Pulmonary emphysema is defined as the "abnormal permanent enlargement of the airspaces distal to the terminal bronchioles accompanied by destruction of the alveolar wall and without obvious fibrosis". Emphysema is one of the entities grouped together as chronic obstructive pulmonary disease. Emphysema is best evaluated on CT, although indirect signs can be noticed on conventional radiography in a proportion of cases. This article focuses on panlobular emphysema, paraseptal emphysema, and in particular centrilobular emphysema.
At the time of initial writing, approximately 210 million people are affected worldwide leading to 3 million deaths annually 1. It is predominantly a disease of middle to late life owing to the cumulative effect of smoking and other environmental risk factors. It traditionally affected more men than women but with increased smoking and environmental risk factor exposure among women, the incidence is now equal between the sexes. Patients with genetic risk factors such as alpha-1-antitrypsin deficiency may present earlier according to phenotype.
- smoking: by far the most common
- alpha-1-antitrypsin (AAT) deficiency
- intravenous injection of methylphenidate (Ritalin lung)
The clinical features of emphysema should be distinguished from the signs and symptoms of chronic bronchitis. Patients with emphysema are hypocapnoeic and are often referred to as "pink puffers". This compares with the hypercapnoea and cyanosis of chronic bronchitis with patients referred to as "blue bloaters". In practice, features of these two syndromes coexist as chronic obstructive pulmonary disease.
Patients typically report dyspnoea without significant sputum production.
Signs of emphysema include:
- absence of cyanosis
- pursed-lip breathing
- chest hyperinflation
- reduced breath sounds
- hyper-resonant to percussion
- cor pulmonale (late)
Emphysema is one of a heterogeneous group of pathological processes forming chronic obstructive pulmonary disease, and is itself a relatively vague term encompassing a number of entities and morphological patterns including:
- morphologic subtypes
- idiopathic giant bullous emphysema (or vanishing lung syndrome)
- congenital lobar emphysema
- pulmonary interstitial emphysema
The three morphologic subtypes of emphysema are named according to their relationship to the secondary pulmonary lobule.
Centrilobular emphysema is the most frequently encountered type and affects the proximal respiratory bronchioles, particularly of the upper zones. It is strongly associated with smoking in a dose-dependent way 3. Rarely, severe centrilobular emphysema can be seen in the bases in patients with Salla disease 4.
Panlobular emphysema in contrast, affects the entire secondary pulmonary lobule and is more pronounced in the lower zones, matching areas of maximal blood flow. It is seen particularly in alpha-1-antitrypsin (AAT) deficiency (exacerbated by smoking) 2-4, intravenous injection of methylphenidate (Ritalin lung) 3 or Swyer-James syndrome 4.
Paraseptal emphysema affects the peripheral parts of the secondary pulmonary lobule, and is usually located adjacent to the pleural surfaces (including pleural fissures) 3. It is also associated with smoking, and can lead to the formation of subpleural bullae and spontaneous pneumothorax 3.
Except in the case of very advanced disease with bulla formation, chest radiography does not image emphysema directly, but rather infers the diagnosis due to associated features 2-3:
- paucity of blood vessels, often distorted
pulmonary arterial hypertension
- pruning of peripheral vessels
- increased calibre of central arteries
- right ventricular enlargement
It should be remembered, however, that the most common plain film appearance of COPD is "normal" and the role of chest radiography is to eliminate other causes of lung symptoms such as infection, bronchiectasis or cancer 6.
CT is currently the modality of choice for detecting emphysema; HRCT is particularly effective. It should be noted, however, that there is relatively poor correlation between autopsy-proven emphysema, pulmonary function test abnormalities and CT with 20% of pathology-proven cases not being evident on CT and 40% of patients with abnormal CT having normal pulmonary function tests.
CT is able to discriminate between centrilobular, panlobular, and paraseptal emphysema.
Centrilobular is by far the most common type encountered, and is a common finding in asymptomatic elderly patients. It is predominantly located in the upper zones of each lobe (i.e. apical and posterior segments of the upper lobes, and superior segment of the lower lobes) and has a patchy distribution 4. It appears as focal lucencies (emphysematous spaces) which measure up to 1 cm in diameter, located centrally within the secondary pulmonary lobule, often with a central or peripheral dot representing the central bronchovascular bundle 2-4.
Panlobular emphysema is predominantly located in the lower lobes, has a uniform distribution across parts of the secondary pulmonary lobule, which are homogeneously reduced in attenuation 2-4.
Paraseptal emphysema is located adjacent to the pleura and septal lines with a peripheral distribution within the secondary pulmonary lobule. The affected lobules are almost always subpleural, and demonstrate small focal lucencies up to 10 mm in size.
In all three subtypes, the emphysematous spaces are not bounded by any visible wall 3.
MRI is in the research phases for evaluation of lung parenchymal abnormalities like emphysema. Dynamic breathing MRI may have a future role in assessing pulmonary emphysema.5
Treatment and prognosis
Unfortunately, once lung tissue is lost, no regrowth occurs. Treatment is therefore supportive and aimed at preserving remaining lung parenchyma. Interventions include:
- smoking cessation
- oxygen therapy (in chronic hypoxaemia)
- symptom and exacerbation control
- short and long-acting beta-2 agonists
- inhaled anticholinergics
- inhaled glucocorticoids
- pulmonary rehabilitation
In patients with severe bullous change with resultant compression of remaning normal lung parenchyma, lung volume reduction therapy may be considered in selected patients.
Lung transplantation is considered in cases of alpha-1-antitrypsin deficiency.
Prognosis is worse in patients who continue to smoke, are alpha-1-antitrypsin deficient, have low FEV1 at time of diagnosis, or have other comorbidities (e.g. heart failure, respiratory failure, frequent exacerbations).
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