Basilar Lung Zone Disease Distribution

Jeffrey P. Kanne, MD

DIFFERENTIAL DIAGNOSIS

Common

Idiopathic Pulmonary Fibrosis
Nonspecific Interstitial Pneumonitis
Aspiration

Less Common

Cryptogenic Organizing Pneumonia
Asbestosis

Rare but Important

Alpha-1 Antiprotease Deficiency
Desquamative Interstitial Pneumonia
Immotile Cilia Syndrome

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Tobacco abuse
- Desquamative interstitial pneumonia (90% are smokers)
- Alpha-1 antiprotease deficiency
Occupational exposures
- Asbestosis
- Desquamative interstitial pneumonia (dusts, fumes)

Helpful Clues for Common Diagnoses

Idiopathic Pulmonary Fibrosis
- Characterized histologically by usual interstitial pneumonia (UIP)
  - Temporal and spatial heterogeneity
  - Fibroblastic foci
- Radiographic findings
  - Honeycombing
  - Reticulation
  - Traction bronchiectasis and bronchiolectasis
  - Architectural distortion
- Subpleural and basal predominant
Nonspecific Interstitial Pneumonitis
- Histological pattern of interstitial inflammation characterized by
  - Spatial and temporal heterogeneity
  - Cellular, mixed, and fibrotic forms
- Most patients have collagen vascular disease (especially scleroderma, mixed connective tissue disease, and polymyositis)
- Other causes of nonspecific interstitial pneumonitis (NSIP) pattern
  - Idiopathic (especially in young women of east Asian ethnicity)
  - Drug toxicity
  - Familial fibrosis
  - Hypersensitivity pneumonitis
  - Cigarette smoking (rare cause)
- Radiographic findings
  - Basal predominant ground-glass opacity
  - Superimposed reticulation
  - Subpleural sparing (suggestive of diagnosis)
  - Traction bronchiectasis and bronchiolectasis (usually mild)
  - Esophageal dilation (scleroderma and mixed connective tissue disease)
Aspiration
- Ranges from innocuous intake of solids or liquids into airways to extensive lung injury
- Common causes
  - Alcohol and drug abuse
  - Neuromuscular disease
  - Loss of consciousness
  - Disorders of esophagus and pharynx, reflux disease
- Radiographic findings
  - Consolidation in dependent portions of lungs, often peribronchial
  - May lead to lung abscess formation (cavitation with fluid level)
  - Associated bronchial wall thickening, endobronchial debris, centrilobular nodules, and tree-in-bud opacities
  - Esophageal dilation or retained debris or liquid in esophagus suggestive

Helpful Clues for Less Common Diagnoses

Cryptogenic Organizing Pneumonia
- Histologic pattern defined by
  - Granulation tissue polyps in lumens of alveolar ducts and surrounding alveoli
- Common causes of organizing pneumonia
  - Connective tissue disease
  - Drug reaction
  - Infection
  - Inhalational injury
- Radiographic findings
  - Bilateral symmetric or asymmetric lung consolidation ± air bronchograms
  - Mid and basal lung zone predominance
  - Subpleural or peribronchial (60-80%) distribution
  - Perilobular (60%) distribution
  - Reverse halo or atoll sign (20%)
  - Ground-glass opacity (more common in immunocompromised patients)
Asbestosis
- Interstitial fibrosis from asbestos exposure
  - Histological similar to UIP
- Subpleural branching opacities (fibrosis centered on respiratory bronchioles where asbestos fibers deposited) earliest finding on CT
- Honeycombing less common except in severe disease
- Associated features
  - Parenchymal bands and subpleural curvilinear opacities
  - Calcified or noncalcified pleural plaques
  - Subpleural reticulation
  - Tractions bronchiectasis and bronchiolectasis
  - Architectural distortion

Helpful Clues for Rare Diagnoses

Alpha-1 Antiprotease Deficiency
- Accounts for < 1% of patients with chronic obstructive pulmonary disease (COPD)
- Homozygous deficiency (PiZZ) increases risk of COPD 30x
- Cigarette smoking major contributory factor
- Manifests in lungs as panlobular (panacinar) emphysema
- Radiographic findings
  - Hyperinflation
  - Ill-defined absence of normal lung, wispy “cotton candy” lung markings
  - Homogeneous appearance
  - Marked basal predominance
Desquamative Interstitial Pneumonia
- Histologic pattern of widespread accumulation of intraalveolar pigmented macrophages
- Heavy smokers (90%)
- Other causes of desquamative interstitial pneumonia-like reaction
  - Dust inhalation
  - Drug reaction
  - Connective tissue disease
- Radiographic findings
  - Basal predominant ground-glass opacity (75%)
  - Subpleural distribution (50%)
  - Mild reticulation
Immotile Cilia Syndrome
- Autosomal recessive disorders of ciliary structure and function
- Patients predisposed to sinusitis, recurrent respiratory tract infections, bronchiectasis, and infertility
- Situs abnormalities occur in up to 50%
- Radiographic findings
  - Situs inversus or heterotaxy
  - Bronchiectasis (50% lower lobe predominant)
  - Centrilobular nodules and tree-in-bud opacities