Diseases of the lung can be classified into four general categories:
1. Obstructive lung disease (COPD); in which air is trapped within the parenchyma; it includes emphysema, asthma, bronchiectasis and chronic bronchitis.
2. Restrictive lung disease; in which airway filling is impaired due to fibrosis of alveolar septae.
3. Infections; which range from mild self-limiting conditions like common cold to life threatening diseases such as bacterial pneumonias.
4. Neoplasms; Benign tumors are relatively rare while malignant tumors include primary tumors and secondary deposits.