Bilateral Hyperlucent Hemithorax

Dharshan Vummidi, MD

Jeffrey P. Kanne, MD

DIFFERENTIAL DIAGNOSIS

Common

Centrilobular Emphysema
Panlobular Emphysema
Bronchiectasis
Bronchiolitis

Less Common

Constrictive Bronchiolitis
Asthma
Pulmonary Langerhans Cell Histiocytosis
Lymphangiomyomatosis

Rare but Important

Pulmonary Atresia

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Pulmonary causes
- Usually related to airways disease
- Pulmonary vascular causes much less common
Extrapulmonary causes
- Congenital or developmental lack of chest wall soft tissue
- Bilateral mastectomy
Technical
- Overexposure
  - Uncommon with digital radiography
- Incorrect window and level settings on CT

Helpful Clues for Common Diagnoses

Centrilobular Emphysema
- Most common type of emphysema
- Almost always smoking related
- Predominates in upper lobes and superior segments of lower lobes
- Radiography: Hyperinflation, attenuation of vessels in affected areas
- CT: Centrilobular foci of low attenuation without perceptible walls
- Bulla: Emphysematous space > 1 cm
Panlobular Emphysema
- Most commonly associated with α-1-antitrypsin deficiency
- Rarely associated with intravenous drug abuse (e.g., methylphenidate [Ritalin])
- Predominates in basal portions of lungs
- Radiography
  - Hyperinflation
  - Attenuation of vessels in affected areas, particularly lower lung zones
- CT
  - Hyperinflation, particularly of lower lobes
  - Diffusely decreased attenuation of affected lung parenchyma with small vessels
Bronchiectasis
- Hyperinflation and air-trapping from associated small airways disease
- Related to chronic or recurrent infection
  - Rarely result of congenital cartilage abnormality (Williams-Campbell syndrome)
- Radiography
  - Pulmonary hyperinflation
  - Dilated bronchi
  - “Tram-tracking”: Parallel lines representing nontapering walls of ectatic bronchi seen in profile
  - Mucoid impaction may be present
- CT
  - Bronchial abnormalities clearly shown
  - Diffuse low attenuation and small vessels often present in parenchyma supplied by dilated and inflamed bronchi
  - Extensive air-trapping may be apparent on expiratory CT
Bronchiolitis
- Usually infectious
  - Viral
  - Mycoplasma
- Radiography: Hyperinflation, small lung nodules
- CT: Centrilobular nodules, tree in bud opacities

Helpful Clues for Less Common Diagnoses

Constrictive Bronchiolitis
- Submucosal and peribronchial fibrosis resulting in luminal narrowing or occlusion
- Numerous causes
  - Infection: Viral (adenovirus and respiratory syncytial virus), Mycoplasma, Pneumocystis
  - Connective tissue diseases, especially rheumatoid arthritis and Sjögren syndrome
  - Drug reaction
  - Inhalational injury (toxic fumes, smoke)
  - Transplant: Lung and blood stem cell
- Radiography: Normal lung volume to hyperinflation
- CT: Heterogeneity of lung with smaller vessels in areas of low attenuation
  - Expiratory imaging confirms presence of air-trapping
Asthma
- Chronic airway inflammation with remodeling
- Radiography
  - Most patients have normal or near normal radiographs
  - Bronchial wall thickening may be evident
  - Pulmonary hyperinflation in severe cases
- CT
  - Bronchial wall thickening
  - Bronchial luminal narrowing
  - Air-trapping (expiratory CT)
  - Allergic bronchopulmonary aspergillosis should be considered with central bronchiectasis and mucoid impaction
Pulmonary Langerhans Cell Histiocytosis
- Nearly all patients are smokers
- Radiography
  - Hyperinflation
  - Reticular or reticulonodular abnormality sparing costophrenic sulci
- CT
  - Upper lobe predominant cysts: Vary in size and shape
  - Small nodules ± central lucency progressing to cysts over time
  - Ground-glass opacity
- Spontaneous pneumothorax in < 10%
Lymphangiomyomatosis
- Occurs exclusively in women of child-bearing age or patients with tuberous sclerosis
- Radiography
  - Hyperinflation
  - Diffuse reticular abnormality (from superimposition of cysts)
  - Pleural effusion (chylous)
- CT
  - Diffuse lung cysts ranging 2-20 mm with thin, smooth walls
  - Associated findings: Renal angiomyolipomas, retroperitoneal and mediastinal lymphangiomas, chylous pleural effusion
- Patients may present with recurrent or chronic pneumothoraces

Helpful Clues for Rare Diagnoses

Pulmonary Atresia
- Presents in neonatal period: Cyanosis
- Associated with other congenital cardiac malformations (e.g., tetralogy of Fallot)
- Radiography
  - Cardiomegaly
  - Concave pulmonary artery segment
  - Pulmonary oligemia
- Diagnosis usually confirmed by echocardiography or cardiac MR