Respiratory Bronchiolitis

Martha Huller Maier, MD

Key Facts

Terminology

RB: Histologic reaction (pathologic in some) found in cigarette smokers
- Usually asymptomatic
RB-ILD: Clinicopathologic syndrome found in heavy smokers
RB, RB-ILD, and DIP are part of spectrum of smoking-related lung diseases

Imaging Findings

RB: Mild patchy ground-glass opacities and centrilobular nodules more commonly found in upper lobes
HRCT often normal (sensitivity 25%)
Longitudinal observation: RB may evolve into centrilobular emphysema

Top Differential Diagnoses

Pathology

Reactive accumulation of macrophages within lumen of respiratory bronchioles (2nd order) and surrounding alveoli

Clinical Issues

RB: Usually asymptomatic
RB: Universal histologic response in smokers, seen within 2 years of onset of smoking
M:F = 2:1

Axial HRCT shows ill-defined centrilobular ground-glass nodules

in the upper lobes. The patient had a mild cough and dyspnea with exercise.

Coronal HRCT reconstruction shows faint centrilobular nodules

in the upper lobes sparing the lower lung zones in this asymptomatic patient with a 40 pack-year smoking history.

TERMINOLOGY

Abbreviations and Synonyms

Definitions

RB: Histologic reaction (pathologic in some) found in cigarette smokers
- Usually asymptomatic
RB-ILD: Clinicopathologic syndrome found in heavy smokers
- RB is pathologic lesion found on lung biopsy in patients with clinical condition of RB-ILD
- Characterized by pulmonary symptoms, abnormal pulmonary function tests, and imaging abnormalities
- RB, RB-ILD, and DIP are part of the spectrum of smoking-related lung diseases

IMAGING FINDINGS

General Features

Best diagnostic clue
- RB: Mild patchy ground-glass opacities and centrilobular nodules more commonly found in upper lobes
- RB-ILD: RB findings become more pronounced and widespread, especially ground-glass opacities
  - Mild thickening of central and peripheral airways
Patient position/location
- RB: Nodules most numerous in upper lung zones, sparing lung bases
- RB-ILD: Distribution more extensive
  - May extend into lower lobes with coarse bibasilar bands of atelectasis and scarring
Size: Centrilobular nodules 3-5 mm in diameter
Morphology: Nodules generally ground-glass and ill defined

CT Findings

Respiratory bronchiolitis
- HRCT often normal (sensitivity 25%)
- Faint centrilobular micronodules (often overlooked)
- Patchy ground-glass opacities
- Predominantly upper lung zones
- May have associated centrilobular emphysema
Respiratory bronchiolitis-interstitial lung disease
- Upper lobe centrilobular nodules and patchy ground-glass opacities more pronounced
- Mild reticular opacities may be present in lower lobes
- Mild bronchial wall thickening
- Centrilobular emphysema commonly associated; probably correlates with increased pack-year history and older age
RB & RB-ILD may be combined with other sequelae of smoking (bronchogenic carcinoma, emphysema, DIP)
Longitudinal observations
- RB may evolve into centrilobular emphysema
- Explains chronology (RB early, centrilobular emphysema late)
- Explains location; both share location in 2nd order respiratory bronchiole and spatial distribution within upper lung zones

Radiographic Findings