What does increased bronchial markings on imaging indicate?

Increased Bronchial Markings on Imaging

Increased bronchial markings on chest radiography represent bronchial wall thickening, which is a nonspecific finding indicating airway inflammation or chronic irritation, most commonly from cigarette smoking, but requiring CT imaging for definitive characterization and to exclude bronchiectasis or other significant airway pathology. 1, 2

What Increased Bronchial Markings Indicate

Primary Pathophysiology

• Bronchial wall thickening is the morphological substrate underlying increased bronchial markings on chest radiography, representing the airways' common final response to irritants causing swelling and inflammation 3, 4
• The finding correlates directly with cigarette consumption measured in pack-years (r=0.68), with 74% of smokers demonstrating this pattern 5
• This appearance has been termed "dirty chest" in the radiology literature, reflecting the overall increase in nonspecific lung markings 5

Clinical Significance

• Bronchial wall thickening correlates with exacerbation frequency (r=0.32) and remains a significant determinant of airflow obstruction on multivariate analysis 6
• The severity of wall thickening associates with 24-hour sputum volume (r=0.30) and measures of airflow obstruction including FEV₁, FEV₁/FVC ratio, and FEF₂₅₋₇₅% 6
• In COPD patients, bronchial wall thickening can be identified on CT and helps differentiate structural abnormalities causing airflow limitation 1

Critical Limitation: Chest Radiography is Inadequate

Why CT is Essential

• Chest radiography is relatively insensitive for detecting underlying bronchiectasis, with up to 34% of chest radiographs interpreted as normal in patients with CT-confirmed bronchiectasis 2
• Linear opacities and fibro-atelectatic plaques visible on radiography may mask underlying bronchiectasis, making the increased markings falsely reassuring 2
• Chest radiography provides limited characterization of severity and morphology of airway disease 2

When to Obtain CT

• Non-contrast CT with 1.5mm thin slices is the reference standard for detecting bronchiectasis, characterized by bronchi wider than adjacent arteries, absence of normal bronchial tapering, or bronchi within 1cm of pleural surface 2
• The 2010 British Thoracic Society guidelines recommend high-resolution CT as the examination of choice for evaluating suspected bronchiectasis 2
• CT should be obtained when increased bronchial markings are present on radiography to confirm or exclude bronchiectasis, especially with linear opacities or fibro-atelectatic plaques 2

Differential Diagnosis Based on CT Findings

If CT Shows Bronchiectasis

• Cystic fibrosis: cylindrical bronchiectasis with varicose and cystic forms in advanced cases, bronchial wall thickening, and mucus plugs 4
• Allergic bronchopulmonary aspergillosis: central varicose or cystic bronchiectasis, predominantly upper lobes, with mucoid impaction 4
• Post-infectious: childhood viral infection as a common cause 4
• Traction bronchiectasis: associated with pulmonary fibrosis, where increased reticulation and architectural distortion cause secondary bronchial dilation 1, 4

If CT Shows Isolated Bronchial Wall Thickening

• Asthma: characterized by bronchial wall thickening due to inflammation, with possible bronchial dilatation and air trapping 4
• Chronic bronchitis from smoking: most common cause, with intralobular opacities (61%) and emphysema (62%) frequently coexisting 5
• Bronchiolitis: may show centrilobular branching structures, nodules, mosaic perfusion, and air trapping 4

Prognostic Implications

CT Quantification Matters

• Involvement of ≥3 lobes on CT is associated with poorer prognosis in bronchiectasis patients 2
• The severity of bronchiectasis on CT correlates with measures of airway obstruction, making quantification clinically relevant 2, 6
• CT allows precise quantification of extent and severity using various validated scoring systems 2

Associated Findings to Report

• Emphysema extent >15% must be reported as it associates with comorbidities, higher risk of complications (pulmonary hypertension, lung cancer), and disease progression 1
• Presence of traction bronchiectasis/bronchiolectasis indicates fibrosis and has prognostic value 1
• Mosaic attenuation pattern correlates with airflow obstruction (r=-0.43 to -0.60 for FEV₁) 6

Common Pitfalls to Avoid

• Do not dismiss increased bronchial markings as "chronic changes" without CT confirmation, as this misses 34% of bronchiectasis cases 2
• Do not attribute all increased markings to smoking without excluding treatable causes like bronchiectasis requiring specific management 2, 4
• Do not rely on chest radiography alone for characterizing the extent or type of airway disease, as it underestimates disease burden 2, 7
• In patients with pulmonary fibrosis patterns, recognize that increased markings may represent traction bronchiectasis requiring different management than infectious bronchiectasis 1