distal to obliterated narrowed bronchi and bronchioles)
-Some alveoli remain aerated due to collateral drift (creating patchy distribution of pigment on lung surface grossly in urban dwellers)
-Airspace enlargement may occur due to failure of increase in alveolar number after age 8 (with distention as the thorax grows)
Pathology
- Normal-small lung (that remains inflated when chest is opened) with patchy bronchiolitis obliterans and bronchitis
- normal bifurcations of bronchial tree
- panacinar emphysema
- lack of large air spaces (usually)
- thickening of pulmonary artery walls and some decrease in number of branches
Diagnosis
ABG: absence of rest/exercise hypoxemia
PFT’s: minimal-mild obstruction (with increased RV)
-Increased RV/TLC ratio: gas trapping
V/Q: decreased ventilation and perfusion to affected lung (may be similar to that seen in endobronchial obstruction)
-Normal equilibrium of ventilation but severely delayed washout
Pulmonary Angiogram: main PA is small with decreased vascular filling of affected lung
CXR: unilateral hyperlucent lung (which is normal-small in size)
-Decreased pulmonary vasculature
Chest CT: may reveal bronchiectasis on affected side
-Inspiratory/expiratory CT may be useful to demonstrate focal gas trapping
Fluoro: impaired emptying of affected lung (with shift of mediastinum to opposite side) during expiration
Bronchograms: poor peripheral filling of airways/bronchiectasis may be seen
Clinical
Symptoms/Signs (usually asymptomatic):
1) Decreased BS on Affected Side:
2) Decreased Hemithorax Size:
2) Symptoms/Signs of Bronchiectasis: sputum production, coarse crackles
-Exertional dyspnea is uncommon
-Respiratory failure is uncommon
Treatment
Treatment of Respiratory Infections:
Surgical Resection: may be indicated for recurrent infection or bleeding in bronchiectatic area
Avoid Smoking: to prevent further gas trapping
Avoid Scuba Diving: due to risk of barotrauma
Prognosis
- Excellent
References
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