Reticular Pattern

Eric J. Stern, MD

DIFFERENTIAL DIAGNOSIS

Common

Idiopathic Pulmonary Fibrosis (IPF)
Pulmonary Edema
Nonspecific Interstitial Pneumonitis (NSIP)
Connective Tissue Diseases
- Scleroderma
- Rheumatoid Arthritis
Sarcoidosis
Asbestosis

Less Common

Chronic Hypersensitivity Pneumonitis
Drug-Induced Lung Disease
Polymyositis/Dermatomyositis
Lymphangitic Carcinomatosis

Rare but Important

Diffuse Pulmonary Lymphangiomatosis

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Reticular pattern
- Pattern produced by innumerable interlacing small linear opacities
  - Resembles fisherman’s net; mesh-like
  - Fine, medium, or coarse reticulation may reflect disease progression
- Connotation for pattern on chest radiographs similar; however, summation of cystic spaces may result in reticular pattern
- HRCT specific components
  - Small, irregular linear opacities
  - Irregular interlobular septal thickening
  - Irregular intralobular linear opacities; interstitial thickening within secondary pulmonary lobule, usually fibrosis
  - Architectural distortion, traction bronchiectasis, and bronchiolectasis, due to fibrosis

Helpful Clues for Common Diagnoses

Idiopathic Pulmonary Fibrosis (IPF)
- Common interstitial lung disease of unknown etiology
- Pathologically has usual interstitial pneumonia (UIP) pattern
- Bilateral, symmetric, patchy reticular pattern; may involve all lobes but most severe in subpleural lung and lung bases
  - Traction bronchiectasis and bronchiolectasis; architectural distortion; irregular interfaces with pleural, vascular, and bronchial structures
- Subpleural honeycombing often present (air-containing cysts measuring 2-25 mm)
Pulmonary Edema
- Smooth thickening of interlobular septa and bronchovascular bundles; gravity-dependent ground-glass opacities &/or consolidation
- Associated cardiomegaly, pleural effusions
- Rapidly evolves; may resolve quickly with diuretics
Nonspecific Interstitial Pneumonitis (NSIP)
- Most commonly in patients with connective tissue disease (scleroderma, rheumatoid arthritis) and drug-related lung disease
- Histologic pattern of interstitial fibrosis and inflammation
- Extent of ground-glass opacities > reticular opacities
- Traction bronchiectasis usually out of proportion to severity of reticular opacities
- Honeycombing uncommon
- Distribution: Lower lung zones (60-90%), peripheral lung (50-70%); may be diffuse
  - Sparing of immediate subpleural lung in dorsal aspect of lower lobes (50%)
Scleroderma
- Pattern typically NSIP; UIP pattern less common
- Dilated esophagus common
- Consolidation may occur due to
  - Pneumonia, aspiration, organizing pneumonia, diffuse alveolar damage, diffuse pulmonary hemorrhage
Rheumatoid Arthritis
- Findings of NSIP (ground-glass opacities, fine reticulation), UIP pattern less common
- Osseous erosions may be evident in humeral heads or sternoclavicular joints
Sarcoidosis
- Reticular pattern more common with end-stage fibrotic disease (stage IV)
- Extensive reticulation, mainly involving perihilar regions of upper and middle lung zones; cystic changes may occur
- Architectural distortion, traction bronchiectasis, superior hilar retraction, compensatory overinflation of lower lobes
- Small perilymphatic nodules may be present in less involved lung
- Hilar and mediastinal adenopathy, common in early sarcoidosis; usually has resolved with extensive fibrosis
Asbestosis
- Irregular thickening of inter- and intralobular septa, subpleural curvilinear opacities, parenchymal bands
- Predominantly involves peripheral and dorsal aspects of lower lung zones
- Frequently associated pleural plaques (90%)
- Occupational exposure important

Helpful Clues for Less Common Diagnoses

Chronic Hypersensitivity Pneumonitis
- Mid-lung predominance most common, especially in those with low-level continuous antigen exposure (bird breeders)
- Upper lung zone predominance more common in those with intermittent exposure (farmers)
- Fibrosis: Irregular linear opacities (40%), traction bronchiectasis (20%)
- Often superimposed subacute findings
  - Poorly defined centrilobular opacities, ground-glass opacities, lobular areas of air-trapping
Drug-Induced Lung Disease
- Produces wide array of injury patterns, including reticular pattern
- Reticular pattern may be due to UIP, NSIP, or pulmonary edema
Polymyositis/Dermatomyositis
- Symmetric basal reticular opacities, architectural distortion, irregular bronchovascular thickening; may progress to honeycombing
- Early stages: Ground-glass opacities; bilateral, symmetric basal distribution
Lymphangitic Carcinomatosis
- Smooth &/or nodular thickening of interlobular septa, bronchovascular bundles, interlobar fissures, and subpleural interstitium
- Distribution: Often spares lobe or whole lung
- May have pleural effusions and mediastinal adenopathy
- Usually known history of previous malignancy

Helpful Clues for Rare Diagnoses

Diffuse Pulmonary Lymphangiomatosis
- a.k.a. lymphangiectasis
- Smooth, uniform thickening of interlobular septa and fissures
- Marked, smooth thickening of bronchovascular bundles
- Diffuse effacement of mediastinal fat and enlarged mediastinal lymph nodes key to recognition