Interstitial Pattern, Hyperinflation

Christopher M. Walker, MD

DIFFERENTIAL DIAGNOSIS

Common

Emphysema with Superimposed Process
Asthma
Viral or Atypical Pneumonia

Less Common

Cystic Fibrosis (Mimic)
Sarcoidosis

Rare but Important

Lymphangiomyomatosis
Pulmonary Langerhans Cell Histiocytosis

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Age, gender, and clinical presentation are key discriminators

Helpful Clues for Common Diagnoses

Emphysema with Superimposed Process
- Chronic bronchitis with bronchial wall thickening
- Pulmonary edema
- Pneumonia involving interstitium
- Interstitial lung disease
  - Usual interstitial pneumonia
  - Desquamative interstitial pneumonia
  - Respiratory bronchiolitis
Asthma
- Normal radiograph is most common radiographic manifestation during acute attack
- Radiographic findings slightly more common and more severe in children
  - Secondary to smaller diameter of bronchioles
- Radiographs show
  - Hyperinflated lungs
  - Areas of atelectasis secondary to mucus plugging of small airways
  - Bronchial wall thickening
- HRCT demonstrates
  - Bronchial wall thickening
  - Mosaic perfusion and air-trapping on expiratory images
  - Mucous plugging
  - May be complicated by allergic bronchopulmonary aspergillosis
Viral or Atypical Pneumonia
- Discriminators are age and symptoms of infection
- Causes hyperinflation in small children secondary to
  - Poorly developed collateral ventilation
  - Small airway diameter that easily plugs with mucus
  - More abundant mucus production
- Less frequent to see hyperinflation in adults
- Interstitial abnormality secondary to
  - Inflammation of small airways
  - Peribronchial edema
- Radiographic findings (more common in children)
  - Course markings radiating from hila into lungs (busy or dirty lungs)
  - Hyperinflation
  - Subsegmental atelectasis

Helpful Clues for Less Common Diagnoses

Cystic Fibrosis (Mimic)
- Common autosomal recessive disease
- Causes recurrent infections in children
- Early radiographic findings
  - Hyperinflation secondary to obstruction of small airways
  - Nodular or reticular opacities secondary to impaction of small airways
  - Tram-tracking indicating bronchial wall thickening or bronchiectasis
  - Upper lung predominant disease
- Late radiographic findings
  - Pulmonary hypertension
  - Cystic bronchiectasis with more diffuse distribution
  - Mucoid impaction of larger airways
  - Atelectasis
- HRCT findings
  - Bronchiectasis
  - Bronchial wall thickening
  - Tree-in-bud opacities secondary to mucoid impaction of small airways which ± indicate infection
  - Mucous plugging of larger airways
  - Mosaic perfusion and air-trapping on expiratory views indicates small airways involvement
Sarcoidosis
- Systemic granulomatous disease
- May involve almost any organ
- 90% have pulmonary involvement
- Radiographs demonstrate
  - Hilar and right paratracheal lymphadenopathy ± calcification
  - Well- or ill-defined nodules with upper lung predominance
  - Lungs may be hyperinflated secondary to small airways involvement by noncaseating granulomas
- HRCT findings
  - Upper lung predominance
  - Perilymphatic distribution of nodules (along fissures, subpleural lung, and bronchovascular bundles)
  - Uncommonly a random distribution of nodules
  - Nodular bronchial wall thickening
  - Small airways involvement demonstrated by mosaic perfusion or air-trapping

Helpful Clues for Rare Diagnoses

Lymphangiomyomatosis
- Exclusively women of childbearing age
- May exacerbate during pregnancy
- Identical disease can be seen in tuberous sclerosis
- Radiographic findings
  - Normal or large lungs
  - Normal radiograph early
  - Fine or coarse reticular opacities with diffuse distribution
  - Pneumothorax (up to 80%)
  - Pleural effusions (chylous)
- HRCT findings
  - Diffuse distribution of round cysts
  - Cysts start small and increase in size with disease progression
  - ± chylous pleural effusions (indistinguishable from simple pleural fluid)
  - ± pneumothorax
  - 10-15% have angiomyolipomas in kidneys
  - ± mediastinal or retroperitoneal lymphadenopathy
Pulmonary Langerhans Cell Histiocytosis
- 20-40-year-old male Caucasian cigarette smoker presenting with cough and dyspnea
- Peribronchiolar proliferation of Langerhans cells
- Radiographic findings
  - Nodular or reticulonodular opacities in upper 2/3 of lung
  - Preserved or increased lung volumes
  - Spares lung bases
  - 30% have pneumothoraces
- HRCT findings
  - Centrilobular nodules ± central cavities
  - Cystic spaces ≤ 10 mm in diameter
  - Round or bizarrely shaped cysts
  - Spares costophrenic sulci
  - ± pneumothorax
  - Rare association with lytic bone lesions
  - Disease progresses from nodules to cavitating nodules to cysts
  - Cysts thought to represent enlarged airway lumina (paracicatricial emphysema)

Image Gallery

Frontal radiograph shows increased linear opacities bilaterally, representing bronchial wall thickening, and increased lucency in the right upper lung