Hrev_master [page 6] [Emergency Care Journal 2013; 9:e3] Lung ultrasound: a valid help in the differential diagnosis between pneumothorax and pulmonary blebs Francesca Sandionigi, Francesca Cortellaro, Elisa Forni, Daniele Coen Emergency Department, Niguarda Ca’ Granda Hospital, Milano, Italy Abstract Spontaneous pneumothorax is a relatively common disease but its radiological diagnosis can be difficult because of the insufficient sen- sitivity of chest X-rays. This is even more so when bullous emphysema and acute pneu- mothorax co-exist. There is evidence that lung ultrasound is a valid instrument to detect a pneumothorax and a valid help in the differen- tial diagnosis between pneumothorax and pul- monary blebs. We present a case which sug- gests the potential superiority of lung ultra- sound on chest radiography in distinguishing free air (pneumothorax) from apical blebs, particularly when these are located in the pos- terior regions and may be easily confused with pneumothorax. Introduction Spontaneous pneumothorax (defined as the spontaneously occurring presence of air in the pleural space in patients without apparent underlying lung disease) is a relatively com- mon disease primarily affecting young and otherwise healthy individuals. Pneumothorax typically occurs in tall, thin, male gender sub- jects; smoking is a risk factor. The sponta- neous rupture of a subpleural bleb or of a bulla (usually at the lung apex) creates a communi- cation between the alveolar spaces and the pleura. An apical subpleural bleb is the most com- mon cause of a primary spontaneous pneu- mothorax, while chronic obstructive pul- monary disease is responsible for most sec- ondary spontaneous cases. The presenting symptoms are sudden onset of dyspnea, pleuritic chest pain, cough and anxiety. Physical examination can be normal when the pneumothorax is small. Rapidly evolving hypotension, tachypnea, tachycardia, and cyanosis should raise the suspicion of a tension pneumothorax, which is extremely rare among primary forms.1 Chest X-rays studies classically show a white line (pleura) outlining a distinct area of black pleural space where lung markings are absent. It can be difficult to differentiate bul- lous emphysema from acute pneumothorax by chest X-rays, especially when both entities co- exist; further, the sensitivity of X-rays is partic- ularly low when the amount of air in the pleu- ral space is limited. Computed tomography (CT) is the most sensitive and specific modal- ity for the detection of a pneumothorax and remains the reference standard. However, the use of this diagnostic technique has draw- backs in terms of costs, high dose of radiation, transport of patients and loss of time. Lung ultrasound is a valid alternative, as several studies demonstrate its accuracy in diagnos- ing a pneumothorax and defining its exten- sion.2 We present a case where bedside ultra- sound in the emergency department was cru- cial in the differential diagnosis between bul- lous disease and pneumothorax. Case Report A 21-year-old man was admitted to the emer- gency department of Niguarda Ca’ Granda Hospital in Milan presenting a three-day-histo- ry of chest pain exacerbated by respiratory acts and associated with shortness of breath. He denied sputum production, cough and fever. A left pneumothorax had been treated surgically 3 months earlier. Vital signs were in normal range as was pulse oxymetry; he had a shallow respiration with breath sounds clear and bilateral; cardiac and abdominal examinations were normal. He seemed very worried about a possible recur- rence of pneumothorax, though the symptoms observed were mild. Electrocardiogram (ECG) provided evidence of sinus tachycardia (110 bpm) and no signs of acute ischemia or peri- carditis. Chest X-ray showed a small area of hyperinflation with decreased lung markings at the right upper lobe, which was interpreted by the radiologist as a pneumothorax (Figure 1). Bedside ultrasound examination showed a normal sliding sign bilaterally excluding the presence of a pneumothorax (Figure 2). A chest CT performed 3 months earlier at anoth- er hospital helped with the diagnosis, showing a right posterior apical bleb that satisfactorily explained the current radiological images (Figure 3). Differential diagnosis of chest pain includes: myocardial ischemia, pericarditis, pleuritis, aortic dissection, pulmonary embolism, herpes zoster. All these diagnoses appeared less likely than pneumothorax or musculoskeletal pain, his young age, the char- acteristics of the pain (exacerbated by breath- ing), clinical examination, absence of risk fac- tors and normal ECG and laboratory consid- ered. The patient was then discharged with a diagnosis of non-specific thoracic pain and was prescribed analgesics. Called back in 7 days he reported well-being with complete res- olution of symptoms. Discussion Blebs or cysts can be easily mistaken for a pneumothorax. The criteria for radiographic diagnosis of pneumothorax include: i) visuali- zation of the visceral pleura separated from the chest wall with loss of lung markings laterally; ii) demonstration of a deep sulcus sign; iii) crisp definition of the hemidiaphragm; and iv) demonstration of a continuous diaphragm sign.3 When chest radiography cannot clearly provide the answer, a CT scan is recommend- ed. The use of ultrasounds to diagnose pneu- mothorax was first described in a veterinary medical journal in 1986. The following year, Wernecke et al. described sonographic recog- nition of pneumothoraces in human subjects on the basis of absence of pleural sliding and comet tail artifacts. Since then, multiple case reports and several studies have explored the use of ultrasound in the diagnosis of pneu- mothorax.4 Ultrasonographic examination of the lung and pleura can be perfomed using linear and convex probes of 3.5-7.5 MHz using intercostal spaces as an acoustic window. Patients are best examined supine, as the free thoracic air associated with a pneumotho- rax will rise to the anterior chest wall at the location where the exam is performed. Bilateral pleural interfaces are examined at the second to fourth intercostal spaces anteri- orly in the parasternal line and up to the midaxillary line to look for the lung point.3 In the supine patient, the sonographic technique Emergency Care Journal; volume 9:e3 Correspondence: Daniele Coen, Emergency Department, Niguarda Ca’ Granda Hospital, Piazza Ospedale Maggiore 3, 20162 Milano, Italy. Tel. +39.02.64447433 - Fax: +39.02.64442825. E-mail: daniele.coen@ospedaleniguarda.it Key words: lung ultrasound, pneumothorax, pul- monary bleb. Received for publication: 15 February 2013. Revision received: 5 May 2013. Accepted for publication: 6 May 2013. This work is licensed under a Creative Commons Attribution 3.0 License (by-nc 3.0). ©Copyright F. Sandionigi et al., 2013 Licensee PAGEPress, Italy Emergency Care Journal 2013; 9:e3 doi:10.4081/ecj.2013.e3 No n c om me rci al us e o nly [Emergency Care Journal 2013; 9:e3] [page 7] consists of exploring the least gravitationally dependent areas progressing more laterally.5 The study is performed at bedside, without the need to transport the patient and may be repeated as often as clinically indicated. The primary goal is to visualize normal slid- ing of the lung at the pleural line. Pleural slid- ing is the to-and-fro movement of the visceral pleura against the parietal pleura during respi- ration; the presence of air in the pleural cavity acts as a scatter of sound that prevents sono- graphic visualization of visceral pleural move- ments, so the presence of pleural sliding excludes the diagnosis of pneumothorax. The abolition of sliding alone had a sensitivity of 100% and specificity of 78% for the diagnosis of occult pneumothorax;6 a study of Dulchavsky et al. reports a true negative rate of 100% for ruling out a pneumothorax when the sliding lung sign has been shown.7 The sliding sign may be shown in the motion (M)-mode: this image is called the seashore sign and is characterized by horizon- tal lines (waves) representing the static chest wall, and a scattered region (sand), formed by the dynamic artifacts beyond the pleural line during its normal movement (Figure 2), which would be absent in the presence of a pneu- mothorax.8 Lung pulse is sliding due to the transmis- sion of heart beat movements to the pleural line: its presence, for the reasons above, excludes a pneumothorax. B-lines are vertical hyperechoic artifacts that arise from the pleural line and extend to the lower edge of the image, moving with res- piration, and erase the physiologic horizontal A-line artifacts seen in normal lungs. The pres- ence of even a single B-line indicates the absence of pneumothorax with a negative pre- dictive value of 100%.9 In case of absence of lung sliding, pulse and B lines, the lung point sign should be detected. This is the visualization of lung sliding and absent lung sliding in the same intercostal space, representing the movement of the lung at the border of the pneumothorax; it is useful both to confirm the presence of a pneumotho- rax (specificity 100%) and to delineate the lat- eral margin of the air collection and thus its extension.10 The use of ultrasounds has contributed to a better recognition of occult pneumothorax with greater sensitivity and negative predic- tive value than chest radiography and with a similar specificity. Supine anteroposterior (AP) chest radiography has been reported to have very poor sensitivity in the detection of pneumothorax (36-75%), while the sensitivity of lung ultrasound is higher (92-98%) with similar specificity (both of 99-100%); the accu- racy of chest radiography and ultrasound is respectively 74 and 96%.2,3,6,7,11,12 In addition, lung ultrasound allows the detection of a pneumothorax within 2 to 4 min compared to the 20 to 30 min necessary for chest radiography.13 Thoracic ultrasonography has also been shown to be accurate in identifying the size and extension of a pneumothorax.2,14 This case reinforces the potential superiori- ty of ultrasounds on chest radiography to dis- tinguish between free air (pneumothorax) and apical blebs, particularly when located in the posterior regions where they determine the composition of a radiological image which may be easily confused with a pneumothorax. Echography is an operator-dependent tech- nique, but its acquisition needs only a short period of training15,16 and findings of pleural disease are relatively simple to detect. Lung echography has intrinsic limitations since it offers poor visualization of the medi- astinum and is impaired by subcutaneous emphysema, obesity, pleural adhesions or any condition in which the pleural surfaces do not slide against each other with respiration. When a big bleb is located against the parietal pleura, sliding may be minimal because there may be little or no movement of the visceral pleura that covers the bleb, so that the M-mode pattern may resemble a pneumothorax.17 However, since there is no free air in the pleu- ral space, comet tailing and the pulse sign are likely to be present.18 Conclusions This case shows that lung ultrasound could be used in clinical settings when pneumotho- rax is in the differential diagnosis with pleural blebs, distinguishing free air in the pleural cavity (no B lines, absence of sliding, and pres- ence of lung point). In case of large apical blebs, lung sliding could be absent: the presence of B lines and the absence of lung point support the diagno- sis of blebs vs pneumothorax. This is just one more reason to implement this technique in emergency departments. We believe that thoracic ultrasound should become a widespread tool for emergency physicians in the near future. References 1. 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