Images in Allergy The Role of Computed Tomography in Chronic Obstructive Pulmonary Diseases Thaddeus F.-C. Sze, MDa,*, Matthew G. Ditzler, MDa,*, Eric M. Walser, MDa, and William J. Calhoun, MDb Galveston, Texas
CHRONIC OBSTRUCTIVE PULMONARY DISEASE Chronic obstructive pulmonary disease (COPD) is a collective term applied to include various disorders that lead to airflow limitation as measured by reduction in the ratio of FEV1 to forced vital capacity, and includes emphysema, chronic bronchitis, and bronchiectasis. The clinical, physiologic, and immunologic presentation of COPD is described elsewhere in this issue, and causative factors delineated. For the clinician, evaluation using an imaging tools is critical for proper diagnosis and management.
Clinicians should also have basic familiarity with the radiation exposure produced by different CT studies. The radiologist will attempt to maximize CT sensitivity while minimizing the unnecessary dose. For example, a study optimized for the detection of small pulmonary emboli by using 1.25-mm slices will deliver 4 times the radiation of a standard 5-mm CT slice, but if the detection of nodules larger than approximately 10 mm is the purpose, the extra dose will be unnecessary. A detailed description of the clinical query being posed by the examination should be communicated to the radiologist to maximize the value of the examination to the patient and providers.
COMPUTED TOMOGRAPHY Chest computed tomography (CT) is a standard method for imaging the lungs. Important technical variables in CT imaging include the presence or absence of vascular contrast material, slice thickness, slice contiguity, X-ray beam energetics and dose, and other technical factors. Aside from the first, these factors are largely controlled by the radiologist, depending on the diagnostic information that is sought. However, some knowledge of these factors, and close communication with the radiologist, is critical to ensure that the optimal study is performed. The most important of these elements are the need for contrast and an awareness of radiation dose. Most evaluations of the lung parenchyma do not require intravenous contrast because sufficient contrast is afforded by airfilled lung-surrounding lesions of interest; studies described here have not required contrast. Therefore, the risks of contrast administration such as nephrotoxicity can be avoided, which is advantageous for patients with complex conditions and multiple medications. Contrast becomes important to distinguish structures of similar density. In the chest, contrast is most frequently needed to evaluate the mediastinum and hila, and to distinguish vascular and lymphatic structures.
APPROACH TO THE NORMAL CHEST CT SCAN Although CT of the chest provides other information, for the purposes of this discussion, we will focus on the parenchyma. A lung window (Figure 1, A-D) is the optimal viewing mode. The fissures and lobular septa are thin; bronchi and vessels taper with increasing distance from the mediastinum. Normally, an airway and its accompanying vasculature will be of roughly the same caliber. The air spaces should be uniformly dark, but not entirely devoid of character. Unexpected opacity or lucency within the airspaces, or unexpected changes in caliber of septa, vessels, or bronchi, may be abnormal. Normal findings (Figure 1) are the most common outcome of CT examination in asthma.
a
Division of Pulmonary and Critical Care, Department of Radiology, University of Texas Medical Branch, Galveston, Texas b Division of Allergy and Clinical Immunology, Department of Internal Medicine, University of Texas Medical Branch, Galveston, Texas Conflicts of interest: W. J. Calhoun has received consultancy fees from Genentech; is employed by the University of Texas Medical Branch; and has received research support from Federal Emergency Management Agency. The rest of the authors declare that they have no relevant conflicts of interest. Received for publication February 27, 2015; revised April 28, 2015; accepted for publication May 1, 2015. Corresponding author: William J. Calhoun, MD, Department of Internal Medicine, 4.116 John Sealy Annex, 300 University Blvd, Galveston, TX 77555. E-mail: [email protected]. * These authors contributed equally to this work. J Allergy Clin Immunol Pract 2015;3:594-6. 2213-2198 Ó 2015 American Academy of Allergy, Asthma & Immunology http://dx.doi.org/10.1016/j.jaip.2015.05.018
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CHEST CT IN EMPHYSEMA Emphysema can manifest a number of patterns, depending on the etiology (Figure 2). Smoking-related emphysema classically presents with a centrilobular pattern, with multiple areas of low attenuation (dark, air-filled voids), favoring the upper lobes and centered in secondary pulmonary lobules. With milder emphysema, these regions can appear separate, but with increasing severity, they may form bullae, becoming confluent with one another. CHEST CT IN CHRONIC BRONCHITIS Chronic bronchitis is characterized by a persistent productive cough. Specific imaging criteria do not exist, and CT findings, if present, may support an underlying diagnosis. In smokers, findings tend to overlap with that of centrilobular emphysema. Bronchial wall thickening and mucus in the tracheobronchial tree can be seen in addition to small airway abnormalities. Expiratory-phase scans in patients with small airway disease can manifest mosaic attenuation, caused by air trapping, and characterized by intermixed areas of lower and higher attenuation (Figure 3). CHEST CT IN BRONCHIECTASIS Bronchiectasis refers to an irreversible dilatation of the bronchial tree, typically involving the larger, cartilagenous airways, and is commonly associated with bronchial wall thickening.
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IMAGES IN ALLERGY
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FIGURE 1. Normal CT of the chest: apex (A), mid-great vessels (B), carina (C), diaphragm (D).
FIGURE 2. CT in emphysema demonstrating apical (A) and mid-field (B) hypodensities (arrows), and bullae (chevrons).
FIGURE 3. CT in chronic bronchitis. Note thickened airway walls (A, chevron), mucus in airways (B, arrow), and mosaic pattern due to uneven air trapping on expiratory scan (lower panel, C).
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FIGURE 4. CT in bronchiectasis. Note enlarged, nontapering airways (A and B, right lung, chevrons) and bronchoarterial ratio of more than 1 (A and B, central vessels). There is associated bulla formation (B, right lung, arrow). Exaggerated cystic or varicose bronchiectasis can be seen in conditions such as allergic bronchopulmonary aspergillosis (C, hollow arrows).
Congenital diseases, infections, and toxic inhalations, among other factors, can cause bronchiectasis. CT findings of bronchiectasis include a dilation of the airway caliber resulting in an increased bronchoarterial ratio of more than 1. Bronchiectatic airways demonstrate a lack of normal tapering and remain dilated (Figure 4, A and B). Nonspecific findings associated with bronchiectasis include bronchial wall thickening, mucus within the tracheobronchial tree, and mosaic pattern with air trapping.
SUMMARY AND CLINICAL IMPLICATIONS Imaging the chest using CT is an essential part of the evaluation of patients with COPDs. In addition to anatomic information regarding alveolar tissue destruction and airway wall thickening, the CT is useful in identifying and monitoring lung nodules that may exist as comorbidities in patients with COPD. Most patients with COPD will benefit from CT evaluation of their lungs.
CHRONIC OBSTRUCTIVE PULMONARY DISEASE Chronic obstructive pulmonary disease (COPD) is a collective term applied to include various disorders that lead to airflow limitation as measured by reduction in the ratio of FEV1 to forced vital capacity, and includes emphysema, chronic bronchitis, and bronchiectasis. The clinical, physiologic, and immunologic presentation of COPD is described elsewhere in this issue, and causative factors delineated. For the clinician, evaluation using an imaging tools is critical for proper diagnosis and management.
Clinicians should also have basic familiarity with the radiation exposure produced by different CT studies. The radiologist will attempt to maximize CT sensitivity while minimizing the unnecessary dose. For example, a study optimized for the detection of small pulmonary emboli by using 1.25-mm slices will deliver 4 times the radiation of a standard 5-mm CT slice, but if the detection of nodules larger than approximately 10 mm is the purpose, the extra dose will be unnecessary. A detailed description of the clinical query being posed by the examination should be communicated to the radiologist to maximize the value of the examination to the patient and providers.
COMPUTED TOMOGRAPHY Chest computed tomography (CT) is a standard method for imaging the lungs. Important technical variables in CT imaging include the presence or absence of vascular contrast material, slice thickness, slice contiguity, X-ray beam energetics and dose, and other technical factors. Aside from the first, these factors are largely controlled by the radiologist, depending on the diagnostic information that is sought. However, some knowledge of these factors, and close communication with the radiologist, is critical to ensure that the optimal study is performed. The most important of these elements are the need for contrast and an awareness of radiation dose. Most evaluations of the lung parenchyma do not require intravenous contrast because sufficient contrast is afforded by airfilled lung-surrounding lesions of interest; studies described here have not required contrast. Therefore, the risks of contrast administration such as nephrotoxicity can be avoided, which is advantageous for patients with complex conditions and multiple medications. Contrast becomes important to distinguish structures of similar density. In the chest, contrast is most frequently needed to evaluate the mediastinum and hila, and to distinguish vascular and lymphatic structures.
APPROACH TO THE NORMAL CHEST CT SCAN Although CT of the chest provides other information, for the purposes of this discussion, we will focus on the parenchyma. A lung window (Figure 1, A-D) is the optimal viewing mode. The fissures and lobular septa are thin; bronchi and vessels taper with increasing distance from the mediastinum. Normally, an airway and its accompanying vasculature will be of roughly the same caliber. The air spaces should be uniformly dark, but not entirely devoid of character. Unexpected opacity or lucency within the airspaces, or unexpected changes in caliber of septa, vessels, or bronchi, may be abnormal. Normal findings (Figure 1) are the most common outcome of CT examination in asthma.
a
Division of Pulmonary and Critical Care, Department of Radiology, University of Texas Medical Branch, Galveston, Texas b Division of Allergy and Clinical Immunology, Department of Internal Medicine, University of Texas Medical Branch, Galveston, Texas Conflicts of interest: W. J. Calhoun has received consultancy fees from Genentech; is employed by the University of Texas Medical Branch; and has received research support from Federal Emergency Management Agency. The rest of the authors declare that they have no relevant conflicts of interest. Received for publication February 27, 2015; revised April 28, 2015; accepted for publication May 1, 2015. Corresponding author: William J. Calhoun, MD, Department of Internal Medicine, 4.116 John Sealy Annex, 300 University Blvd, Galveston, TX 77555. E-mail: [email protected]. * These authors contributed equally to this work. J Allergy Clin Immunol Pract 2015;3:594-6. 2213-2198 Ó 2015 American Academy of Allergy, Asthma & Immunology http://dx.doi.org/10.1016/j.jaip.2015.05.018
594
CHEST CT IN EMPHYSEMA Emphysema can manifest a number of patterns, depending on the etiology (Figure 2). Smoking-related emphysema classically presents with a centrilobular pattern, with multiple areas of low attenuation (dark, air-filled voids), favoring the upper lobes and centered in secondary pulmonary lobules. With milder emphysema, these regions can appear separate, but with increasing severity, they may form bullae, becoming confluent with one another. CHEST CT IN CHRONIC BRONCHITIS Chronic bronchitis is characterized by a persistent productive cough. Specific imaging criteria do not exist, and CT findings, if present, may support an underlying diagnosis. In smokers, findings tend to overlap with that of centrilobular emphysema. Bronchial wall thickening and mucus in the tracheobronchial tree can be seen in addition to small airway abnormalities. Expiratory-phase scans in patients with small airway disease can manifest mosaic attenuation, caused by air trapping, and characterized by intermixed areas of lower and higher attenuation (Figure 3). CHEST CT IN BRONCHIECTASIS Bronchiectasis refers to an irreversible dilatation of the bronchial tree, typically involving the larger, cartilagenous airways, and is commonly associated with bronchial wall thickening.
J ALLERGY CLIN IMMUNOL PRACT VOLUME 3, NUMBER 4
IMAGES IN ALLERGY
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FIGURE 1. Normal CT of the chest: apex (A), mid-great vessels (B), carina (C), diaphragm (D).
FIGURE 2. CT in emphysema demonstrating apical (A) and mid-field (B) hypodensities (arrows), and bullae (chevrons).
FIGURE 3. CT in chronic bronchitis. Note thickened airway walls (A, chevron), mucus in airways (B, arrow), and mosaic pattern due to uneven air trapping on expiratory scan (lower panel, C).
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FIGURE 4. CT in bronchiectasis. Note enlarged, nontapering airways (A and B, right lung, chevrons) and bronchoarterial ratio of more than 1 (A and B, central vessels). There is associated bulla formation (B, right lung, arrow). Exaggerated cystic or varicose bronchiectasis can be seen in conditions such as allergic bronchopulmonary aspergillosis (C, hollow arrows).
Congenital diseases, infections, and toxic inhalations, among other factors, can cause bronchiectasis. CT findings of bronchiectasis include a dilation of the airway caliber resulting in an increased bronchoarterial ratio of more than 1. Bronchiectatic airways demonstrate a lack of normal tapering and remain dilated (Figure 4, A and B). Nonspecific findings associated with bronchiectasis include bronchial wall thickening, mucus within the tracheobronchial tree, and mosaic pattern with air trapping.
SUMMARY AND CLINICAL IMPLICATIONS Imaging the chest using CT is an essential part of the evaluation of patients with COPDs. In addition to anatomic information regarding alveolar tissue destruction and airway wall thickening, the CT is useful in identifying and monitoring lung nodules that may exist as comorbidities in patients with COPD. Most patients with COPD will benefit from CT evaluation of their lungs.
