A CT scan, or Computed Tomography scan, provides detailed cross-sectional views of the body. Medical reports sometimes include terms like “air trapping” that can be unclear. This article clarifies what “air trapping” signifies on a CT scan, explaining its physiological basis, visualization, common causes, and health implications.
Understanding Air Trapping
Air trapping refers to the abnormal retention of air within the lungs after exhalation. Normally, the lungs’ tiny air sacs, called alveoli, expand during inhalation and recoil to expel air during exhalation, ensuring continuous oxygen and carbon dioxide exchange.
When air trapping occurs, structures like small airways or alveoli do not function properly. This prevents complete lung emptying, causing air to accumulate with each breath. This retention can lead to an inflated feeling and shortness of breath, as the lungs become overinflated.
Identifying Air Trapping on a CT Scan
Radiologists identify air trapping on a CT scan by looking for specific visual cues, particularly on images taken during exhalation. In a normal exhalation, lung tissue becomes denser as air is expelled and its volume decreases. Areas of air trapping, however, appear as regions of decreased attenuation, remaining darker than surrounding normal lung tissue.
Air trapping often presents as a “mosaic attenuation pattern” on expiratory CT scans, with some lung areas appearing less dense than others. To confirm air trapping, radiologists often compare images taken during both inspiration and full exhalation. This comparison highlights areas that fail to deflate normally.
Common Causes of Air Trapping
Air trapping is frequently associated with obstructive lung diseases, where the airways narrow or are damaged, impeding airflow. One common cause is asthma, a chronic condition characterized by airway inflammation and narrowing. In asthma, airways can become obstructed by mucus and inflammation, preventing full exhalation.
Chronic Obstructive Pulmonary Disease (COPD), which includes conditions like emphysema and chronic bronchitis, is another prevalent cause. In emphysema, the walls of the alveoli are damaged and lose their elasticity, making it difficult for the lungs to deflate. Chronic bronchitis involves inflammation and excessive mucus production in the bronchial tubes, narrowing the airways and trapping air. Bronchiolitis, an inflammation of the small airways, particularly common in infants, can also lead to air trapping due to airway obstruction from inflammation and mucus.
Why Air Trapping Matters
Identifying air trapping on a CT scan holds significant diagnostic value for healthcare providers. It serves as an indicator of underlying lung issues, particularly small airway disease or other forms of airway obstruction. Even when other imaging findings appear normal on inspiratory scans, air trapping revealed on expiratory CT can signal an early stage of lung disease.
The presence and extent of air trapping can help doctors understand the nature and severity of certain lung conditions. For example, it is a characteristic feature of severe asthma and is associated with a higher risk of exacerbations in COPD. This information aids in guiding further diagnostic evaluations and informs decisions regarding patient management.