Commonly Missed Findings on Chest Radiographs
2022; Elsevier BV; Volume: 163; Issue: 3 Linguagem: Inglês
10.1016/j.chest.2022.10.039
ISSN1931-3543
AutoresWarren B. Gefter, Benjamin A. Post, Hiroto Hatabu,
Tópico(s)Advanced X-ray and CT Imaging
ResumoChest radiography (CXR) continues to be the most frequently performed imaging examination worldwide, yet it remains prone to frequent errors in interpretation. These pose potential adverse consequences to patients and are a leading motivation for medical malpractice lawsuits. Commonly missed CXR findings and the principal causes of these errors are reviewed and illustrated. Perceptual errors are the predominant source of these missed findings. The medicolegal implications of such errors are explained. Awareness of commonly missed CXR findings, their causes, and their consequences are important in developing approaches to reduce and mitigate these errors. Chest radiography (CXR) continues to be the most frequently performed imaging examination worldwide, yet it remains prone to frequent errors in interpretation. These pose potential adverse consequences to patients and are a leading motivation for medical malpractice lawsuits. Commonly missed CXR findings and the principal causes of these errors are reviewed and illustrated. Perceptual errors are the predominant source of these missed findings. The medicolegal implications of such errors are explained. Awareness of commonly missed CXR findings, their causes, and their consequences are important in developing approaches to reduce and mitigate these errors. To err is human . . . —Alexander Pope Chest radiography (CXR) is the most frequently ordered and performed imaging examination worldwide,1Calli E. Sogancioglu E. van Ginneken B. van Leeuwen K.G. Murphy K. Deep learning for chest X-ray analysis: a survey.Medical Image Analysis. 2021; 72102125Abstract Full Text Full Text PDF PubMed Scopus (102) Google Scholar despite its limitations and the availability of more advanced, cross-sectional chest imaging. The clinical usefulness of the CXR is based on its wide availability, cost-effectiveness, ability to depict a broad range of cardiopulmonary conditions,2Raoof S. Feigin D. Sung A. et al.Interpretation of plain chest roentgenogram.Chest. 2012; 141: 545-558Abstract Full Text Full Text PDF PubMed Scopus (105) Google Scholar and low radiation dose. It is performed frequently as the first imaging study in the evaluation of patients with pulmonary symptoms. Despite its widespread clinical usefulness, CXR interpretation remains highly challenging. It is a two-dimensional projection of a three-dimensional volume, with consequent superimposition of structures. Abnormal lung findings often are subtle and nonspecific. The appearance of normal anatomic structures varies with patient age. Chest radiography interpretation thus is appreciably prone to errors. Some of these errors, such as missed lung nodules resulting from early stage lung cancer or a pneumothorax requiring urgent attention, may lead to patient harm. Errors of these types are a common cause of medical malpractice claims. Clinicians therefore must remain proficient in interpreting these studies.3Waite S. Scott J. Gale B. et al.Interpretive error in radiology.AJR Am J Roentgenol. 2017; 208: 1-11Crossref PubMed Scopus (125) Google Scholar,4Brady A. Laoide R.O. McCarthy P. McDermott R. Discrepancy and error in radiology: concepts, causes and consequences.Ulster Med J. 2012; 81: 3-9PubMed Google Scholar This special features article discusses and provides examples of commonly missed CXR findings of clinical significance. The incidence, principal causes, and potential adverse consequences of these errors are explained, including their medicolegal implications. Awareness of these missed findings and their sources are important in developing approaches to avoiding them. Looking at radiologic error as a whole, approximately 1 billion radiologic imaging examinations are performed annually worldwide. The prevalence of radiologist errors has been estimated at 4% in a typical sample of cases encountered in practice, in which a substantial percentage of normal exists.5Bruno M.A. Walker E.A. Abujudeh H.H. Understanding and confronting our mistakes: the epidemiology of error in radiology and strategies for error reduction.Radio Graphics. 2015; 35: 1668-1676Google Scholar,6Garland L.H. On the scientific evaluation of diagnostic procedures.Radiology. 1949; 52: 309-328Crossref PubMed Scopus (164) Google Scholar However, the incidence of errors may be as high as 30% when the test cases all show abnormalities.6Garland L.H. On the scientific evaluation of diagnostic procedures.Radiology. 1949; 52: 309-328Crossref PubMed Scopus (164) Google Scholar, 7Berlin L. Radiologic errors and malpractice: a blurry distinction.AJR Am J Roentgenol. 2007; 189: 517-522Crossref PubMed Scopus (81) Google Scholar, 8Berlin L. Accuracy of diagnostic procedures: has it improved over the past five decades?.AJR Am J Roentgenol. 2007; 188: 1173-1178Crossref PubMed Scopus (107) Google Scholar Garland's6Garland L.H. On the scientific evaluation of diagnostic procedures.Radiology. 1949; 52: 309-328Crossref PubMed Scopus (164) Google Scholar seminal and prolific studies of radiologic error between the late 1940s and late 1950s showed that even experienced radiologists failed to note significant findings on 30% of CXR images showing positive results for disease.5Bruno M.A. Walker E.A. Abujudeh H.H. Understanding and confronting our mistakes: the epidemiology of error in radiology and strategies for error reduction.Radio Graphics. 2015; 35: 1668-1676Google Scholar He also found a false-positive rate of 2%. Many subsequent studies continue to confirm Garland's findings. The interobserver variability in CXR interpretations also is substantial,9Quekel L.G. Kessels A.G. Goei R. van Engelshoven J.M. Detection of lung cancer on the chest radiograph: a study on observer performance.Eur J Radiol. 2001; 39: 111-116Abstract Full Text Full Text PDF PubMed Scopus (29) Google Scholar, 10Balabanova Y. Coker R. Fedorin I. et al.Variability in interpretation of chest radiographs among Russian clinicians and implications for screening programmes: observational study.BMJ. 2005; 331: 379-382Crossref PubMed Scopus (58) Google Scholar, 11Young M. Interobserver variability in the interpretation of chest roentgenograms of patients with possible pneumonia.Arch Intern Med. 1994; 154: 2729Crossref PubMed Scopus (96) Google Scholar generally reported to be 20% among patients with findings,5Bruno M.A. Walker E.A. Abujudeh H.H. Understanding and confronting our mistakes: the epidemiology of error in radiology and strategies for error reduction.Radio Graphics. 2015; 35: 1668-1676Google Scholar with radiologists' disagreement as high as 56%.12Herman P.G. Gerson D.E. Hessel S.J. et al.Disagreement in chest roentgen interpretation.Chest. 1975; 68: 278-282Abstract Full Text Full Text PDF PubMed Scopus (99) Google Scholar This further reflects the challenges of accurate detection of CXR abnormalities, even among experienced observers. Published statistics on the frequency of specific missed CXR findings are limited and largely are based on malpractice data.13Baker S.R. Patel R.H. Yang L. Lelkes V.M. Castro III, A. Malpractice suits in chest radiology: an evaluation of the histories of 8265 radiologists.J Thorac Imaging. 2013; 28: 388-391Crossref PubMed Scopus (30) Google Scholar Missed nodules resulting from lung cancer are the predominant cause for malpractice claims involving chest imaging, accounting for 43%.13Baker S.R. Patel R.H. Yang L. Lelkes V.M. Castro III, A. Malpractice suits in chest radiology: an evaluation of the histories of 8265 radiologists.J Thorac Imaging. 2013; 28: 388-391Crossref PubMed Scopus (30) Google Scholar As detailed further herein, these errors overwhelmingly result from failure to detect the lesions on CXR. Among the most frequent CXR errors, in addition to missed lung nodules or lung cancer, are airspace opacities resulting from pneumonia, pneumothorax, pleural effusion, mediastinal and hilar masses, lymphadenopathy, thoracic fractures, and pneumoperitoneum.13Baker S.R. Patel R.H. Yang L. Lelkes V.M. Castro III, A. Malpractice suits in chest radiology: an evaluation of the histories of 8265 radiologists.J Thorac Imaging. 2013; 28: 388-391Crossref PubMed Scopus (30) Google Scholar As discussed in detail herein, radiologic error can be broken down into two fairly broad categories: perceptual error and cognitive error.14Donald J.J. Barnard S.A. Common pattern in 558 diagnostic radiology errors.J Med Imaging Radiat Oncol. 2012; 56: 173-178Crossref PubMed Scopus (105) Google Scholar Briefly, perceptual error refers to an abnormality being seen retrospectively after having been missed during the initial interpretation of imaging. Cognitive error, however, refers to an abnormality that is detected, but is not understood or is diagnosed incorrectly. Perceptual error is a much more common occurrence, accounting for 60% to 80% of all radiologic errors.3Waite S. Scott J. Gale B. et al.Interpretive error in radiology.AJR Am J Roentgenol. 2017; 208: 1-11Crossref PubMed Scopus (125) Google Scholar,5Bruno M.A. Walker E.A. Abujudeh H.H. Understanding and confronting our mistakes: the epidemiology of error in radiology and strategies for error reduction.Radio Graphics. 2015; 35: 1668-1676Google Scholar It is this perceptual error, or observer error, that seems to account for the high frequency of missed abnormalities on CXR images, specifically. The image interpretation process is based on a complex interplay of psychophysiological and cognitive processes.5Bruno M.A. Walker E.A. Abujudeh H.H. Understanding and confronting our mistakes: the epidemiology of error in radiology and strategies for error reduction.Radio Graphics. 2015; 35: 1668-1676Google Scholar It is important to note that overall evidence indicates that radiologists' errors are not the result of carelessness or negligence, but rather are the result of the very complex processes involved in CXR interpretation.13Baker S.R. Patel R.H. Yang L. Lelkes V.M. Castro III, A. Malpractice suits in chest radiology: an evaluation of the histories of 8265 radiologists.J Thorac Imaging. 2013; 28: 388-391Crossref PubMed Scopus (30) Google Scholar,15Berlin L. Radiologic errors, past, present and future.Diagnosis. 2014; 1: 79-84Crossref Scopus (46) Google Scholar, 16Revesz G. Kundel H.L. Psycholphysical studies of detection errors in chest radiology.Radiology. 1977; 123: 559-562Crossref PubMed Scopus (59) Google Scholar, 17Siegle R.L. Baram E.M. Reuter S.R. et al.Rates of disagreement in imaging interpretation in a group of community hospitals.Acad Radiol. 1998; 5: 148-154Abstract Full Text PDF PubMed Scopus (76) Google Scholar, 18Kim Y.W. Mansfield L.T. Fool me twice: delayed diagnoses in radiology with emphasis on perpetuated errors.AJR Am J Roentgenol. 2014; 202: 465-470Crossref PubMed Scopus (125) Google Scholar, 19Taylor G.A. Perceptual errors in pediatric radiology.Diagnosis. 2017; 4: 141-147Crossref Scopus (9) Google Scholar Classically, three fundamental steps in the CXR interpretation process have been recognized: search and detect, recognition, and decision.20Kundel H.L. Nodine C.F. Carmody D. Visual scanning, pattern recognition and decision-making in pulmonary nodule detection.Invest Radiol. 1978; 13: 175-181Crossref PubMed Scopus (396) Google Scholar Seminal studies by Kundel et al20Kundel H.L. Nodine C.F. Carmody D. Visual scanning, pattern recognition and decision-making in pulmonary nodule detection.Invest Radiol. 1978; 13: 175-181Crossref PubMed Scopus (396) Google Scholar using eye tracking pointed to three categories of visual misses: (1) search error, in which the eyes never fixate on a lesion, and thus it is not seen; (2) error of recognition, in which the observer fixates on a lesion, but for less than the threshold time required to recognize it as an abnormality; and (3) decision error, in which fixation on a lesion is longer than the time required for recognition, but the observer fails to recognize it as an abnormality or actively disregards it. The key component of the perceptual phase of CXR interpretation is that of visual search. A systematic, comprehensive approach to reading CXR images is important to assure all portions of the CXR image are inspected and analyzed.21Delrue L. Gosselin R. Ilsen B. et al.Difficulties in the interpretation of chest radiography.in: Coche E. Ghaye B. de Mey J. Duyck P. Comparative Interpretation of CT and Standard Radiography of the Chest. Springer, 2011: 27-49Crossref Google Scholar This is particularly essential during training and for more novice readers. Studies using eye tracking have demonstrated that experienced radiologists use a more efficient, free, and global search, rather than scanning the CXR image with a preconceived orderly pattern.21Delrue L. Gosselin R. Ilsen B. et al.Difficulties in the interpretation of chest radiography.in: Coche E. Ghaye B. de Mey J. Duyck P. Comparative Interpretation of CT and Standard Radiography of the Chest. Springer, 2011: 27-49Crossref Google Scholar Evidence has shown that experienced radiologists perceive most abnormalities within the first few seconds of viewing. In fact, < 300 ms may suffice to identify major features of lesions. This rapid identification of abnormalities increases with experience.22Brogdon B.G. Kelsey C.A. Moseley Jr., R.D. Factors affecting perception of pulmonary lesions.Radiol Clin North Am. 1983; 21: 633-654Abstract Full Text PDF PubMed Google Scholar After this rapid phase is a slower, more deliberate, confirmatory and discovery phase to assure more difficult so-called blind-spot lesions are not overlooked and to take a second look in response to clinical indication. Analogous to the "thinking fast and slow" principle of Kahneman23Kahneman D. Thinking Fast and Slow. Farrar, Straus and Giroux, 2011Google Scholar is "perceiving fast and slow."24Nodine C.F. Mello-Thoms C. Kundel H.L. Weinstein S.P. Time course of perception and decision making during mammographic interpretation.AJR Am J Roentgenol. 2002; 179: 817-823Crossref Scopus (161) Google Scholar,25Kundel H.L. Nodine C.F. A visual concept shapes image perception.Radiology. 1983; 146: 363-368Crossref PubMed Scopus (103) Google Scholar Such an approach requires extensive experience and is not advisable for less experienced readers, who should maintain a consistent, systematic approach to avoid missing important findings. Among the multiple causes of perceptual errors are: (1) poor conspicuity of target lesions resulting from suboptimal technical factors, which include image acquisition, processing, and display parameters; (2) poor conspicuity of abnormalities resulting from intrinsic low contrast (eg, ground-glass lung nodules and opacities) or subtle contour alterations (eg, mediastinal or hilar lesions); (3) overlapping structures and blind spots, described herein; (4) incomplete visual search, including satisfaction of search, in which visual scanning of the image is terminated after an initial abnormality is detected; (5) inattentional blindness, a psychological phenomenon in which a seemingly obvious finding is not noticed because attention is being focused on a different search task26Drew T. Vo M.L.H. Wolfe J.M. The invisible gorilla strikes again: sustained inattentional blindness in expert observers.Phychol Sci. 2013; 24: 1848-1853Crossref PubMed Scopus (306) Google Scholar; (6) suboptimal viewing conditions, including ambient lighting, distractions, and fatigue; and (7) overly rapid image interpretation speed. Many perceptual errors remain unexplained. The principle causes of cognitive errors, in addition to lack of domain knowledge, are the consequence of cognitive biases, of which > 40 have been described.5Bruno M.A. Walker E.A. Abujudeh H.H. Understanding and confronting our mistakes: the epidemiology of error in radiology and strategies for error reduction.Radio Graphics. 2015; 35: 1668-1676Google Scholar Among the more common cognitive biases are anchoring (latching onto initial data), framing (being influenced by the way a case is presented), alliterative (being overly influenced by prior reports), and expectation bias (missing findings which are unexpected to be present or absent). In many patients, CXR provides the first opportunity to detect early lung cancer by the detection of incidental pulmonary nodules, despite the fact that screening is performed by low-dose CT scan imaging.27Tam M.D.B.S. Dyer T. Dissez G. et al.Augmenting lung cancer diagnosis on chest radiographs: positioning artificial intelligence to improve radiologist performance.Clin Radiol. 2021; 76: 607-614Abstract Full Text Full Text PDF PubMed Scopus (10) Google Scholar Unfortunately, these incidental nodules often are missed. The percentage of lung cancers missed on CXR that can be seen in retrospect ranges from 20% to 30%28American College of Radiology Data Science InstituteIncidental pulmonary nodules on chest radiograph. 2022. American College of Radiology Data Science Institute website.https://www.acrdsi.org/DSI-Services/Define-AI/Use-Cases/Incidental-Pulmonary-Nodules-on-Chest-RadiographDate accessed: January 7, 2022Google Scholar to as high as 90%.29Forrest J.V. Friedman P.J. Radiologic errors in patients with lung cancer.West J Med. 1981; 134: 485-490PubMed Google Scholar, 30Muhm J.R. Miller W.E. Fontana R.S. Sanderson D.R. Uhlenhapp M.A. Lung cancer detected during a screening program using four-month chest radiographs.Radiology. 1983; 148: 609-615Crossref PubMed Scopus (326) Google Scholar, 31Austin J.H. Romney B.M. Goldsmith L.S. Missed bronchogenic carcinoma: radiographic findings in 27 patients with a potentially respectable lesion evident in retrospect.Radiology. 1992; 182: 115-122Crossref PubMed Google Scholar Countries other than the United States seem to be showing similar statistics.32Turkington P. Misinterpretation of the chest X-ray as a factor in the delayed diagnosis of lung cancer.Postgrad Med J. 2002; 78: 158-160Crossref PubMed Scopus (55) Google Scholar In 90% of cases in which a presumed mistake in lung cancer diagnosis has occurred, the error occurred on CXR.13Baker S.R. Patel R.H. Yang L. Lelkes V.M. Castro III, A. Malpractice suits in chest radiology: an evaluation of the histories of 8265 radiologists.J Thorac Imaging. 2013; 28: 388-391Crossref PubMed Scopus (30) Google Scholar,33Del Ciello A. Franchi P. Contegiacomo A. et al.Missed lung cancer: when, where and why?.Diagn Interv Radiol. 2017; 23: 118-126Crossref PubMed Scopus (87) Google Scholar,34White C.S. Salis A.L. Meyer C.A. Missed lung cancer on chest radiography and computed tomography: imaging and medicolegal issues.J Thorac Imaging. 1999; 14: 63-68Crossref PubMed Scopus (53) Google Scholar As previously mentioned, the leading cause of these missed diagnoses is observer error. This often results from overlapping anatomic structures, including ribs and their costochondral junctions, clavicles, spine, mediastinum, heart, hila, pulmonary vessels, and diaphragms (Figure 1, Figure 2, Figure 3, Figure 4). Common blind spots where lung nodules can be missed on the posteroanterior view, as illustrated in Figure 5, include the lung apices (Fig 6), extending along the paramediastinal areas (Fig 1) and the hilar regions (Fig 7). These areas have been referred to informally as "the legal zone." Additional blind spots are the areas of the lung superimposed on the heart (Fig 2) and projected below the domes of the diaphragm (Fig 3). The lateral radiograph plays an important role in allowing further evaluation of these blind-spot regions on the posteroanterior view (Figure 2, Figure 3, Figure 4, Figure 8). However, it should be noted that relative blind spots also exist on the lateral radiograph, depicted in Figure 5. The most common of these are the posterior and apical portions of the upper lobes, overlying the spine, and over the superior heart.35Novak S. David A. Zigmund B. What's lurking in the shadows? A pictorial review of blindspots on chest radiographs and the perils of overlooking them. Poster presented at: EEE-06-18 4th World Congress of Thoracic Imaging 2017, Boston, MA2017Google Scholar Also contributing to missed lung nodules and lung cancers are tumor characteristics, including small size, low lesion attenuation (ground glass) (Fig 9), ill-defined margins,3Waite S. Scott J. Gale B. et al.Interpretive error in radiology.AJR Am J Roentgenol. 2017; 208: 1-11Crossref PubMed Scopus (125) Google Scholar,22Brogdon B.G. Kelsey C.A. Moseley Jr., R.D. Factors affecting perception of pulmonary lesions.Radiol Clin North Am. 1983; 21: 633-654Abstract Full Text PDF PubMed Google Scholar,34White C.S. Salis A.L. Meyer C.A. Missed lung cancer on chest radiography and computed tomography: imaging and medicolegal issues.J Thorac Imaging. 1999; 14: 63-68Crossref PubMed Scopus (53) Google Scholar,36Chotas H.G. Ravin C.E. Chest radiography: estimated lung volume and projected area obscured by the heart, mediastinum, and diaphragm.Radiology. 1994; 226: 221-230Google Scholar, 37Quekel L.G.B.A. Kessels A.G.H. Goei R. et al.Miss rate of lung cancer on the chest radiograph in clinical practice.Chest. 1999; 115: 720-724Abstract Full Text Full Text PDF PubMed Scopus (267) Google Scholar, 38Austin J.H.M. Romney B.M. Goldsmith L.S. Missed bronchogenic carcinoma: radiographic findings in 27 patients with a potentially resectable lesion evident in retrospect.Radiology. 1992; 182: 115-122Crossref PubMed Scopus (244) Google Scholar, 39Wu M.H. Gotway M.B. Lee T.J. et al.Features of non-small cel lung carcinomas overlooked at digital chest radiography.Clin Radiol. 2008; 63: 518-528Abstract Full Text Full Text PDF PubMed Scopus (26) Google Scholar, 40delCiello A. Franchi P. Contegiacomo A. et al.Missed lung cancer: when, where, and why?.Diagn Interv Radiol. 2017; 23: 118-126Crossref PubMed Scopus (90) Google Scholar and the presence of other lung opacities.41Samuel S. Kundel H.L. Nodine C.F. et al.Mechanism of satisfaction of search: eye position recordings in the reading of chest radiographs.Radiology. 1995; 194: 895-902Crossref PubMed Scopus (143) Google ScholarFigure 2Images from a 34-y-old woman with a small pulmonary nodule in the left lower lobe. A, On posteroanterior chest radiograph, note was made of a nodular opacity superimposed on the inferior heart just above the medial left hemidiaphragm (arrow). The nodule is located within one of the blind spots where lung nodules commonly are missed (Fig 5). B, Lateral chest radiograph showing the nodule overlying the lower thoracic spine (arrow). C, Axial noncontrast CT scan demonstrating the corresponding lobulated nodule with pleural indentation in the left lower lobe.View Large Image Figure ViewerDownload Hi-res image Download (PPT)Figure 3Images from an 82-y-old woman with right lower lobe non-small cell lung cancer. A, On posteroanterior chest radiograph, note was made of a round opacity at the right lung base, superimposed on the right hemidiaphragm (arrows). The lesion may be missed easily without attention to the blind spots in the lungs. B, Lateral chest radiograph showing the opacity overlying the mid to lower thoracic spine (arrow). C, Axial CT scan with contrast enhancement demonstrating the corresponding mass in the right lower lobe abutting the pleura. Multiple liver metastases also are seen.View Large Image Figure ViewerDownload Hi-res image Download (PPT)Figure 4Images from a 56-y-old man with right lower lobe non-small cell lung cancer. A, On posteroanterior chest radiograph, note was made of an opacity at the medial right lung base, superimposed on the right heart and the right descending pulmonary artery (arrows). B, Lateral chest radiograph more clearly visualizing this opacity anterior to the lower thoracic spine. C, Axial CT scan demonstrating the corresponding mass in the right lower lobe.View Large Image Figure ViewerDownload Hi-res image Download (PPT)Figure 5Be aware of the common locations of missed pulmonary nodules, the so-called blind spots. A, Posteroanterior chest radiograph showing that these include: (1) lung apices, in areas surrounded by the first ribs; (2) juxtamediastinal regions between the apices and hila; (3) hilar regions; (4) retrocardiac areas; and (5) lung areas projected beneath the diaphragms. B, Lateral chest radiograph showing that these include: (6) lung overlying the lateral spine, (7) posterior and apical upper lobes, and (8) lung superimposed on the superior heart. (Courtesy of Dr Mizuki Nishino at Brigham and Women's Hospital, Boston. Modified from RSNA 2004 Educational Exhibit "Hide and Seek: Subtle pulmonary nodules on chest radiograph. Mizuki Nishino, MD and Hiroto Hatabu, MD, PhD)35Novak S. David A. Zigmund B. What's lurking in the shadows? A pictorial review of blindspots on chest radiographs and the perils of overlooking them. Poster presented at: EEE-06-18 4th World Congress of Thoracic Imaging 2017, Boston, MA2017Google ScholarView Large Image Figure ViewerDownload Hi-res image Download (PPT)Figure 6Images from a 49-y-old man with a superior sulcus tumor in the right apex with destruction of the right second rib (arrow). A, posteroanterior chest radiograph showing asymmetry is a clue to identify the abnormality. B, Coronal reformatted CT scan with contrast-enhancement demonstrating the right apical mass with chest wall invasion and destruction of the rib.View Large Image Figure ViewerDownload Hi-res image Download (PPT)Figure 7Images from a 58-y-old woman with left lower lobe non-small cell lung cancer. A, On posteroanterior chest radiograph, note was made of subtle increased opacity in the left infrahilar area (arrows). B, Lateral chest radiograph showing the corresponding opacity anterior to the mid thoracic spine (arrows). C, D, Prior posteroanterior (C) and lateral (D) chest radiographs showing that the abnormality is more easily identified by comparison. E, Axial contrast-enhanced CT scan demonstrating the corresponding hilar mass with heterogenous enhancement in the left lower lobe. This case illustrates the importance of comparison with prior radiographs and that even large masses in the hilar region may be difficult to detect. Knowledge of normal hilar anatomic features is essential.View Large Image Figure ViewerDownload Hi-res image Download (PPT)Figure 8Images from a 62-y-old woman with carcinoid tumor in the right middle lobe. A, On posteroanterior chest radiograph, note was made of a subtle asymmetric opacity superimposed on the mid portion of the right descending pulmonary artery (arrow). B, Lateral chest radiograph showing the nodule to better advantage anteriorly in the right middle lobe (arrow). C, Axial noncontrast CT scan demonstrating the corresponding lobulated lesion in the right middle lobe.View Large Image Figure ViewerDownload Hi-res image Download (PPT)Figure 9Images from an 89-y-old woman with a small, low-density nodule in the right middle lobe. A, On posteroanterior chest radiograph, note was made of a faint asymmetric opacity overlying the anterior aspect of the right fifth rib (arrow). B, Axial noncontrast CT scan demonstrating the corresponding small spiculated nodule in the right middle lobe with traction of the right major fissure (arrow). Lung cancers presenting as small, low-density nodules can be missed on chest radiography.View Large Image Figure ViewerDownload Hi-res image Download (PPT) Opacities resulting from pneumonia may be subtle (Fig 10) and may occur within the blind-spot regions described herein. In particular, pneumonia frequently may be overlooked when at the lung bases and superimposed on the diaphragms. Therefore, it is important to use lateral radiography, in which pneumonias in the retrocardiac and diaphragmatic regions can be more apparent than on the posteroanterior view. Chest CT scans, including those obtained to evaluate for pulmonary embolism, not infrequently reveal a pneumonia overlooked on the CXR. The findings of pneumothorax can be subtle and missed (Fig 11) because the very thin white line of the displaced visceral pleura can be overlooked, and the air in the pneumothorax space is not readily differentiated from that of the peripheral lung. The detection of a pneumothorax can be particularly challenging in the supine position, in which the pleural air predominates at the lung bases (the most nondependent region when supine), rather than the typical apical distribution. A supine pneumothorax can be recognized by the deep sulcus sign, along with basilar hyperlucency. Flattening of the ipsilateral hemidiaphragm and contralateral displacement of the mediastinum on inspiration are indica
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