Emphysema on CT Imaging: Key Features, Types, and Clinical Implications

Emphysema is a chronic lung condition characterized by the destruction of alveolar walls and loss of lung elasticity, often associated with long-term smoking or chronic obstructive pulmonary disease (COPD). One of the most effective tools for diagnosing and classifying emphysema is computed tomography (CT) scanning. CT imaging provides detailed visualization of structural changes in the lungs, allowing clinicians to identify specific patterns and subtypes of the disease.

Common CT Findings in Emphysema

1. Pulmonary Hyperinflation and Low-Attenuation Areas: A hallmark of emphysema on CT scans is lung overinflation, which appears as abnormally low-density (low-attenuation) regions throughout the lung parenchyma. These dark areas reflect the destruction of alveoli and reduced tissue density due to air trapping.

2. Reduced CT Attenuation Values and Vascular Changes: The CT attenuation values in affected regions are significantly lower than normal lung tissue—often below -950 Hounsfield units on inspiratory scans. Additionally, the peripheral pulmonary vessels appear thinner and sparser due to the loss of supporting lung architecture.

3. Enlarged Central Pulmonary Vessels: In contrast to the diminished peripheral vasculature, the central pulmonary arteries near the hila may appear enlarged. This finding can indicate the development of pulmonary hypertension, a common complication in advanced emphysema.

Main Types of Emphysema Identified on CT Scans

1. Panacinar (Panlobular) Emphysema

This type affects the entire acinus uniformly and is most commonly seen in patients with alpha-1 antitrypsin deficiency. On CT, it presents as widespread, irregular low-attenuation zones, particularly predominant in the lower lobes. The surrounding blood vessels are not only reduced in number but also show distortion due to tissue destruction.

2. Centrilobular (Centriacinar) Emphysema

The most prevalent form, especially among smokers, centrilobular emphysema primarily damages the respiratory bronchioles in the center of the pulmonary lobule. CT scans reveal scattered, small (2–10 mm), patchy or nodular low-density areas, typically more prominent in the upper and middle lung zones. These lesions often coexist with signs of small airway disease.

3. Paraseptal (Distal Acinar) Emphysema

This subtype is localized near the pleura and along the interlobular septa. It frequently leads to the formation of bullae—air-filled spaces larger than 1 cm in diameter. These bullae can be solitary or clustered and are strongly associated with spontaneous pneumothorax, especially in young adults.

4. Irregular (Scar) Emphysema

Irregular emphysema develops adjacent to areas of fibrosis or scarring caused by prior lung injuries such as tuberculosis, pneumoconiosis, or healed pneumonia. CT imaging shows focal regions of abnormal low attenuation interspersed with dense fibrotic tracts. These areas often display a "honeycombing" pattern, indicating combined parenchymal destruction and architectural remodeling. Bronchiectasis may also be present in these zones due to structural damage.

Bullous Emphysema: A Special Consideration

When emphysematous changes result in large airspaces exceeding 1 cm in diameter, the condition is classified as bullous emphysema. These bullae can occupy significant portions of the lung, compressing healthy tissue and impairing respiratory function. Patients with extensive bullae are at increased risk for complications such as infection, rupture, and life-threatening pneumothorax.

Accurate interpretation of CT findings is essential for differentiating emphysema subtypes, guiding treatment decisions, and predicting clinical outcomes. Radiologists and pulmonologists use these imaging patterns to tailor management strategies, including smoking cessation programs, pulmonary rehabilitation, oxygen therapy, and, in severe cases, surgical interventions like lung volume reduction surgery or transplantation.

In conclusion, CT imaging plays a pivotal role in the diagnosis and classification of emphysema. Recognizing the distinct radiological features of each subtype enables early detection, better patient stratification, and improved long-term care for individuals suffering from this progressive lung disease.