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Walif Chbeir: Medical Imaging of PneumoThorax (PNO)–2

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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 second in a four-part piece on PNO by Chbeir.

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Walif Chbeir: Medical Imaging of PneumoThorax (PNO)–2

  1. 1. Edited March02,2016 Update on Sept 30, 2016 Medical Imaging of PneumoThorax (PNO2) Dr WALIF CHBEIR IV- Imaging A- Chest radiography * Chest radiography is the first investigation performed to assess pneumothorax, because it is simple, inexpensive, rapid, and noninvasive. Traditionally a plain radiograph of the chest, ideally with the Xray beams being projected from the back (posteroanterior, or "PA"), has been the most appropriate first investigation. These are usually performed during maximal inspiration (holding one's breath). As little as 50 mL of pleural gas may be visible on a chest radiograph, however, it is much less sensitive than chest computed tomography (CT) scanning in detecting blebs or bullae or a small pneumothorax. * As with pleural effusion, the radiographic appearance of pneumothorax depends on the radiographic projection, the patient's position, and the presence or absence of pleural adhesion and subsequent loculation. * The radiographic diagnosis of pneumothorax is usually straightforward the outer margin of the visceral pleura ( and lung), known as the pleural line, is separated from the parietal pleura (and chest wall) by a lucent gas space devoid of pulmonary vessels. -- The pleural line may be difficult to detect with a small pneumothorax unless high quality posteroanterior and lateral chest films are obtained and viewed under a bright light or under windowing and magnification on workstation -- In the upright patient, air rises in the pleural space, mostly in an apicolateral location and separates the lung from the chest wall, allowing the visceral pleural line to become visible as a
  2. 2. thin curvilinear opacity between vessel-containing lung and the avascular pneumothorax space. The (visceral) pleural line appears either straight or convex towards the chest wall and remains fairly parallel to the chest wall. - May be laterally located with apical pleural adhesions -- Supine position ( Critically ill patient, in ICU, polytraumatism). Supine radiographs are the least sensitive in detecting pneumothorax, requiring 500 mL of pleural gas—10 times more than necessary to detect air in the apicolateral pleural space on an upright chest radiograph. - If the pneumothorax is small or moderate in size ( in the setting of bronchopulmonary placement of a feeding tube on an abdominal radiograph, p.e.), the lung is not separated from the chest wall laterally or at the apex and therefore the pneumothorax may not be appreciated. - The juxtacardiac area (or anteromedial pleural recess) , cardiophrenic recess, the lateral chest wall, the subpulmonic space, the posteromedial pleural recess and the costophrenic pleural recesses are the best areas to search for evidence of pneumothorax. +++ . Actually, the highest part of the chest cavity lies anteriorly or anteromedially at the base near the diaphragm, and free pleural air rises to this region - The anteromedial pleural recess is the least dependent space in the thoracic cavity in a supine patient. A pneumothorax in this location results in a paramediastinal radiolucent band parallel to the cardiac outline, with sharp definition of the cardiac outline, known as the crisp (net) cardiac silhouette sign. An anteromedial pneumothorax may also displace the anterior junction line laterally. This can be differentiated from pneumomediastinum by determining the extent of the air collection. In pneumomediastinum, air spreads bilaterally, outlining the mediastinal structures. - Subpulmonic pneumothorax results in hyperlucency of the upper abdominal quadrant, a deep lateral costophrenic sulcus (the well-known deep sulcus sign), visualization of the anterior costophrenic sulcus, and sharp delineation of the diaphragm in the presence of an opacified lung. However, hyperlucency of an upper abdominal quadrant may also be seen in the setting of pneumoperitoneum or subphrenic abscess. - In summary, the signs of pneumothorax in a supine patient (27- Tocino IM, Miller MH, Fairfax WR. Distribution of pneumothorax in the supine and semirecumbent critically ill adult. AJR Am J Roentgenol. 1985;144:901 à 905.) 1- Relative increased lucency of the involved hemithorax 2- Increased sharpness of the adjacent mediastinal margin and diaphragm 3- Deep sulcus sign (Subpulmonic PNO): Deep, sometimes tongue-like, costophrenic sulcus; may be the only sign of PNO. 4-Visualization of the anterior costophrenic sulcus
  3. 3. 5- Increased sharpness of the cardiac borders 6- Visualization of the inferior edge of the collapsed lung above the diaphragm 7- Depression of the ipsilateral hemidiaphragm. * for equivocal cases: -- Lateral or decubitus views are recommended - On standard lateral views a visceral pleural line may be seen in the retrosternal position or overlying the vertebrae, parallel to the chest wall. - Shoot-through lateral or decubitus views may be used in ventilated patients or neonates. -- Although the value of expiratory views is controversial and seem to not increase sensitivity for PNO detection, many clinicians still find them useful in the detection of small pneumothoraxes when clinical suspicion is high and an inspiratory radiograph appears normal. -- Decubitus radiography can be helpful in differentiating PNO from apical bullous disease * Accentuation of the PNO may be obtained with lateral decubitus studies of the appropriate side (for a possible left pneumothorax, a right lateral decubitus film of the chest should be obtained, with the beam centered over the left lung). * MIMICS +++ 1- Differentiating the pleural line of a pneumothorax from that of a skin fold, clothing, vascular lines, tubing, bedding, hair, the walls of bullae and cavities or chest wall artifact is important. Artifactual densities usually do not parallel the course of the chest wall over their entire length. - Skin folds are straight or only minimally curved, and do not run parallel to the chest wall as with a true visceral pleural line. Careful inspection of the film may reveal that the artifact extends beyond the thorax or that lung markings are visible beyond the apparent pleural line ( or the artefact). In the absence of underlying lung disease, the pleural line of a pneumothorax usually parallels the shape of the chest wall. - Clothing or bed sheets may produce a similar artefact. Skin folds also form a dense line— sharp on one side and blurred on the other—in contrast to the less dense visceral pleural line.
  4. 4. The latter distinction can, however, be rather subjective. Occasionally, doubt persists. In this situation, repeat radiography after removal of clothing and repositioning of the arm will be conclusive. - Radio-opaque lines are often seen accompanying the inferior margins of ribs, which may simulate a visceral pleural line. These are often called subcostal groove. This normal variant is characterised by its faithful relation to the inferior margin of the accompanying rib, whereas visceral pleural lines diverge from the rib to parallel the chest wall. Although usually close to the adjacent rib, companion shadows may sometimes protrude inferiorly for a variable distance, giving a confusing appearance. 2- Avascular bullae or thinwalled cysts or cavities may be mistaken for a loculated pneumothorax (pneumothorax with a pleural adhesion). . A chest drain inserted into a bullous in the mistaken belief that it is a pneumothorax is not uncommon. This is not surprising as emphysema is a known predisposing factor for a pneumothorax and patients with an exacerbation of their emphysema can present with a fairly sudden worsening of their breathlessness. The pleural line caused by a pneumothorax usually is bowed at the center toward the lateral chest wall. Unlike pneumothorax, the inner margins of bullae or cysts usually are concave to the chest wall rather than convex and do not conform exactly to the contours of the costophrenic sulcus. Presence of multiple bullae elsewhere in the lung is also cue clue to the diagnosis. Decubitus radiography can be helpful in differentiating PNO from apical bullous disease. If in doubt about the diagnosis of a pneumothorax treat the patient and not the radiograph, and do not act on the appearances of a radiograph if it does not fit the clinical picture. 3- The medial border of the scapula can imitate a lung edge but once considered can be traced in continuity with the rest of the bone, revealing its true nature. 4- After pleurectomy for recurrent pneumothorax a radioopaque line may be visible at the operative site due to suture material or staples ( Radiological Review of PNO fig 8). This may be misinterpreted as a new air leak, especially if compared with preoperative radiographs or in ignorance of the history of previous surgery. This patient underwent pleurectomy for recurrent pneumothorax. Suture material at right apex (arrow) is thicker than visceral pleural line and should not be confused with recurrent air leak. Compare with adjacent apical pneumothorax (arrowhead). 5- After removal of chest drain, a straight radio-opaque line is occasionally seen here along the line of the removed tube, known as a “drain track”. This may be misinterpreted as a recurrent
  5. 5. air leak, but its straight course and precise relation to the drain position on the radiograph before removal are usually conclusive. Presumably this finding is due to indentation of the pleura by the drain. * The British Thoracic Society guidelines divide pneumothoraxes into small and large based on the distance from visceral pleural surface (lung edge) to chest wall, with less than 2 cm being small and more than 2 cm large (means that the pneumothorax occupies about 50% of the hemithorax ) +++. These guidelines have traditionally stated that the measurement should be performed at the level of the hilum with 2 cm as the cutoff, while American guidelines state that the measurement should be done at the apex of the lung with 3 cm differentiating between a "small" and a "large" pneumothorax. The latter method may overestimate the size of a pneumothorax if it is located mainly at the apex, which is a common occurrence. - A large pneumothorax is an objective indication for drainage.+++ - Clinical Calculator: Pneumothorax Degree of Collapse PercentPneumo = 100 * (1 - (LungDiameter3 / HemithoraxDiameter3 )) The size of a pneumothorax can be defined as the percentage of the hemithorax that is vacant. This percentage is estimated by taking 1 minus the ratio of the cubes of the width of the lung and hemithorax. For example, if the width of the hemithorax is 10 cm and the width of the lung is 5 cm, the ratio is 5 3 /10 3 = 0.125. Thus, the size of the pneumothorax is about 1 minus 0.125, or 87.5%. If adhesions are present between the lung and the chest wall, the lung does not collapse symmetrically, the pneumothorax may appear atypical or loculated, and the calculation is not accurate. http://www.merckmanuals.com/professional/pulmonary-disorders/mediastinal-and-pleural-disorders/pneumothorax * A large tension pneumothorax can be a life-threatening situation requiring rapid decompression. It can result from penetrating injuries or can arise spontaneously. They are serious because air exchange is compromised in both the lung with the pneumothorax and the opposite lung which is being compressed. - Radiologic signs of tension pneumothorax include controlateral displacement of Heart and mediastinal structures, inferior displacement or depression of the diaphragm, hyperlucent hemithorax, rib cage expansion and ipsilateral collapse of the lung. - Any significant degree of displacement of the mediastinum from the midline position on maximum inspiration, as well as any depression of the diaphragm, should be taken as evidence of tension , although a definite diagnosis of tension pneumothorax is difficult to make on the basis of radiographic findings.
  6. 6. . It is not unusual for the mediastinum to be shifted away from the affected lung due to the pressure differences. This is not equivalent to a tension pneumothorax, which is determined mainly by the constellation of symptoms, hypoxia, and shock. - The degree of lung collapse is an unreliable sign of tension, since underlying lung disease may prevent collapse even in the presence of tension. * Pleural effusions occur coincident with pneumothorax in 15–25% of patients, but they usually are quite small. * Hemopneumothorax occurs in 2–3% of patients with spontaneous pneumothorax. Bleeding is believed to represent rupture or tearing of vascular adhesions between the visceral and parietal pleura as the lung collapses. * The chest radiograph should also be carefully examined for evidence of underlying parenchymal lung disease . The most common of these predisposing to pneumothorax are emphysema, pulmonary fibrosis of any cause, cystic fibrosis, aggressive or cavitating pneumonia, and cystic interstitial lung diseases such as Langerhans’ cell histiocytosis and lymphangiomyomatosis. -- Detection of an underlying condition is important for several reasons. - Firstly, therapy of the parenchymal lung disease may be possible. - Secondly, unlike primary spontaneous pneumothorax, patients with secondary air leaks are not candidates for early discharge and require inpatient observation. - Finally, all but the smallest (defined as apical or less than 1 cm in depth) secondary pneumothoraxes require treatment, even when symptoms are minimal. - Apical subpleural bullae is seen up to 15% in presence of PTX. B- CT * Is the gold standard in diagnostic of PNO. * CT has increased sensitivity for pneumothorax but is not necessary for the diagnosis of pneumothorax * However, it can be useful in particular situations, for problem solving; particularly in severe emphysema.
  7. 7. - It may be necessary to diagnose pneumothorax in critically ill patients, in trauma, in whom upright or decubitus films are not possible. The main indication for computed tomography in this clinical setting is to distinguish an emphysematous bulla from a pneumothorax, which can be difficult on standard radiographs. - Emphysematous bullae may also mimic a loculated pneumothorax, particularly when there is a background of chronic lung disease. Sometimes internal lung markings are visible in a bulla using a bright light. If there is clinical doubt in a patient with symptoms then computed tomography is helpful. * High resolution computed tomography may also be helpful for Evaluation of underlying lung parenchyma when underlying parenchymal lung disease is suspected but not clearly identified or characterised by a chest radiograph. - In presumed Spontaneous primary pneumothorax, it may help to identify Frequent paraseptal &/or centrilobular emphysema. Pleural blebs are indistinguishable from subpleural bullae. CT demonstrates focal areas of emphysema in more than 80% of patients with spontaneous pneumothorax, even in lifelong nonsmokers ((Mitlehner & al in Medscape) . These areas are situated predominantly in the peripheral regions of the apex of the upper lobes. In most patients with primary spontaneous pneumothorax (Mitlehner & al in Medscape), the abnormal findings consisted of a few localized areas of emphysema (n < 5) measuring less than 2 cm in diameter. - and in secondary pneumothorax it can help to identify most of the causes listed above. - Contralateral disease commonly identified : Important for operative planning * CT scanning may prove helpful in predicting the rate of recurrence in patients with spontaneous pneumothorax. It was found (Mitlehner & al reported by Fahad M AlHameed ; Medscape) that patients with larger or more numerous blebs, as demonstrated on thoracic CT, are more likely to experience recurrences. * In critical care and in patients with severe ARDS (ARDS & PNO) , CT Scan identifie additional loculated air collections not seen with traditional radiography (Boland and associates) ( Bolland et & in Loculated Pneumothorax: A Special Challenge In Critical Care) . CT scan in patients with ARDS (ARDS and PNO)
  8. 8. . can reveal a variety of abnormalities, such as ground-glass opacification, consolidation, interstitial thickening, evidence of fibrosis and pulmonary cysts. • Chest CT is helpful in understanding the extent of the underlying lung parenchyma distraction and is quite more sensitive in identifying pneumomediastinum and pneumothorax, which are frequently observed in patients with ARDS . • In a study of 74 ARDS patients who underwent a chest-CT, 32% of all patients presented a loculated pneumothorax (mostly anteromedial) and 30% had pulmonary air cysts (always multiple and mostly bilateral) (Tagliabue M,et & in Eirini Terzi1 et&) * Cross sectional imaging guidance is occasionally necessary for drainage of loculated pneumothoraxes in difficult locations. and Extrapleural or intrapulmonary catheter placement is readily seen on computed tomography.

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