Radiological Findings of Emphysema

Introduction:

Emphysema is a chronic obstructive pulmonary disease that affects the air sacs (alveoli) of the lungs and causes breathing difficulties. Alveoli are tiny, thin-walled air sacs found as clusters at the end of the lungs' bronchial tubes. While breathing in the oxygen, the alveoli stretch, draw the air and transport it to the blood. Chronic obstructive pulmonary disease is a group of inflammatory diseases that include emphysema and chronic bronchitis that obstructs the airflow in the lungs. Chronic bronchitis is an abnormal lung condition in which chronic irritation of the lining of the bronchi results in swelling of the bronchi and increased mucus production in the lungs. In emphysema, the alveoli and tissues of the lungs are damaged, which causes collapse and obstruction of the bronchial tube. In addition, narrowing the bronchial tube causes the trapping of the air inside the lungs, giving a barrel chest appearance.

What Are the Causes of Emphysema?

• Smoking tobacco or marijuana.

• Air pollution.

• Inhalation of chemical fumes and dust.

• Alpha-1 antitrypsin deficiency (this is a rare lung disorder in which an inherited deficiency of a protein that protects the elastic fibers of the lungs results in alpha-1 antitrypsin deficiency emphysema).

What Are the Risk Factors for Emphysema?

• Smoking - Emphysema most commonly affects smoking individuals. The risk of developing emphysema increases with the increase in tobacco usage and years of smoking.

• Age - Smoking-related emphysema will show symptoms more commonly around the age of 40 to 60.

• Exposure to Second-hand Smoke - People who inhale the smoke from a cigar, pipe, or cigarette of someone else for a long time (secondhand smoke) have an increased risk of emphysema.

• Exposure to Fumes and Dust - Inhaling fumes from burning fuels or dust from cotton, wood, or grains for a long time increases the risk of developing emphysema.

What Are the Symptoms of Emphysema?

• Difficulty in breathing.

• Wheezing.

• Smoker’s cough or long-term cough.

• Fatigue.

• Increased mucus production.

• Whistling sound while breathing.

• Tightness of the chest.

What Are the Different Types of Pulmonary Emphysema?

Pulmonary embolism is classified into three subtypes based on the distribution of the disease within the pulmonary lobules.

• Centriacinar Emphysema:

Centriacinar emphysema is the most commonly found emphysema that appears as an enlarged centriacinar space. It usually affects the second and third respiratory bronchioles. It is often located in the upper part of the lung. Centriacinar emphysema is more common in heavy smokers.

• Panacinar Emphysema:

This is characterized by the even distribution of emphysematous changes inside the secondary lobules. It is divided into localized and diffuse forms. The localized form is characterized by its multilobular distribution, and the localized form is confined to the particular anatomy. The incidence of panacinar emphysema is low as it is caused by alpha-1 antitrypsin deficiency. It is often located in the lower part of the lung.

• Distal Acinar Emphysema:

Distal acinar or paraseptal emphysema has enlarged airspace associated with fibrosis which most commonly occurs on the dorsal surface of the upper part of the lung. This type of emphysema may be found along with other types. Distal acinar emphysema may cause a pneumothorax (a condition in which air or gas is in the cavity between the lungs and the chest wall, causing lung collapse), in adult patients; they are usually asymptomatic.

What Are the Radiological Findings of Emphysema?

Chest Radiography:

• In chest radiography, mild to moderate emphysema appears as a bilateral (both sides) hyperlucent area. Some of the common imaging findings of emphysema are hyperinflated lungs, flattened hemidiaphragm, horizontal ribs, widened costophrenic angles, and narrowed mediastinum. The peripheral vascular markings are more prominent in patients with pulmonary hypertension and right-sided heart failure.

• Juxtaphrenic peak or Kattan sign is the peaked appearance of the hemidiaphragm seen in lobar collapse or after lobectomy surgery.

• The Saber sheath trachea is the coronal narrowing of the intrathoracic part of the trachea associated with the widening of the sagittal diameter in chronic obstructive pulmonary disease.

• Increased anteroposterior diameter and retrosternal space are also seen in chest radiography.

• Chest X-rays can detect only 41 percent of patients with moderate emphysema and two-thirds with severe emphysema. Chest radiographs can not determine the severity of the disease and fail to detect patients with COPD without prominent emphysema.

• The lateral chest X-ray shows increased retrosternal space and a flattened anterior diaphragmatic angle. In pulmonary hypertension, the shadows of the hilar vasculature become more prominent, and due to right ventricular enlargement, the lower retrosternal space is filled with air. Irregular vascular supply to the lungs is also visible.

Computed Tomography (CT):

• High-resolution computed tomography (HRCT) has higher sensitivity and specificity in the diagnosis of emphysema than plain chest radiographs. Unlike chest radiographs (which cannot determine the severity of the disease), HRCT reveals combined emphysema and fibrosis. Furthermore, HRCT can detect mild or subclinical emphysema and differentiate the emphysema types. In addition, a CT scan can predict the outcome of lung surgery.

• Centrilobular emphysema appears as a focal emphysematous space that measures up to one centimeter and is located inside the secondary pulmonary lobule. Sometimes a dot may be found at the center or periphery of the lobule, indicating a central bronchovascular bundle.

• Panlobular emphysema is seen in the lower lobes and is uniformly distributed across the secondary pulmonary lobule.

• Paraseptal emphysema is found near the septal lines and pleura and appears as tiny focal lucencies measuring about 10 mm in size. This is distributed over the periphery of the secondary pulmonary lobule.

Nuclear Imaging:

Xenon-133 lung ventilation scintigraphy is used to evaluate lung function before and after lung volume reduction surgery (LVRS).

Magnetic Resonance Imaging (MRI):

In MRI, hyperpolarized gasses are used as a contrast agent. Contrast agents are inhaled to provide images of the lung spaces. Preoperative dynamic MRI is helpful in selecting patients for LVRS. In addition, diffuse weighted helium MRI is useful for the diagnosis of distal airspace enlargement and associated large and small airway disease.

Conclusion:

High-resolution computed tomography (HRCT) is the standard imaging tool advised for pulmonary emphysema. HRCT can determine the severity of the disease and differentiate the types of emphysema, which are not possible in plain chest radiography. Helical CT can scan the whole chest in a single acquisition which takes less than 20 seconds. Helical CT is superior in diagnosing and quantifying emphysema to pulmonary function tests and plain radiography. Chest radiographs are not able to provide the diagnosis of mild emphysema. Therefore, clinical examination, lung function, and additional images are also considered in such cases. They help differentiate emphysema from lung cancer or superadded infection and detect complications during acute exacerbations.