Nonspecific Interstitial Pneumonia

Jud W. Gurney, MD, FACR

Tan-Lucien H. Mohammed, MD, FCCP

Key Facts

Terminology

1 of the idiopathic interstitial pneumonias, less common than idiopathic pulmonary fibrosis (IPF), but with better prognosis than IPF

Imaging Findings

Ground-glass opacities > reticular opacities
Traction bronchiectasis out of proportion to reticular opacities
May have fine honeycombing: Microcystic honeycombing
Distribution: Lower (92%), diffuse (60%)
- Peribronchovascular distribution, often fan-shaped
- Subpleural sparing (20%)
Up to 30% over 3-year period evolve to more UIP pattern

Top Differential Diagnoses

Idiopathic Pulmonary Fibrosis (IPF)
Hypersensitivity Pneumonitis
Cryptogenic Organizing Pneumonia (COP)

Pathology

Etiology
- Idiopathic
- Scleroderma
- Hypersensitivity pneumonia
- Drug-induced lung disease: Amiodarone
Concept that NSIP represents early stage of UIP now discounted

Clinical Issues

Average duration of symptoms prior to diagnosis: 7 months
5 year survival > 80%

Axial NECT shows peribronchial peripheral ground-glass opacities

, which exceed reticular opacities. Note the subpleural sparing

Coronal NECT shows basilar fan-shaped

ground-glass and reticular opacities extending along the bronchovascular pathways. Subpleural sparing

is noted in this patient with NSIP.

TERMINOLOGY

Abbreviations and Synonyms

Nonspecific interstitial pneumonia (NSIP)

Definitions

1 of the idiopathic interstitial pneumonias, less common than idiopathic pulmonary fibrosis (IPF), but with better prognosis than IPF
- Distinguished by temporal and spatial uniformity of histologic findings

IMAGING FINDINGS

General Features

Best diagnostic clue: Traction bronchiectasis out of proportion to reticular opacities
Patient position/location: Peribronchovascular basilar distribution
Size: Generally involves 25-35% of lung volume
Morphology: Ground-glass opacities > reticular opacities

CT Findings

Morphology
- Reticular opacities (85%)
  - Often admixed with ground-glass opacities
  - Ground-glass opacities, when present, usually exceed reticular opacities
  - Combined ground-glass opacities and reticular opacities may result in crazy-paving pattern
- Traction bronchiectasis (80%)
  - Often out of proportion to degree of reticular opacities
  - Usually associated with considerable lobar volume loss
  - Mean 20% of total lung volume
- Ground-glass opacities (75%)
  - Ground-glass opacities often exceed reticular opacities, especially early
  - Mean 25-35% of lung volume with ground-glass opacities
  - May have mosaic perfusion pattern (5%)
- Peribronchial thickening (5%)
- Honeycombing rare (5%) (so uncommon, should suggest usual interstitial pneumonitis [UIP])
  - May have fine honeycombing: Microcystic honeycombing
  - Isolated enlarged airspaces may be present (not clustered together like honeycombing)
- Consolidation less common, mean 10% of lung volume
Distribution
- Symmetry common
- Craniocaudad
  - Lower (92%)
  - Diffuse (8%)
- Axial
  - Diffuse (60%)
  - Peripheral (35%)
- Subpleural sparing (20%)
  - Very thin rim
- Bronchovascular distribution, often fan-shaped from hilum to lung periphery
Evolution
- Up to 30% over 3-year period evolve to more UIP pattern
- Reversible findings: Ground-glass opacities, reticular opacities, traction bronchiectasis
Adenopathy (80%)
- 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)
- Direct positive correlation between extent of parenchymal involvement and presence of lymphadenopathy
Accuracy
- Should make confident diagnosis in 80% of cases
- Positive predictive value of confident diagnosis = 70-80%

Radiographic Findings

Radiography
- Radiography: Nonspecific, abnormal (90%)
- Bibasilar interstitial thickening (“lace-like” honeycombing)

Imaging Recommendations

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

DIFFERENTIAL DIAGNOSIS

Idiopathic Pulmonary Fibrosis (IPF)

Honeycombing more common
Subpleural peripheral location, more common
- No subpleural sparing
Ground-glass extent less common
Histopathology: Temporal inhomogeneity of lung injury
Poorer prognosis than NSIP

Hypersensitivity Pneumonitis

May have NSIP pattern
Occupational and home environmental history extremely important to discover known antigens
Mosaic perfusion pattern more common
Chronic disease usually more severe in mid and upper lung zones, honeycombing more common

Cryptogenic Organizing Pneumonia (COP)

Consolidation usually more prominent than in NSIP
May have multiple pulmonary nodules or single mass, uncommon with NSIP
Reverse halo sign not seen with NSIP
Reticular opacities uncommon but similar to NSIP

Desquamative Interstitial Pneumonia (DIP)

Smokers; smoking less common in NSIP
Diffuse ground-glass opacities with scattered cysts
Traction bronchiectasis uncommon

Pulmonary Alveolar Proteinosis (PAP)

“Crazy-paving” appearance, less common with NSIP
Central and geographic distribution, not bronchovascular or peripheral
No traction bronchiectasis

Sarcoidosis

Nodules: Most common pattern follows lymphatic pathways
- Centrilobular, bronchovascular, and subpleural
Occasionally have predominant ground-glass opacities
- Would not be associated with traction bronchiectasis if ground-glass opacities were predominant pattern
Adenopathy more common and nodes larger, especially in early disease