Nemec SF, Bankier AA, Eisenberg RL. Upper Lobe–Predominant Diseases of the Lung. American Journal of Roentgenology. 2013;200(3):W222-W237. doi:10.2214/AJR.12.8961

Background

• In an erect individual, the lung apex is relatively overventilated (ratio of ventilation to perfusion, 3:1), and the base is relatively overperfused (ratio, 0.6:1). Therefore, conditions caused by inhalation of toxic substances primarily affect the apices of the lung.
• Lymphatic particle clearance is relatively decreased in the apices because the lymphatic flow is driven by perfusion as well as respiratory excursion, both of which are relatively deceased in the upper lung zones. This explains why granulomatous disorders, such as tuberculosis or sarcoidosis, appear predominantly in the upper lobes.
• In addition, metabolic factors, such as regional uptake of oxygen, elimination of carbon dioxide, and pH in the lung, differ due to inequalities of the ventilation-perfusion ratio. These factors contribute to the upper zone predisposition of conditions such as metastatic pulmonary calcification and tuberculosis.
• Finally, increased mechanical stress of the pulmonary apices caused by a rigid chest cage may result in fibrobullous apical lesions, as in patients with ankylosing spondylitis.

Differential

Key Diseases to know: - inhalation injury - smoke - Centrilobular emphysema (from smoking) - Cystic fibrosis (due to impaired muciciliary clearance) - Pneumoconioses - Caplan syndrome - Inhaled antigens - Hypersensitivity pneumonitis - ABPA - Chronic eosinophilic penumonia - Granulomatous disease - TB - Sarcoidosis - Pulmonary LCH - Perfusion issues - Eccentric flash pulmonary edema - Neurogenic pulmonary edema - Rheumatic - Ankylosing spondylitis (due to increased mechanical stress)