The Common Vein

Anatomical Distribution of Smoking-Related Lung Diseases

This table categorizes smoking-related lung diseases by their predominant lung distribution—starting with upper lobes and then lower lobes—along with their pathology and imaging features.

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Smoking-Related Diseases Affecting the Upper Lobes

Disease	Primary Location	Pathology	Imaging Features (HRCT/CXR)
Centrilobular Emphysema	Upper lobes	– Destruction of respiratory bronchioles – Loss of alveolar walls – Air trapping and hyperinflation	Patchy – Centrilobular lucencies (“holes”) – Hyperinflation, flattened diaphragm – Decreased vascular markings
Langerhans Cell Histiocytosis (PLCH)	Upper and mid lung zones	– Langerhans cell proliferation – Cystic lung disease with stellate scars – Nodular infiltrates, often cavitary	– Multiple irregular cysts – Upper lobe nodules ± cavitation
Respiratory Bronchiolitis-Interstitial Lung Disease (RB-ILD)	Upper lobes	– Smoker’s macrophages in respiratory bronchioles – Mild interstitial fibrosis	– Centrilobular ground-glass nodules – Patchy interstitial fibrosis
Lung Cancer (Squamous Cell, Small Cell)	Central & Upper lobes	– Squamous cell carcinoma → often central (near hilum) – Small cell lung cancer (SCLC) → aggressive, mediastinal involvement	– Hilar mass (Squamous, SCLC) – Cavitary lesion (Squamous cell) – Upper lobe consolidation (Adenocarcinoma subtype possible but less common)

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Smoking-Related Diseases Affecting the Lower Lobes

Disease	Primary Location	Pathology	Imaging Features (HRCT/CXR)
Chronic Bronchitis	Lower lobes	– Mucus hypersecretion – Goblet cell hyperplasia – Chronic airway inflammation and fibrosis	– Increased bronchovascular markings – Bronchial wall thickening – Lower lobe predominance
Smoker’s Bronchiolitis	Lower lobes	– Chronic small airway inflammation – Goblet cell hyperplasia → Excess mucus – Mild peribronchiolar fibrosis	– Bronchial wall thickening – Air trapping on expiratory CT – Lower lobe predominance
Desquamative Interstitial Pneumonia (DIP)	Lower lobes (diffuse alveolar involvement)	– Accumulation of macrophages in alveoli – Mild fibrosis of interstitium	– Lower lobe-predominant ground-glass opacities – Diffuse interstitial involvement
Lung Cancer (Adenocarcinoma)	Peripheral Lower lobes	– Adenocarcinoma is the most common lung cancer overall – More frequent in lower lobes due to slower clearance of carcinogens	– Peripheral lung nodule or mass – May show ground-glass opacities in early stages

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Key Takeaways:

1. Upper Lobes → More prone to oxidative stress & poor perfusion:

   • Diseases caused by gaseous toxins (Emphysema, PLCH, RB-ILD) occur higher in the lung because lighter gases rise with convection currents.
   • Lung cancer (Squamous, SCLC) commonly arises centrally in the upper lung zones.

2. Lower Lobes → More affected by particulate deposition & mucus trapping:

   • Chronic bronchitis and smoker’s bronchiolitis occur lower in the lungs due to gravity-driven deposition of inhaled particulates.
   • Adenocarcinoma (the most common lung cancer type) is more frequent peripherally in lower lobes, as carcinogens persist longer in these areas.