Emphysema

The following article is provided as a public service of Daniel Powers, M.D.:
B-Reader, Board Certified Diagnostic & Nuclear Radiologist, Certified by the American Board of Radiology

 

Emphysema

Emphysema represents a condition of the lungs characterized by “permanent, abnormal enlargement of air spaces distal to the terminal bronchiole [the area of the pulmonary acinus = the respiratory unit of the lung], accompanied by the destruction of their walls“. Although some have indicated that this definition includes the concept that these changes are “without obvious fibrosis”, the fact is that paracicatricial emphysema, as well as some paraseptal and centrilobular emphysematous changes are associated with fibrosis and thus, that aspect of the definition has been dropped.

There is no universal agreement on what constitutes the most reliable method to assess “abnormal enlargement” of the air spaces distal to the terminal bronchiole and to quantify the “destruction” of their walls. 4 primary types of emphysema are described based upon microscopic/histologic criteria, which is not necessarily that which is seen on imaging studies, and to some extent may be of equivocal value; although, it is helpful in trying to give a general classification to the system. There are in addition to the four main categories, several sub classifications and additional findings associated with emphysema. Emphysema is also graded pathologically as mild, moderate or severe by a panel grading system.

The airways are made up of hollow tubes that conduct air to the lungs. They are lined by pseudostratified, ciliated, columnar epithelium. Cartilage supplies support and prevents collapse. An additional muscle coat and submucosal glands contribute to their structure. Airways are divided into bronchi and bronchioles. The bronchi have cartilage within their walls and the bronchioles do not. The main stem bronchus bifurcates in to the segmental bronchi, which bifurcates into the large subsegmental bronchi, which bifurcate into the small bronchi, which bifurcate into the terminal bronchioles, which bifurcate into acini consisting of respiratory bronchioles, alveolar ducts, alveolar sacs and alveoli. Cartilage within the bronchi becomes sparser towards the periphery, where it is only present at bifurcations and no longer provides the tube rigidity to prevent collapse. A secondary pulmonary lobule contains three to five terminal bronchioles each of which is connected to their respective pulmonary acinus. A pulmonary acinus is the respiratory unit of the lung which is supplied by a terminal bronchiole. These vary in size and shape and may be up to 1 cm in diameter. The pulmonary acinus is composed of tissue distal to the terminal bronchiole compromising three to eight generations of respiratory bronchioles with their associated alveolar ducts, alveolar sacs and accompanying alveoli. Respiratory bronchioles look similar to terminal bronchioles, but have alveoli opening directly into their lumen. Although emphysema is often classified histologically based upon the changes to the pulmonary acinus, radiographically, it is preferred to describe the findings in relationship to the secondary pulmonary lobules (a cluster of 3 to 5 acini).

People with emphysema have obstructive lung disease. This is manifested physiologically by both airflow obstruction and a decrease in diffusion capacity. The air flow obstruction occurs when the airways collapse on expiration due to the destruction of lung parenchyma and loss of airway tethering and support. Loss of diffusion capacity occurs due to the destruction of both the lung tissue and its pulmonary vascular bed.

Chronic Obstructive Pulmonary Disease (COPD), represents chronic irreversible airway destruction secondary to a combination of emphysema and chronic bronchitis. It is a non-specific term. Emphysema is a more specific term and the types and locations of emphysema (centrilobular, paraseptal, panlobular and paracicatricial) are even more specific. Smokers can and often have both chronic bronchitis and emphysema simultaneously.

Chest X-Ray Changes in Emphysema:

The two primary findings are:

  1. Increased Lung Volumes, i.e., hyperaeration or overinflation.
  2. Lung Destruction (bullae or decreased vascularity which gives increased lung lucency and decreased vessel size and presence).

In end-stage disease, emphysema and chronic obstructive pulmonary disease can result in pulmonary arterial hypertension and eventually cor pulmonale (cp) – which causes an increase in the pulmonary arterial size, as well as right ventricular enlargement and cardiomegaly.

    1. Direct Signs:
      1. Bullae with Defined Walls
      2. Irregular Areas of Radiolucency
    1. Indirect Signs:
      1. Hyperaeration: (Increased lung volumes and/or overinflation). This is measured by:
        1. Increased Lung Height: When the measurement of the dome of the right hemi-diaphragm to the tubercle of the first rib measures greater than or equal to 30 cm, this is considered overinflation.
        2. Flattening of the Diaphragm: Measured by drawing a line on the PA view between the costophrenic and cardiophrenic angles and determining whether or not the diaphragm is less than 1.5 cm above that line. If it is, then the diaphragm is flattened. This can also be determined on the lateral view by drawing a line from the anterior costophrenic to the posterior costophrenic angles and likewise determining whether or not the diaphragm is less than (1.5 cm to) 2.7 cm above that line. The cardiophrenic angle can also be called the vertebrophrenic angle and the anterior costophrenic angle on the lateral view can be known as the sternophrenic angle.
        3. Increased Retrosternal Air Space: When the horizontal distance between the posterior margin of the sternum and the anterior margin of the ascending aorta measures greater than 2.5 cm (some say as much as 4.5 cm) in distance and where the horizontal distance is measured 3 cm beneath the angle of Louis (sternomanubrial junction), increased retrosternal air space enlargement is considered.
        4. A Low Position of the Diaphragm: When the dome of the right diaphragm is at or below the anterior end of the right 7th rib, this is considered overinflation.
        5. Air Space Below the Cardiac Contour: Overinflation is associated with visualization of the lungs extending beneath the cardiac silhouette.
        6. Narrowing of the Heart Diameter: A narrow heart width of less than 11.5 cm is often due to overinflation.
        7. Visualized Diaphragmatic Muscle Slips: is a sign of overinflation.
        8. Obtuse Costophrenic Angles: which appear “blunted” are also a result of overinflation.
      1. Alterations in the Vascular Pattern:
        1. Local Avascular/Translucent Areas: caused by destroyed lung tissue from emphysema and bullae formation.
        2. Decreased Peripheral Vascular Markings: given bullae and emphysematous holes – destroyed lung tissue needing a lesser vascular supply.
        3. Distortion of Vessels: straightened, stretched, elongated, curved and pruned in appearance.
        4. Increased Branching Angles: caused by vascular bifurcation about bullae, which are distorting them.

 

      Using 4 categories consisting of flattening of the diaphragms and irregular areas of radiolucency on the PA view, plus an increased retrosternal air space and flattening of the diaphragms on the lateral view, a positive chest x-ray study for emphysema is considered present when 2 of 4 categories are identified.

CT and HRCT Findings in Emphysema:

        Areas of

    emphysema

         are

    more conspicuous on HRCT

         than CT and thus, this technique is utilized more often. HRCT has been shown to look like gross cut specimens. In an autopsy laboratory However,

    CT and HRCT can

        underestimate or

    miss mild emphysema

        , especially when holes are

    less than 5 mm in size

        .
        An alternative way to improve visualization of emphysema is the use of spiral CT with reconstruction of contiguous sections using the

    minimal intensity projection technique

        . A “sliding thin slab technique” is utilized where 1 mm thick slices are obtained across a slab or volume of lung, usually 8-10 mm thick, i.e., 8 to 10 contiguous 1 mm thick slices are obtained. A special reconstruction algorithm is utilized based upon the lowest attenuation values present within the slab and thus, this suppresses visualization of the pulmonary vessels and optimizes visualization of the low attenuation (emphysematous) areas. The greater the number of slices in the slab, the greater the suppression of vessels. It has been shown that 8-10 slices is optimal for this technique, at this time.
        The main CT/HRCT classifications of emphysema are:

     

        1. Centrilobular Emphysema (also known as Proximal Acinar or Centriacinar Emphysema).

          Centrilobular emphysema affects the proximal aspects of the lung acinus — primarily the area of the respiratory bronchioles. It is considered secondary to smoking and predominantly involves the upper lung zones.

          Its CT/HRCT appearance is one of focal areas of low attenuation holes without walls, measuring millimeters to 1 cm in size, also called the “moth-eaten” appearance. Pulmonary vessels can often be seen within the areas of low attenuation. Centrilobular emphysema is most pronounced in the apices, the posterior segments of the upper lung zones, and the superior segments of the lower lung zones and is less frequently also seen in the middle and lower lung zones. With progression, bullae develop, which do have walls, and result in visualized paraseptal emphysema and subpleural bullae. Severe centrilobular emphysema results in confluent holes that look like panlobular emphysema, however, still, some centrilobular disease in the apical areas are often identified and, as opposed to classic panlobular disease, where there is an uneven distribution of confluent bullae. Because the secondary pulmonary lobule contains multiple (3 to 5) acini, centrilobular emphysematous foci are scattered in the lobule and although often appearing centrally located, may not always be.

        1. Paraseptal Emphysema (also known as Distal Acinar Emphysema).

          Paraseptal emphysema affects the distal aspects of the lung acinus — the alveolar ducts and sacs in the lung periphery, with areas of destruction often marginated by the interlobular septa. It is idiopathic and/or secondary to smoking.

          The CT/HRCT appearance is easily recognizable by the emphysematous low attenuation spaces seen adjacent to the pleura and interlobular septa with well-defined walls, having a “saw-tooth” appearance. It can be found in the azygo-esophageal recess, adjacent the superior mediastinal border and along the anterior junctional region. It can cause interlobular septa to become prominent mimicking lymphangitic carcinomatosis on chest x-ray, but is easily separable on CT/HRCT. Coalescence of disease results in subpleural bullae (bu) especially in the apex of the upper lung zone, which can rupture and result in a pneumothorax (px). Although subpleural bullae are commonly associated with paraseptal emphysema, they are seen in all types of emphysema including as an isolated phenomenon unrelated to emphysema. Apical subpleural bullae are present in 80-90% of patients with spontaneous pneumothorax.

          Paraseptal emphysema is differentiated from honeycombing in that it often forms a single row adjacent the chest wall, is most severe in the apices, and can have holes (often improperly called “cystic” changes) greater than 1 cm in diameter. Honeycombing often forms multiple rows, is most severe at the lung bases, and usually has holes (“cystic” spaces) less than 1 cm in diameter.

        1. Panlobular Emphysema (also known as Panacinar Emphysema).

          Panlobular emphysema affects all components of the lung acinus and involves the entire secondary pulmonary lobule (3 to 5 acini). It is most frequently secondary to alpha-1-anti-trypsin deficiency (also called alpha-1-protease inhibitor deficiency). It is classically considered the emphysema of non-smokers. It can also occur however, in elderly individuals with distal to bronchiole and bronchiolar obliteration, in IV drug addicts with talcosis, in patients with Swyer/James (MacLeod’s) Syndrome and even in smokers.

          This has lower lung zone predominance, greatest in the left lower lung zone. There are widespread areas of abnormal low attenuation areas with decreased vascularity. Thus, it can be easily overlooked, since it is diffuse and lacking juxtaposed contrasting densities. The left lower lung zone is more involved than the middle and upper lung zones. Patterns of panlobular and centrilobular emphysema frequently co-exist in the same individual. Usually with alpha-1-anti-trypsin deficiency, there is greater loss of lung caused by infection than seen in the general population and these patients can develop bronchiectasis and bronchial wall thickening. Bullae are less frequent in this type of emphysema, compared to other types.

        1. Paracicatricial Emphysema (also know as Cicatricial or Irregular Emphysema).

          This is emphysema is most frequently associated with patients having complicated type pneumoconioses withprogressive massive fibrosis (PMF), but can also occur adjacent to a localized parenchymal scar, in diffuse pulmonary fibrosis or after an episode of pneumonia. It can also be called Irregular Air Space Enlargement. It isnot localizable to a specific site in the acinus and is associated with fibrosis.

    Other Sub-Categories of Emphysema

        :

        1. Bullous Emphysema (also known as Bullous Lung Disease):

          Bullous emphysema is so named when there are multiple large bullae associated with a compromise in pulmonary function. It is usually associated with concomitant emphysema, although occasionally, it can be familial (thus, the designation of “Bullous Lung Disease” rather than Bullous Emphysema”).

          Bullae are thin-walled, sharply-demarcated areas of lung destruction with avascularity, measuring 1 cm or more in diameter, with thin walls measuring less than 1 mm in thickness. The bullae are commonly subpleural in location and can occur in any of the 4 types of emphysema, but most commonly in the centrilobular and paraseptal types. The bullous lesion can be uni or multi-locular with a septated space. When looking at an autopsy removed lung, a bullous lesion can be seen as a localized empty sac or bag-like protrusion from the lung surface. They are most commonly subpleural in location. Bullae can be associated with pneumothorax formation, infection and/or hemorrhage. They can occasionally disappear, especially after infection or hemorrhage, or even on a spontaneous basis.

          Bullous Emphysema has three types:

          1. Subpleural Type: These subpleural bullae contain only gas with no alveolar remnants or blood vessels. They are often located in the apex of the upper lung zone, and along the costophrenic rim of the middle lobe and lingua, but may be seen in the vicinity of parenchymal scars.
          2. Superficial Type: These bullae are found along the anterior edge of the upper and/or middle lung zones, or lingula, and over the diaphragms. They contains blood vessels and strands of partially-destroyed lung.
          3. Deep Type: These bullae are found within the lung substance and contain strands of partially-destroyed lung tissue and blood vessels.

     

        1. Giant Bullous Emphysema: (“Vanishing Lung Syndrome” or “Primary Bullous Disease of the Lungs”)

          It is usually associated with young males who show large progressive upper lung zone bullae that are often asymmetric. The giant bullous lesions occupy greater than or equal to one-third of the hemithorax. Oftentimes, the adjacent normal lung is compressed, becoming atelectatic, making it difficult for that portion of the lung to appropriately function. Spontaneous pneumothorax is a common consequence of this disease. Other etiologies for Vanishing Lung Syndrome include pulmonary sarcoid or Langerhans cell hystiocytosis.

        1. Focal Dust Emphysema (also known as Focal Emphysema in Silicosis).

          This is focal emphysema surrounding silicotic nodules.

        1. Congenital Lobar Emphysema (CLE)

          CLE usually presents in the first month of life associated with respiratory distress. There is marked overinflation of a lobe - left upper > right middle > right upper lobes. Lower lobe involvement is rare. There is often mediastinal shift away from the overinflated lobe. The etiology is usually but not always a partial or complete bronchial obstruction from such causes as deficient cartilage within the bronchus, an extrinsic compression such as by an anomalous vessel or bronchogenic cyst or a problem involving the lumen itself such as a mucosal fold. There is overinflation and air trapping resulting in a hyperlucent lung although retained fetal lung fluid can leave it looking opaque. Resection of the abnormal lobe is often required.

        1. Interstitial Emphysema

          Air can escape the lungs through injury to and rupture of the alveoli (barotrauma) when mechanical ventilationoccurs. Air collects dissects into the interstitium as collections of perivascular air or a air bubbles within areas of consolidation, which is seen on CT/HRCT but not usually on chest x-rays. This air continues to dissect and make its way into the mediastinum causing a pneumomediastinum (visible on chest x-ray) and can also continue into the subcutaneous soft tissues of the chest wall as subcutaneous emphysema.

    My Training and Acknowledgements

        :
        The above diagrams and article are based upon my education and training, multiple peer review journal articles and textbooks, as well as lectures.
        My initial training for chest disease was at L.A. County/USC Medical Center. In private practice, I self-studied and passed the Federal B-Reader Certification testing in 1984 and re-certified every four years thereafter. I also independently tutored with Dr. Gordon Gamsu at the University of California at San Francisco, when he was first publishing his articles on the CT and HRCT findings in pneumoconioses. Based upon his training and my understanding of his information, I began performing large-scale CT/HRCT imaging studies utilizing terminology learned through him and from various course lectures, journal articles and textbooks. Multiple other authors and educators have contributed to my understanding as have their lectures, articles and textbook chapters. Recent experiences have included the latest American College of Radiology Symposium on Radiology of the Pneumoconioses, presented between March 5-8, 2004, and re-certification as a Federal Government “B-Reader” during that same period. Also included in the review were the “Guidelines for the Use of the ILO International Classification of Radiographs of Pneumoconiosis”, Revised Edition 2000, booklet #22 from the International Labor Office in Geneva. I also attended the Radiological Society of North America’s 90th Scientific Assembly and Annual Meeting, November 28 – December 3, 2004 and Chest Imaging for the Clinician and Radiologist, 2005, presented by the American College of Chest Physicians, June 10 – 12, 2005, in which multiple lecturers contributed information including Theresa McCloud, M.D., David P. Naidich, M.D., and W. Richard Webb, M.D. There was a syllabus with that course. Other texts utilized included The CIBA Collection of Medical Illustrations, Volume 7, Respiratory System, illustrated by Frank Netter, M.D. (1979); Diseases of the Lung, Radiologic and Pathologic Correlations, by Muller, Fraser, Lee and Johkoh, published by Lippincott, Williams, and Wilkins, in 2003; Thoracic Imaging, by W. Richard Webb and Charles B. Wiggins, published by Lippincott, Williams and Wilkins, in 2005; and the Fourth Edition, Imaging of Diseases of the Chest, by Hansel, Armstrong, Lynch and McAdams, published by Elsevier Mosby, in 2005. Additional anatomic texts included, Clinically Oriented Anatomy, Fourth Edition by Moore and Dalley, published by Lippincott, Williams and Wilkins in 1999 and Chest Atlas, Radiographically Correlated Thin-Section Anatomy in Five Planes by Littleton and Durizch, published by Springer-Verlag in 1994. Special thanks to Hide Konishi who worked with me on making the visual diagrams come into reality on Adobe Illustrator

    ®

         and Bill Malin who completed the web presentation.

    My Thoughts and Wisdom

        :
        Medicine is an “art” based upon “science.” We as educators and clinicians are constantly learning and updating our teachings and knowledge base. Certainly, by my presentation, I have added addition “art” (the visual diagrams) to this science with the hope that it will help further clarify the learner’s understanding of what Radiologists look for when observing emphysema.
        Unfortunately, many authors use individualized coined terms, many of which overlap and some with the same name, that mean different things to different people. There is no easy fix. I have tried to standardize the language.
        Regarding

    measurements and statistics

         - It must be remembered that

    common sense must prevail

         when using numbers and that there are

    false positive (overcalls)

         and

    false negatives (undercalls)

        , plus there are

    always exceptions to the rules

        . There is no absolutely correct statistic, since involved study groups and technology change and individual patients have their own select responses to insults. The quoted statistics are

    for understanding general concepts only

        . The bottom line is, that imaging studies are part of the Sherlock Holmes investigation of a patient’s disease – identifying if the anatomy is normal or abnormal and trying to direct one to a specific diagnosis when possible. Classifications of emphysema visually overlap both visually and in terms of originating insult and thus, the significance and type of emphysema observed is made based upon the patient’s history including whether he or she smoked, the clinical examination, pulmonary function testing and imaging findings, taken all together.
        If you detect any errors, have additional information to point me to, use other useful terms or have comments please do e-mail them to me at danielpowers@earthlink.net.
        Thank you.
        Daniel Powers, M.D.

     

        Diagnostic Radiologist

     

        American Board of Radiology Certified

     

      Federal Government Certified “B-Reader”

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