Idiopathic Pulmonary Fibrosis

C. Nicholas Fetko, MD

Aqeel A. Chowdhry, MD

Tan-Lucien H. Mohammed, MD, FCCP

Key Facts

Terminology

Idiopathic interstitial pneumonias of unknown cause
- Associated with histologic pattern of usual interstitial pneumonia on surgical biopsy

Imaging Findings

Subpleural and basal honeycombing and traction bronchiectasis
- Reticular opacities > > ground-glass opacities
Consider alternative diagnosis to IPF if centrilobular nodules, cysts, extensive ground-glass opacities, consolidation, peribronchovascular distribution
Acute exacerbation
- New ground-glass opacities or consolidation
- Peripheral (60%), diffuse (25%), multifocal (15%)
Positive predictive value of confident diagnosis = 95-100%

Top Differential Diagnoses

Nonspecific Interstitial Pneumonitis
Asbestosis
Chronic Hypersensitivity Pneumonitis
Drug Reaction

Pathology

Usual interstitial pneumonia histologic pattern characterized by spatial and temporal heterogeneity

Clinical Issues

Median survival following diagnosis about 3.5 years
Transplantation only effective treatment

Diagnostic Checklist

Drug reaction in any patient with IPF pattern

Axial HRCT shows the typical pattern of severe peripheral honeycombing

and traction bronchiectasis

in idiopathic pulmonary fibrosis.

Coronal HRCT reconstruction shows basilar honeycombing

. Ground-glass opacities are minimal, and the lower lobes have lost volume.

TERMINOLOGY

Abbreviations and Synonyms

Idiopathic pulmonary fibrosis (IPF), cryptogenic fibrosing alveolitis (CFA), usual interstitial pneumonia (UIP)

Definitions

Most common form of idiopathic interstitial pneumonias
- Associated with histologic pattern of usual interstitial pneumonia on surgical biopsy

IMAGING FINDINGS

General Features

Best diagnostic clue: Subpleural and basal honeycombing and traction bronchiectasis
Patient position/location
- Subpleural and basilar lung
  - Costophrenic angles should be most affected portion of lungs
Morphology
- Reticular opacities, honeycombing, traction bronchiectasis
- Relative lack of ground-glass opacities

CT Findings

Morphology
- Predominant reticular pattern with honeycombing
  - Peripheral honeycomb cysts may vary in size, dependent on phase of respiratory cycle
  - Traction bronchiectasis or bronchiolectasis essential to diagnosis
- Ground-glass opacities
  - Reticular opacities > > ground-glass opacities
  - Minor component of overall pattern
- Emphysema: Coexistent centrilobular or paraseptal emphysema in about 30%
- Pulmonary ossification may occur in long-standing fibrosis
- Consider alternative diagnosis to IPF if centrilobular nodules, cysts, extensive ground-glass opacities, consolidation, peribronchovascular distribution
Distribution
- Basal and peripheral predominance
- Patchy, heterogeneous distribution abuts normal lung
- May be asymmetric, but not unilateral
- Mean extent of disease 25% ± 10%
Volume loss prominent with honeycombing
Pulmonary artery enlargement
- Reflects pulmonary artery hypertension seen in 50% of those undergoing pre-transplant evaluation
- Other findings include right ventricular wall hypertrophy, dilatation of right ventricle and atrium, contrast reflux into inferior vena cava, and hepatic veins
Adenopathy (50%)
- Mediastinal lymph node enlargement < 2 cm short axis diameter
- Most common location right paratracheal nodal station (American Thoracic Society [ATS] region 4) or subcarinal (ATS region 7)
- Frequency related to extent of fibrosis and duration of disease
Complications
- Acute exacerbation
  - Morphology: New ground-glass opacities or consolidation
  - Distribution: Peripheral (60%), diffuse (25%), multifocal (15%)
  - Generally spares honeycomb lung
- Bronchogenic carcinoma
  - Seen in up to 10% of patients with long-standing IPF
  - Typical appearance: Focal consolidation in periphery of lower lobes in area of severe fibrosis
  - May be multiple
- Barotrauma: Increased risk for pneumothorax, pneumomediastinum
- Infection: Higher risk for mycobacterial species, Aspergillus, and other organisms
  - Suspect infection with progressive consolidation or cavitation
Accuracy
- Should make confident diagnosis in 50% of cases
- Positive predictive value of confident diagnosis = 95-100%
  - Interestingly, interobserver agreement of presence of honeycombing only about 70%

Radiographic Findings

Radiography: Not as specific as CT but usually abnormal

Imaging Recommendations

Best imaging tool: HRCT to detect and characterize interstitial lung disease

DIFFERENTIAL DIAGNOSIS

Nonspecific Interstitial Pneumonitis

Ground-glass opacities > > reticular pattern
Traction bronchiectasis out of proportion to extent of reticular opacities
Bronchovascular distribution more common
Honeycombing not as prominent
Traction bronchiectasis extends into more central airways with IPF

Asbestosis

Subpleural reticular pattern with honeycombing identical to IPF
Fibrosis in asbestosis may be coarser than in IPF
Subpleural curvilinear lines, mosaic perfusion, and parenchymal bands more common
Associated (calcified) pleural plaques
Bronchiolectasis more common in IPF

Chronic Hypersensitivity Pneumonitis

Inferior costophrenic angles not most severely involved lung (usually mid and upper lung)
Centrilobular nodules, lobular air-trapping more common

Rheumatoid Arthritis

Pulmonary fibrosis difficult to distinguish from IPF
Erosive arthritis not seen with IPF
More frequently associated with nonspecific interstitial pneumonia (NSIP) pattern

Systemic Sclerosis