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Walif Chbeir: Medical Imaging of PneumoThorax (PNO)–1


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

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Walif Chbeir: Medical Imaging of PneumoThorax (PNO)–1

  1. 1. Edited March02,2016 Medical Imaging of PneumoThorax (PNO1) Dr WALIF CHBEIR * We searched Medline and google for articles relating to Pneumothorax with focus on imaging appearances and diagnostic approach. * Key Words: - Pneumothorax/etiology. - Pneumothorax/radiography. - Pneumothorax/ultrasonography. - Pneumothorax/diagnosis. - Acute respiratory distress syndrome (ARDS) - Tension Pneumothorax - intensive care unit (ICU)- mechanical ventilation. - critical care * No financial relationships with commercial entities to disclose. I- Definition PNO is air in the pleural space causing partial or complete lung collapse. II-Etiology * Primary spontaneous pneumothorax (PSP) occurs in patients without underlying pulmonary disease. It is thought to be due to spontaneous rupture of subpleural apical blebs or bullae that result from smoking or that are inherited. * Secondary spontaneous pneumothorax (SSP) It most often results from rupture of a bleb or bulla in patients with underlying pulmonary disease. SSP is more serious than PSP because it occurs in patients whose underlying lung disease decreases their pulmonary reserve. --Most common: - Chronic obstructive pulmonary disease
  2. 2. - Asthma - Cystic fibrosis - Pneumonia: Pneumocystis jirovecii infection / Tuberculosis / Bacterial pneumonia.( Cavitary or Necrotizing) . - ARDS -- Less common: - About 0.5% of pneumothoraces are associated with lung metastases, of which 89% are caused by sarcomas, with osteogenic sarcoma being the most common - Langerhans cell histiocytosis - Lymphangioleiomyomatosis/tuberous sclerosis . - Sarcoidosis. - Connective tissue disorders: Ankylosing spondylitis , Ehlers-Danlos syndrome, Marfan syndrome, Polymyositis and dermatomyositis, RA, Systemic sclerosis. - Catamenial pneumothorax: is a rare form of SSP that occurs within 48 h of the onset of menstruation in premenopausal women and sometimes in postmenopausal women taking estrogen . The cause is intrathoracic endometriosis, possibly due to migration of peritoneal endometrial tissue through diaphragmatic defects or embolization through pelvic veins. * Traumatic pneumothorax is a common complication of penetrating or blunt chest injuries. - In patients with penetrating wounds that traverse the mediastinum,or with severe blunt trauma, pneumothorax may be caused by disruption of the tracheobronchial tree. Air from the pneumothorax may enter the soft tissues of the chest and/or neck (subcutaneous emphysema), or mediastinum (pneumomediastinum). - Iatrogenic pneumothorax is caused by medical interventions, including transthoracic needle aspiration and Biopsy, thoracentesis, Thoracotomy, central venous catheter placement, mechanical ventilation and barotrauma, and cardiopulmonary resuscitation. Also: Surgical procedures in the thorax, head, or neck. and Abdominal procedures using bowel or peritoneal distension. III- Symptoms and Signs ( + PhysioPatho) * Small pneumothoraces are occasionally asymptomatic. * Symptoms of pneumothorax typically include pleuritic chest pain and shortness of breath. - Dyspnea may be sudden or gradual in onset depending on the rate of development and size of the pneumothorax.
  3. 3. - Pain can simulate pericarditis, pneumonia, pleuritis, pulmonary embolism, musculoskeletal injury (when referred to the shoulder), or an intra-abdominal process (when referred to the abdomen). Pain can also simulate cardiac ischemia, although typically the pain of cardiac ischemia is not pleuritic. - Physical findings classically consist of absent tactile fremitus, hyperresonance to percussion, and decreased breath sounds on the affected side. If the pneumothorax is large, the affected side may be enlarged with the trachea visibly shifted to the opposite side. With tension pneumothorax, hypotension can occur. . Importantly, the volume of the pneumothorax can show limited correlation with the intensity of the symptoms experienced by the victim, and physical signs may not be apparent if the pneumothorax is relatively small. * Primary Spontaneous Pneumothorax (PSP) : - Classically in tall, thin, asthenic men. Most patients are between 20 and 40 years of age, and the male-to-female ratio is approximately 5 to 1. It is thought to be due to spontaneous rupture of subpleural apical blebs or bullae that result from smoking or that are inherited. It generally occurs at rest, although some cases occur during activities involving reaching or stretching. PSP also occurs during diving and high-altitude flying . - It usually causes limited symptoms. Chest pain and sometimes mild breathlessness are the usual predominant presenting features. People who are affected by PSPs are often unaware of potential danger and may wait several days before seeking medical attention. PSPs more commonly occur during changes in atmospheric pressure, explaining to some extent why episodes of pneumothorax may happen in clusters. It is rare for PSPs to cause tension pneumothoraces. * Secondary Spontaneous Pneumothorax: Symptoms in SSPs tend to be more severe than in PSPs, as the unaffected lungs are generally unable to replace the loss of function in the affected lungs. Hypoxemia is usually present and may be observed as cyanosis. Hypercapnia is sometimes encountered; this may cause confusion and if very severe may result in comas. The sudden onset of breathlessness in someone with COP), cystic fibrosis, or other serious lung diseases should therefore prompt investigations to identify the possibility of a pneumothorax. * Traumatic pneumothorax (TP) Traumatic pneumothoraces have been found to occur in up to half of all cases of chest trauma, with only rib fractures being more common in this group. The pneumothorax can be occult (not readily apparent) in half of these cases, but may enlarge particularly if mechanical ventilation is required. They are also encountered in patients already receiving mechanical ventilation for some other reason.
  4. 4. - Many patients also have a hemothorax (hemopneumothorax). - In patients with penetrating wounds that traverse the mediastinum or with severe blunt trauma, pneumothorax may be caused by disruption of the tracheobronchial tree. - Air from the pneumothorax may enter the soft tissues of the chest and/or neck (subcutaneous emphysema), or mediastinum (pneumomediastinum). - Patients commonly have pleuritic chest pain, dyspnea, tachypnea, and tachycardia. - Breath sounds may be diminished and the affected hemithorax hyperresonant to percussion—mainly with larger pneumothoraces. However, these findings are not always present and may be hard to detect in a noisy resuscitation setting. - Subcutaneous emphysema causes a crackle or crunch when palpated; findings may be localized to a small area or involve a large portion of the chest wall and/or extend to the neck; extensive involvement suggests disruption of the tracheobronchial tree. - Air in the mediastinum may produce a characteristic crunching sound synchronous with the heartbeat (Hamman sign or Hamman crunch), but this finding is not always present and also is occasionally caused by injury to the esophagus. * Open pneumothorax - Some patients with traumatic pneumothorax have an unsealed opening in the chest wall. when the opening is sufficiently large, the ventillation on the affected side is eliminated respiratory mechanics are impaired and the inability to ventilate the lungs causes respiratory distress and respiratory failure. * Tension pneumothorax ( TP) is accumulation of air in the pleural space under pressure, compressing the lungs and decreasing venous return to the heart. Although multiple definitions exist, a tension pneumothorax is generally considered to be present when a pneumothorax leads to significant impairment of respiration and/or blood circulation. - Tension pneumothorax develops when a lung or chest wall injury is such that it allows air into the pleural space but not out of it (a one-way valve). As a result, air accumulates and compresses the lung, eventually shifting the mediastinum, compressing the contralateral lung, and increasing intrathoracic pressure enough to decrease venous return to the heart, causing shock. These effects can develop rapidly, particularly in patients undergoing positive pressure ventilation.
  5. 5. - Causes include patients receiving positive-pressure ventilation (most commonly) with mechanical ventilation or particularly during resuscitation, failed central venous cannulation, simple (uncomplicated) pneumothorax with lung injury that fails to seal following penetrating or blunt chest trauma and in patients with lung disease. - Symptoms and signs initially are those of simple pneumothorax, tachypnea and increased heart rate . As intrathoracic pressure increases, patients develop hypotension, tracheal deviation, neck vein distention and respiratory distress. The affected hemithorax is hyperresonant to percussion with reduced expansion and often feels somewhat distended, tense, and poorly compressible to palpation. Rarely, there may be cyanosis, altered level of consciousness. - Recent studies have shown that the development of tension features may not always be as rapid as previously thought. Deviation of the trachea to one side and the presence of raised jugular venous pressure (distended neck veins) are not reliable as clinical signs. - In case of Tension pneumothorax occuring in someone who is receiving mechanical ventilation, it may be difficult to spot as the person is typically receiving sedation; it is often noted because of a sudden deterioration in condition. - This is a medical emergency and may require immediate treatment without further investigations. Without appropriate treatment, the impaired venous return can cause systemic hypotension and respiratory and cardiac arrest (pulseless electrical activity) within minutes. * Acute respiratory distress syndrome, critically ill adults and pneumothorax: - pneumothorax is common in ventilated critically ill patients . Approximately 50% of patients with ARDS who require mechanical ventilation will develop a pneumothorax during their treatment. The ARDS damages the lung parenchyma, and the high intrathoracic pressures resulting from mechanical ventilation of stiff lungs contributes to rupture of the diseased lung tissue. - In patients with minimal pulmonary reserve, even a small pneumothorax can have adverse hemodynamic effects or cause tension that rapidly induces cardiovascular collapse and death. - Many factors may precipitate the occurrence of pneumothorax in ARDS, such as the mechanical ventilation settings, the clinical severity of ARDS and the underlying pulmonary pathology (like preexisting emphysema).
  6. 6. - Up to 96% of patients who develop pneumothorax while receiving ventilation will progress to tension pneumothorax because the machine blows air out of the hole in the lung into the pleural space with positive pressure. - Tension pneumothorax occurs when intrapleural pressure exceeds atmospheric pressure. Tension pneumothorax is a clinical diagnosis, not a radiographic diagnosis, because the respiratory and hemodynamic consequences of tension pneumothorax do not have radiographic equivalents in many circumstances. . Radiographic signs of tension (mediastinal shift, inversion of diaphragm, enlargement of affected hemithorax) can occur in the absence of adverse physiologic effects, and the physiologic effects of pleural tension may be present without radiographic signs of tension. In ARDS, the diseased noncompliant lung may not collapse in the presence of a pneumothorax, and the controralateral lung may be too stiff to allow mediastinal shift. Thus, tension pneumothorax in ARDS can present as a loculated paracardiac or subpulmonic air collection with little or no mediastinal shift and only slight changes of the cardiac contour. ++++ . Also, In patients with severe ARDS and pleural adhesions, most if not all of cardinal clinical signs of Tension PNO (sudden increase in ventilation pressures, severely reduced breath sounds on the affected side, jugular venous distention, and the dreaded mediastinal shift) that results in cardiovascular collapse will be absent. The lung may be so diseased, stiff and noncompliant that it does not fully collapse when air trapped in the pleural space presses on it. If only a small portion of the lung is externally compressed, the mediastinum will not be affected Therefore, radiographic evidence of extrapulmonary air collections becomes even more important in this group of critically ill patients. . Adherence of inflamed pleura to the chest wall ( parietal pl) may confine a pneumothorax to a loculated portion of the pleural space around the site of the air leak. Even daily chest radiographs can miss small loculated pneumothoraces. Two studies reported by Chon and colleagues (cf num ref) reported that in critically ill, mechanically ventilated adults, 33% to 50% of "missed" pneumothoraces (that is, pneumothoraces too small or subtle to be seen on the radiograph until retrospective review) progressed to tension. Even small areas of compression on the lung can have a significant impact on pulmonary function when the lungs are so dysfunctional to begin with. - The most repeatable finding of PNO in patients with severe ARDS was a subtle drop in oxygenation measurements. Patients showed an improvement in PaO2 within 24 hours of chest tube insertion and pneumothorax resolution.
  7. 7. . Loculated pneumothorax provides only subtle clinical clues. The only clinical evidence may be deteriorating oxygenation without another obvious cause. . The early and accurate diagnosis of pneumothorax in ARDS patients is mandatory since this complication carries an increased mortality. Furthermore, small pneumothoraces in these patients can cause severe hemodynamic or pulmonary compromise. This is the reason why pneumothorax must always be suspected in any patient with ARDS who experiences an acute worsening in respiratory function, accompanied with dyspnea and hypoxemia, which is usually unresponded to oxygen therapy. . Although non-specific, the association of respiratory and haemodynamic signs found with a tension pneumothorax are a medical emergency. Severe haemodynamic compromise will require urgent needle decompression of the pneumothorax before its diagnosis being confirmed radiologically. Fortunately this situation is uncommon and there is frequently time for radiological investigations to help establish the diagnosis of a simple pneumothorax. * Complications of PNO - In most reported series, the rate of recurrence of spontaneous pneumothorax on the same side is as much as 30%. - On the contralateral side, the rate of recurrence is approximately 10%. - Other complications include the following: Reexpansion pulmonary edema . Bronchopleural fistula Occurs in 35% of patients, Pneumomediastinum and pneumopericardium and Tension pneumothorax. Tension PNO may occur after spontaneous pneumothorax, although it is more common after traumatic pneumothorax or with mechanical ventilation. * In summary: A simple unilateral pneumothorax, even when large, is well tolerated by most patients unless they have significant underlying pulmonary disease. However, tension pneumothorax can cause severe hypotension, and open pneumothorax can compromise ventilation.