Emphysema, or pulmonary emphysema, is a lower respiratory tract disease, characterised by air-filled spaces (pneumatoses) in the lungs, that can vary in size and may be very large. The spaces are caused by the breakdown of the walls of the alveoli and they replace the spongy lung parenchyma. This reduces the total alveolar surface available for gas exchange leading to a reduction in oxygen supply for the blood. Emphysema usually affects the middle aged or older population because it takes time to develop with the effects of tobacco smoking, and other risk factors. Alpha-1 antitrypsin deficiency is a genetic risk factor that may lead to the condition presenting earlier.When associated with significant airflow limitation, emphysema is a major subtype of chronic obstructive pulmonary disease (COPD), a progressive lung disease characterized by long-term breathing problems and poor airflow. Without COPD, the finding of emphysema on a CT lung scan still confers a higher mortality risk in tobacco smokers. In 2016 in the United States there were 6,977 deaths from emphysema – 2.2 per 100,000 of the population. Globally it accounts for 5% of all deaths. A study on the effects of tobacco and cannabis smoking showed that a possibly cumulative toxic effect could be a risk factor for developing emphysema, and spontaneous pneumothorax.There are four types of emphysema, three of which are related to the anatomy of the lobules of the lung – centrilobular or centriacinar, panlobular or panacinar, and paraseptal or distal acinar emphysema, and are not associated with fibrosis (scarring).
Contrast-enhanced CT is useful in assessing vascular abnormalities and mediastinal masses. Focal
Focal emphysema, is a localized region of emphysema in the lung that is larger than alveoli, and often associated with coalworkers pneumoconiosis. This is also known as localized pulmonary emphysema. Blebs and bullae may also be included as focal emphysema. These can be differentiated from the other type of enclosed air space known as a lung cyst by their size and wall thickness. A bleb or bulla  has a wall thickness of less than 1 mm, and are smaller. Occupational
A number of occupations are associated with the development of emphysema due to the inhalation of varied gases and particles. In the US uranium mining that releases radon gas and particles has been shown to be a cause of emphysema deaths; the figures in the study included some miners who also smoked. Uranium mining and milling was found to create environmental pollution.The inhalation of coal mine dust that can result in coalworkers pneumoconiosis is an independent risk factor for the development of emphysema. Focal emphysema is associated with the coal macule, and this extends into progressive centrilobular emphysema. Less commonly a variant of panlobular emphysema develops.Silicosis results from the inhalation of silica particles, and the formation of large silica nodules is associated with paracicatricial emphysema, with or without bullae. Ozone-induced emphysema
Ozone is another pollutant that can affect the respiratory system. Long-term exposure to ozone can result in emphysema. Osteoporosis
Osteoporosis is a major comorbidity of emphysema. Both conditions are associated with a low body mass index.