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Walif Chbeir: Medical Imaging of PneumoThorax (PNO)–3

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Dr. Walif Chbeir outlines in detail the medical imaging practice and diagnostic approach of pneumothorax (also known as PNO). This is the third in a four-part piece on PNO by Chbeir.

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Walif Chbeir: Medical Imaging of PneumoThorax (PNO)–3

  1. 1. Edited March02,2016 Update sept 30, 2016 Medical Imaging of PneumoThorax (PNO3) Dr WALIF CHBEIR C- UltraSound 1- Introduction: * Lung sonography has rapidly emerged as a reliable technique in the evaluation of various thoracic diseases. One important, well established application is the diagnosis of a pneumothorax. * Ultrasound has a higher sensitivity than the traditional upright anteroposterior chest radiography (CXR) for the detection of a pneumothorax. (Sonographic diagnosis of pneumothorax) - Small occult pneumothoraces may be missed on CXR during a busy trauma scenario, and CXR may not always be feasible in critically ill patients. - In certain studies, the sensivity of US has been similar to that found in CT scan. * Initial Ultrasonographic evaluation of the chest in the critically ill patient (Focus On: Ultrasound Detection of Traumatic Anterior Pneumothorax.) demonstrated the superiority of bedside ultrasound in the detection of anterior pneumothoraces, compared with supine chest radiographs (CXR). - Recent data from acutely injured patients support the initial studies by demonstrating that bedside ultrasound is more sensitive than chest radiography in the detection of an anterior pneumothorax when computed tomography (CT) is used as the gold standard. (Focus On: Ultrasound Detection of Traumatic Anterior Pneumothorax). * Computed tomography, the gold standard for the detection of pneumothorax, requires patients to be transported out of the clinical area, compromising their hemodynamic stability and delaying the diagnosis. * As ultrasound machines have become more portable and easier to use, lung sonography now allows a rapid evaluation of an unstable patient, at the bedside. These advantages combined
  2. 2. with the low cost and ease of use, have allowed thoracic sonography to become a useful modality in many clinical settings. * The Focused Assessment with Sonography in Trauma (FAST) examination has now been modified to include lung imaging as part of the evaluation in a trauma patient. The application has been renamed as the EFAST examination, with ‘E’ standing for extended, including the standard lung views. * The diagnosis of a pneumothorax is usually made with a combination of clinical signs and symptoms, which may be subtle, and plain chest radiography. -- Regardless of its presentation, the early detection and treatment of a pneumothorax is critical. -- Small( 10% or less) or medium (11 to 40%) sized pneumothoraces are generally not lifethreatening and their management varies. - However, a delay in the diagnosis and treatment, especially in those who are mechanically ventilated, may lead to the progression of a pneumothorax and resultant hemodynamic instability. In these critical situations where a subtle pneumothorax may be missed, a quick bedside lung ultrasound may expedite the diagnosis, treatment, and resuscitation of a patient who may have otherwise decompensated. * These findings underline the utility of performing a rapid bedside ultrasound, in emergent traumatic setting, to possibly aid in the diagnosis, prior to sending a patient for a CT scan. 2-Probe selection and equipment - The bedside sonographic diagnosis of pneumothorax can be performed with most ultrasound machines, which is especially helpful in the critically ill and hemodynamically unstable patient, as it obviates the need for transport. - A straight linear array high frequency probe (5–13 MHz) may be most helpful in analyzing superficial structures such as the pleural line and providing better resolution. - A microconvex or curvilinear array probe may be more suitable for deeper lung imaging as it provides better penetration (1–8 MHz), at the cost of less resolution. - Finally, some advocate the use of the phased array probe, generally used in cardiac imaging (2–8 MHz), as its flat and smaller footprint is better suited for imaging in between the ribs. 3- Technique and normal anatomy
  3. 3. * - A pneumothorax contains air and no fluid, and therefore, will rise to the least dependent area of the chest. In a supine patient this area corresponds to the anterior region of the chest at approximately the second to fourth intercostal spaces in the midclavicular line. So, this location will identify the majority of significant pneumothoraces in the supine patient. - In contrast, air will accumulate in an apicolateral location in an upright patient. - Based on the above, patients are scanned in a supine or near to supine position. The probe should be placed in a sagittal position (indicator pointing cephalad) on the most anterior region of the chest (usually around the nipple line/4th-5th rib space). In general, scanning of 2 - 3 intercostal spaces in the midclavicular line is recommended. See fig2, in Sonographic diagnosis of pneumothorax, in J Emerg Trauma Shock. 2012 Jan-Mar; 5(1): 76–81, in PMC free articles, PMCID: PMC3299161, Received 2011 Jun 1; Accepted 2011 Jun 6, (Page consulted February 12, 2016). All right reserved. Go to http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3299161 http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3299161/figure/F1/ - The sonographer should first identify the landmarks of two ribs with posterior shadowing behind them and visualize the pleural line in between them. This is typically called ‘the bat sign’ where the periosteum of the ribs represents the wings and the bright hyperechoic pleural line in between them represents the bats’ body. See Fig 2 in Sonographic diagnosis of pneumothorax, in J Emerg Trauma Shock. 2012 Jan-Mar; 5(1): 76–81, in PMC free articles, PMCID: PMC3299161, Received 2011 Jun 1; Accepted 2011 Jun 6, (Page consulted February 12, 2016). All right reserved. Go to http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3299161 http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3299161/figure/F2/ - If the ribs are not visualized the probe should be slowly moved in a caudal direction (inferiorly) until two ribs appear on the screen. It is in between these two rib landmarks that the two layers of pleura, parietal and visceral, are seen sliding across one another. As stated earlier,
  4. 4. air will rise to the anterior chest wall, and therefore a pneumothorax that is large enough to require a chest tube will appear with this simple technique. * The presence of pleural sliding is the most important finding in normal aerated lung. Lung sliding corresponds to the to and fro movement of the visceral pleura on the parietal pleura that occurs with respiration. It is a dynamic sign and can be identified on ultrasound as horizontal movement along the pleural line. Sliding is best seen at the lung apex in a supine patient. .The most important point to remember with lung sliding is that its signs arise at and below the pleural line and never above (vital to misinterpreting muscular sliding in dyspnoea and subcutaneous emphysema). If there is subcutaneous emphysema it can usually be moved out of the way with pressure from the probe. * The use of M mode, which detects motion over time, provides more evidence that the pleural line is sliding. It is beneficial in patients where sliding may be subtle, such as, in the elderly or in patients with poor pulmonary reserve, who are not taking large breaths. The M mode cursor is placed over the pleural line and two different patterns are displayed on the screen: The motionless portion of the chest above the pleural line creates horizontal ‘waves,’ and the sliding below the pleural line creates a granular pattern, the ‘sand’. The resultant picture is one that resembles waves crashing in onto the sand and is therefore called the ‘seashore sign’ and is present in normal lung. See Fig 3 in Sonographic diagnosis of pneumothorax, in J Emerg Trauma Shock. 2012 Jan-Mar; 5(1): 76–81, in PMC free articles, PMCID: PMC3299161, Received 2011 Jun 1; Accepted 2011 Jun 6, (Page consulted February 12, 2016). All right reserved. Go to http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3299161 http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3299161/figure/F3/ * ‘B lines’ or ‘comet tail artifacts’ are reverberation artifacts that appear as hyperechoic vertical lines that extend from the bright white hyperechoic pleural line to the edge of the screen without fading. ‘Comettail artifacts’ move synchronously with lung or pleural sliding and respiratory movements., in a normal well-aerated lung. - These artifacts are seen in normal lung due to the acoustic impedance differences between water and air.
  5. 5. - A few visualized ‘B lines’ in dependent regions are expected in normal aerated lung and are visualized moving along with the sliding pleura. - Excessive ‘B lines’, especially in the anterior lung, are abnormal and are usually indicative of interstitial edema. See Fig 4 in Sonographic diagnosis of pneumothorax, in J Emerg Trauma Shock. 2012 Jan-Mar; 5(1): 76–81, in PMC free articles, PMCID: PMC3299161, Received 2011 Jun 1; Accepted 2011 Jun 6, (Page consulted February 12, 2016). All right reserved. Go to http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3299161 http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3299161/figure/F4/ * The average time to perform this examination varies from two to three minutes; less than one minute to rule out a pneumothorax and several minutes to rule it in. 4-Sonographic signs of pneumothorax 1-Absence of lung sliding: * In a pneumothorax, there is air present that separates the visceral and parietal pleura and prevents visualization of the visceral pleura. In this situation, lung sliding is absent. This lack of lung sliding can be visualized by identifying the landmarks discussed earlier. Two ribs should be identified with the pleural line in between them. The typical to and fro movement or shimmering of the pleural line will not be present. * The same technique using M mode can be used to confirm a lack of sliding. The resultant M mode tracing in a pneumothorax will only display one pattern of parallel horizontal lines above and below the pleural line, exemplifying the lack of movement. This pattern resembles a ‘barcode’ and is often called the ‘stratosphere sign’. See Fig 5 in Sonographic diagnosis of pneumothorax, in J Emerg Trauma Shock. 2012 Jan-Mar; 5(1): 76–81, in PMC free articles, PMCID: PMC3299161, Received 2011 Jun 1; Accepted 2011 Jun 6, (Page consulted February 12, 2016). All right reserved. Go to http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3299161 http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3299161/figure/F5/
  6. 6. * The negative predictive value for lung sliding is reported as 99.2–100%, indicating that the presence of sliding effectively rules out a pneumothorax. - However, the absence of lung sliding does not necessarily indicate that a pneumothorax is present. Lung sliding is abolished in a variety of conditions other than pneumothorax, including acute respiratory distress syndrome (ARDS), pulmonary fibrosis, large consolidations, pleural adhesions, atelectasis, right mainstem intubation, and phrenic nerve paralysis. * Specificity values range from 60–99% depending on the patient population, with higher values in the general population and lower values in the Intensive Care Unit and in those with ARDS. - Although the absence of lung sliding is not specific for pneumothorax, the combination of this with other signs improves the accuracy of the diagnosis. 2- loss of Comet tail artifacts or ‘B lines’ * Ultrasound demonstrates the loss of ‘comettail artifacts’ in patients with a pneumothorax. These reverberation artifacts are lost due to air accumulating within the pleural space. * The negative predictive value for this artifact is high, reported at 98–100%, such that visualization of even one comettail essentially rules out the diagnosis of a pneumothorax. 3- A lines are other important thoracic artifacts that can help in the diagnosis of a pneumothorax. - These are also reverberation artifacts appearing as equally spaced repetitive horizontal hyperechoic lines reflecting off of the pleura. The space in between each A line corresponds to the same distance between the skin surface and the parietal pleura. See Fig 5 in Sonographic diagnosis of pneumothorax, in J Emerg Trauma Shock. 2012 Jan-Mar; 5(1): 76–81, in PMC free articles, PMCID: PMC3299161, Received 2011 Jun 1; Accepted 2011 Jun 6, (Page consulted February 12, 2016). All right reserved. Go to http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3299161 http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3299161/figure/F5/
  7. 7. - In the normal patient, when ‘B lines’ are present, they extend from the pleural line and erase ‘A lines’, as they emanate out to the edge of the screen. - ‘A lines’ will be present in a patient with a pneumothorax, but ‘B lines’ will not. - If lung sliding is absent with the presence of ‘A lines’, the sensitivity and specificity for an occult pneumothorax is as high as 95 and 94%, respectively. 4- Lung- point sign * The ‘lung- point sign’ occurs at the border of a pneumothorax. It is due to sliding lung intermittently coming into contact with the chest wall during inspiration and is helpful in determining the actual size of the pneumothorax. * This sign can further be delineated using M mode where alternating ‘seashore’ and ‘stratosphere’ patterns are depicted over time. See Fig 7 in Sonographic diagnosis of pneumothorax, in J Emerg Trauma Shock. 2012 Jan-Mar; 5(1): 76–81, in PMC free articles, PMCID: PMC3299161, Received 2011 Jun 1; Accepted 2011 Jun 6, (Page consulted February 12, 2016). All right reserved. Go to http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3299161 http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3299161/figure/F7/ * The ‘lung point sign’ is 100% specific for pneumothorax and defines its border. The location of the lung point is beneficial in determining the size of the pneumothorax. * If a lack of lung sliding is visualized anteriorly, the probe can progressively be moved to more lateral and posterior positions on the chest wall searching for the location of the lung-point. The more lateral or posterior the ‘lung-point sign’ is identified, the larger the pneumothorax. * Therefore, if the ‘lungpoint sign’ is seen in an anterior location on the chest wall, the sonographer can be assured that the pneumothorax is relatively small. Although the specificity is high, the sensitivity of the ‘lung-point sign’ is relatively low (reported at 66%) and is not seen in cases of total lung collapse. * Studies have shown concordance between pneumothorax size on ultrasound and CT scan, reportedly within 1.9–2.3 cm (ref. 28 in Sonographic diagnostic of PNO).
  8. 8. * The determination of the size of a pneumothorax is important for clinical decision making, as larger pneumothoraces are more likely to require thoracostomy. 5-Other signs * The ‘Power Slide’ refers to the use of power (angiography) Doppler to help identify lung sliding. - Power Doppler is very sensitive and picks up subtle flow and movement. - If there is lung sliding present, power Doppler will light up the sliding pleural line with color flow. See Fig 8 in Sonographic diagnosis of pneumothorax, in J Emerg Trauma Shock. 2012 Jan-Mar; 5(1): 76–81, in PMC free articles, PMCID: PMC3299161, Received 2011 Jun 1; Accepted 2011 Jun 6, (Page consulted February 12, 2016). All right reserved. Go to http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3299161 http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3299161/figure/F8/ - This technique can be helpful in cases of subtle sliding when direct visualization may be difficult. - The disadvantage of this type of Doppler is that due to its increased sensitivity, the probe needs to be held in a steady manner and the patient has to be motionless in order to prevent artifact and erroneous color flow over the pleural line, when sliding is actually absent. * The ‘lung pulse’ refers to the rhythmic movement of the pleura in synchrony with the cardiac rhythm. It is best viewed in areas of the lung adjacent to the heart, at the pleural line. These movements form a T (T Line) with the pleural line on Mmode. - The ‘lung pulse’ is a result of cardiac vibrations being transmitted to the lung pleura in poorly aerated lung. Cardiac activity is essentially detected at the pleural line when there is absent lung sliding. - In normal well aerated lung, the ‘lung pulse’ is not present. - As transmission through lung is required they rule out a pneumothorax.
  9. 9. 5- Limitations * Lack of lung sliding and comet tail artifacts may not always indicate a pneumothorax. Recently intubated patients may have a mainstem bronchus intubation preventing adequate aeration of one lung and not demonstrate either lung sliding or comet tail artifacts, giving the operator a false impression of pneumothorax. * Causes of Reduced sliding - Low tidal volume (ventilator settings, abdominal compartment syndrome, acute asthma etc) -ARDS. * Causes of Abolished sliding: Pneumothorax / Severe consolidation / ARDS / Atelectasis/ Pneumonectomy. Pneumonia and ARDS abolish sliding by adherences secondary to inflammation (exudative process) otherwise known as pleural symphysis. Both will usually show B lines allowing the ruling out of pneumothorax. * Bullae: Even with large bullae the 2 pleural layers are still opposed so sliding will still be observed. Therefore bullae should not causes false positives for pneumothorax. * If a pneumothorax is septated there may be some septa still attached to the parietal pleura giving rise to B lines at these points. This is more likely to be observed in cases of recurrent pneumathoraces. There will be no sliding and the lung point will still be visible. * Occasionally pneumothoraces may not be anterior for example where there are lung contusions stopping the free movement of air against gravity. This is more commonly seen in children. They will be visible in the axillae. * Also, when evaluating the paracardiac regions on the left chest, care must be taken to identify the pleural line. The heart rises and falls with the movement of the diaphragm, and this motion may be misinterpreted as a "lung point," especially if the probe marker is pointed caudad instead of cephalad (as recommended). 6- Management * A small anterior pneumothorax will usually not need draining even in mechanical ventilation. They can resolve spontaneously.
  10. 10. - It should be regularly assessed however as it can evolve. Check the lung point is not moving laterally. Lung protective ventilation will lessen the chances of a pneumothorax increasing in size. A lateral lung point suggests a drain will be required. - Repeat CXRs are not required. US is better for monitoring a pneumothorax. * US should be routine after procedures which may cause a pneumothorax (central line insertion, thoracocentesis). * Mapping the location of a pneumothorax means that traditional insertion sites for drains do not need to be used. Drains should be inserted away from the lung point. * US should be used to demonstrate that the lung had expanded following drainage. It can then also be used to show that the lung remains expanded (the leak has sealed) following clamping a drain thus allowing confident removal before again repeating US to confirm no reaccumulation of air post removal. * In stable trauma patients with ultrasonographic signs of a pneumothorax and a negative supine chest radiograph, we recommend a repeat upright plain film after clearance of cervical immobilization for confirmation of an occult pneumothorax. - In patients where cervical immobilization cannot be removed, we recommend computed tomography of the chest to delineate the pneumothorax early in trauma care (before transportation or intubation). * Lung-ultrasonography can prove an alternative diagnostic procedure in the difficult diagnosis of pneumothorax in critically ill patients with severe ARDS, which not only permits bedside assessment of lung pathology but also assists in the evaluation of mechanical ventilation parameters, as well as the evaluation of lung overdistension and PEEP-induced lung recruitment (ARDS et PNO; Journal of Thoracic Disease). * Recently, US has been used to assist in the placement of chest tubes, and in aspiration of loculated pneumothorax. (Ultrasound-assisted aspiration of loculated pneumothorax: A new technique) . 7- CONCLUSIONS * Thoracic sonography for the detection of pneumothorax has become a well established modality in the acute care setting. It is indispensible in the blunt or penetrating chest trauma patient, where the identification of a pneumothorax can prevent lifethreatening consequences.
  11. 11. * The traditional upright AP radiograph has become less important due to its poor sensitivity in diagnosing a pneumothorax compared to ultrasound. * Although CT scan remains the gold standard and may still catch smaller occult pneumothoraces that ultrasound misses, its disadvantages are becoming more apparent. * Bedside ultrasound obviates the need for patient transport in unstable situations, it eliminates radiation exposure, it is quicker to perform and is immediately interpreted at the bedside without unnecessary delays. In addition, it is more costeffective and can be repeated multiple times during a resuscitation. - In addition, ultrasound is the perfect modality in the emergency and critical care setting after performing certain procedures, such as a thoracentesis or the placement of a central line, to quickly confirm the presence of lung sliding and to rule out an iatrogenic pneumothorax. - It has also been found to be beneficial in the postintubation scenario, where a confirmation of bilateral lung sliding rules out a right mainstem intubation. - The increasing portability of newer ultrasound machines makes them easier to use in first responder and disaster settings, wilderness medicine, air medical transport, rural medicine, and even space explorations. - Studies indicate that the recognition of key artifacts in thoracic ultrasound is readily teachable to both physicians as well as nonphysician health care providers and its uses continue to expand in the out of hospital setting. 8- Vidéos 1- lung-point-sign-of-pneumothorax-on-ultrasound.mp4 Case courtesy of Dr Andrew Dixon, <a href="https://radiopaedia.org/">Radiopaedia.org</a>. From the case <a href="https://radiopaedia.org/cases/45149">rID: 45149</a> Or go to https://radiopaedia.org/articles/pneumothorax-ultrasound 2-Ultrasound Lung Scanning Tutorial with Dr. Shane Arishenkoff - Clarius https://www.youtube.com/watch?v=jh7EP7jiW98
  12. 12. 3- URL Link: https://www.youtube.com/results?search_query=pneumothorax+ultrasound

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