Clinical presentation and diagnosis of pneumothorax

INTRODUCTION — Gas in the pleural space is termed a pneumothorax. Appropriate treatment of pneumothorax is dictated by the clinical assessment of symptoms, size, and etiology. Thus, prompt recognition and therapy directed at the pneumothorax and its etiology are important to prevent further deterioration.

In this topic review, the clinical presentation and diagnosis of pneumothorax are discussed. The etiology, epidemiology, and treatment of pneumothorax are reviewed in detail separately. (See "Treatment of secondary spontaneous pneumothorax in adults" and "Treatment of primary spontaneous pneumothorax in adults" and "Pneumothorax in adults: Epidemiology and etiology" and "Pneumothorax: Definitive management and prevention of recurrence".)

CLINICAL PRESENTATION — Pneumothorax should be suspected in patients who present with acute dyspnea and chest pain (classically pleuritic), particularly in those with an underlying risk factor (table 1). The major competing diagnoses include acute pulmonary embolism, pleuritis, pneumonia, myocardial ischemia or infarction, pericarditis, and musculoskeletal pain. Routine laboratories, electrocardiography, and chest imaging are usually performed during the diagnostic evaluation process; it is the identification of a pneumothorax on chest imaging that typically differentiates pneumothorax from many of these entities. The evaluation of chest pain and dyspnea are discussed separately. (See "Evaluation of the adult with chest pain in the emergency department" and "Approach to the adult with dyspnea in the emergency department".)

Clinical manifestations — Patients with pneumothorax classically present with the following:

●History – Pneumothorax most often presents with sudden onset of dyspnea and pleuritic chest pain. Since pneumothorax is usually unilateral, the pain is usually felt on the ipsilateral side, but may be central or bilateral in rare cases where pneumothorax is bilateral.

The intensity of dyspnea can range from mild to severe. The severity of the symptoms primarily relates to the volume of air in the pleural space and to the degree of pulmonary reserve, with dyspnea being more prominent if the pneumothorax is large and/or underlying disease is present.

Pneumothorax can present at all ages. Patients with primary spontaneous pneumothorax (PSP; ie, that associated with subpleural blebs in the absence of an underlying disorder) [1] are typically in their early 20s; PSP is rare after age 40 years and classically occurs in young, tall, thin, smoking males. In contrast, since most cases of secondary spontaneous pneumothorax (SSP; ie, that associated with underlying lung disease) are due to emphysema, these patients tend to be older. However, this finding is not absolute; for example, pneumothorax in patients with lymphangioleiomyomatosis or thoracic endometriosis presents in young, nonsmoking females of reproductive age.

Symptoms usually develop when the patient is at rest, although occasionally, pneumothorax develops during exercise, air travel, scuba diving, or illicit drug use. Alternatively, symptoms may occur during or following an invasive procedure or trauma to the chest, neck, gut, or abdomen.

A history of a risk factor or a disorder (table 1) that can be complicated by pneumothorax may be present. (See 'Postdiagnosis evaluation' below.)

●Physical examination – In patients with a small pneumothorax, physical examination findings may not be evident or may be limited to signs of the underlying lung disease, if present. However, characteristic physical findings when a large pneumothorax is present include decreased chest excursion on the affected side, enlarged hemithorax on the affected side, diminished breath sounds, absent tactile or vocal fremitus, and hyperresonant percussion, as well as, rarely, subcutaneous emphysema. Evidence of labored breathing, or accessory muscle use suggest a sizeable pneumothorax or a pneumothorax in a patient with significant underlying lung disease. Tracheal deviation away from the affected side is a late sign but is not always indicative of tension pneumothorax. Hemodynamic compromise (eg, tachycardia, hypotension) is an ominous sign and suggests a tension pneumothorax and/or impending cardiopulmonary collapse.

Some patients with mild or chronic pneumothorax may be asymptomatic and discovered incidentally. For example, among females with lymphangioleiomyomatosis who underwent chest imaging for research purposes after traveling to the National Institutes of Health (NIH), pneumothorax was discovered in 6 percent of females, among which 57 percent were chronic and not associated with new symptoms [2]. (See "Pneumothorax and air travel" and "Sporadic lymphangioleiomyomatosis: Clinical presentation and diagnostic evaluation".)

Patients with pneumothorax on mechanical ventilation (ie, barotrauma) are more likely to present with acute respiratory distress and elevated pressures, the assessment of which is discussed separately. (See "Diagnosis, management, and prevention of pulmonary barotrauma during invasive mechanical ventilation in adults", section on 'Diagnostic evaluation and management' and "Assessment of respiratory distress in the mechanically ventilated patient".)

Laboratory findings — Laboratory findings of pneumothorax are nonspecific but may reveal a mild leukocytosis without left shift. Patients who present with pneumothorax may have routine laboratories performed including D-dimer level and troponin levels to investigate the cause of dyspnea and chest pain. These laboratory tests can be useful for the detection or exclusion of competing etiologies such as myocardial ischemia.

Arterial blood gas — In patients with pneumothorax, peripheral oxygen saturation (SpO₂) may be normal in those without underlying lung disease in whom the pneumothorax is small. However, in patients with sizeable pneumothorax or lung disease, oxygen desaturation is usually evident.

Arterial blood gases are typically obtained when a patient demonstrates tachypnea, accessory muscle use, a pulse oxygen saturation <92 percent, or has a history of hypercapnia. Hypoxemia is common but may be within normal limits if the pneumothorax is small and underlying lung disease is absent. Pneumothorax typically causes an acute respiratory alkalosis particularly when pain, anxiety, and/or hypoxemia are substantial. However, acute hypercapnic respiratory acidosis is unusual because adequate alveolar ventilation can usually be maintained by the contralateral lung, unless underlying disease such as chronic obstructive lung disease (COPD) or cardiovascular compromise is present [3]. In one study of patients with SSP, the arterial oxygen tension (PaO₂) was below 55 mmHg in 17 percent of patients and below 45 mmHg in 4 percent, while the arterial tension of carbon dioxide (PaCO₂) exceeded 50 mmHg in 16 percent and exceeded 60 mmHg in 4 percent [4].

Electrocardiography — Electrocardiographic findings are also nonspecific and may reveal a sinus tachycardia. A more serious rhythm disturbance (eg, bradycardia) may be associated with severe hypoxemia or indicate tension pneumothorax and impending cardiovascular collapse.

DIAGNOSTIC IMAGING — The diagnosis of pneumothorax is a radiologic one. The choice of imaging modality is dependent upon the stability of presentation, the availability of bedside ultrasonography, and the degree of suspicion for competing diagnoses. In general, while those who are unstable should have rapid bedside imaging with pleural ultrasonography, those with a stable presentation can wait for confirmation by chest radiography. Occasionally, chest computed tomography (CT) is required for those in whom the diagnosis is uncertain, those suspected to have a loculated pneumothorax, or stable trauma patients who require CT to assess the extent of other injuries. Incidental pneumothorax may be found on chest CT performed for another reason.

Unstable patients — Hemodynamically unstable patients and patients with severe respiratory distress are typically those with a large or tension pneumothorax, patients with extensive trauma, or patients with significant underlying lung disease. Such patients are resuscitated with the emphasis on stabilization of the airway, breathing, and circulation. Unstable patients should also concomitantly undergo rapid bedside imaging, usually initially with ultrasound, to confirm the diagnosis before undergoing emergent needle or chest tube thoracostomy. In the event that imaging is unavailable or unhelpful, then an empiric decision to place a chest tube without confirmatory imaging should be made on clinical assessment alone. (See 'Pleural ultrasonography' below and "Initial evaluation and management of blunt thoracic trauma in adults", section on 'Primary survey' and "Approach to shock in the adult trauma patient", section on 'Tension pneumothorax'.)

Stable patients — Most patients suspected of having a pneumothorax who are hemodynamically stable and/or not in severe respiratory distress should undergo routine bedside chest radiography in the upright position. Inspiratory and expiratory radiographs have equal sensitivity in detecting pneumothoraces; thus, a standard inspiratory chest radiograph is sufficient in most cases [5]. Chest radiography is useful even in ultrasonography-identified pneumothorax since it can reveal other thoracic abnormalities (eg, lung infiltrates) and the size of a pneumothorax, which, in turn, influences management.

Chest radiography may not be needed if patients are undergoing chest CT for another indication (eg, stable patients with trauma undergoing total body CT for additional injuries or patients with suspected pulmonary embolism undergoing CT pulmonary angiography). In such patients, the CT will readily detect pneumothorax. (See 'Chest computed tomography' below.)

Ultrasonography is being increasingly used in critically ill patients on mechanical ventilation but chest radiography and CT are also frequently used depending upon the severity of presentation. (See "Indications for bedside ultrasonography in the critically ill adult patient" and 'Pleural ultrasonography' below.)

Patients with diagnostic uncertainty — Chest CT is reserved for patients in whom the diagnosis is uncertain following chest radiography (eg, patients with suspected loculated pneumothorax, complicated bullae, or a complex pleural space).

Test performance and interpretation

Chest radiography

Pneumothorax appearance and types — Chest radiography (typically performed in the upright position) is the most common diagnostic imaging modality used for stable patients with suspected pneumothorax. The presence of a pneumothorax is established by demonstrating a white visceral pleural line on the chest radiograph. The visceral pleural line defines the interface between the lung and pleural air (image 1 and image 2). Bronchovascular markings are not typically visible beyond the visceral pleural edge unless the pneumothorax is loculated. The ipsilateral hemithorax size may be increased.

Most pneumothoraces are simple pneumothoraces, whereas although uncommon, true tension pneumothorax is a life-threatening emergency.

●Simple – A simple pneumothorax is one without mediastinal shift to the contralateral side. Patients are clinically and hemodynamically stable, the definition of which is discussed separately. (See "Treatment of primary spontaneous pneumothorax in adults", section on 'Initial evaluation and management'.)

●Tension – A tension pneumothorax arises when air in the pleural space builds up enough pressure to interfere with venous return, leading to hypotension, tachycardia and severe dyspnea. Tension pneumothorax may be seen in approximately 1 to 2 percent of patients [6], likely higher in patients with trauma and patients receiving mechanical ventilation; in the latter group, patients who develop initial signs of pneumothorax are more likely to rapidly progress to cardiovascular collapse than those who are not on mechanical ventilation [7].

Traditional teaching suggested that contralateral shift of the trachea and mediastinum, splaying of the ribs, and flattening of the ipsilateral diaphragm represent radiographic tension. However, these findings may result from atmospheric intrapleural pressure on the side of the pneumothorax while the pleural pressure on the contralateral side remains negative. Clinical evidence of tachycardia, hypotension, and severe dyspnea is more indicative of tension. Conversely, patients may have clinical evidence of tension in the absence of typical radiographic findings of tension. A one-way valve mechanism is responsible for tension pneumothorax allowing gas to enter the pleural space during inspiration but not exit fully during expiration. As gas accumulates, pressure increases within the ipsilateral pleural space resulting in hypotension from reduced venous return, low cardiac output, and respiratory failure due to compression of the contralateral lung. Patients with these findings need immediate attention with needle aspiration or chest tube insertion.

Several other types of pneumothorax can be appreciated on chest radiography:

●Hydropneumothorax – This term is used for patients who have evidence of both fluid and air in the pleural space (eg, trauma patients who have both hemo- and pneumothorax). A hydropneumothorax can be appreciated by the presence of a liquid-gas level when the patient is upright (image 3) and a hazy opacity in a supine patient, that may obscure the pneumothorax (image 4 and image 5) [8].

●Pneumothorax from nonexpandable lung (also called pneumothorax ex vacuo) – Pneumothorax is often seen following pleural fluid removal when the underlying lung fails to expand due to endobronchial obstruction or a thick fibrous pleural rind. Instead of lung re-expansion, gas replaces the pleural space occupied by the effusion. (See "Diagnosis and management of pleural causes of nonexpandable lung" and "Large volume (therapeutic) thoracentesis: Procedure and complications", section on 'Pneumothorax (including pneumothorax ex vacuo)'.)

Most pneumothoraces are unilateral but can be bilateral (also known as simultaneous bilateral spontaneous pneumothoraces):

•Bilateral pneumothoraces may be seen in patients who have a single pleural space. This phenomenon is rare but can be congenital ("buffalo chest"; buffalo only have one thoracic cavity [9]) or iatrogenic in nature following thoracic surgery that disrupts the anterior junction line complex between the right and left thoracic cavities (eg, lung- and heart-transplant recipients, in patients following esophagectomy) [10-14].

•Bilateral pneumothoraces can also present in patients with severe underlying lung disease who have two normal intact pleural spaces that do not communicate with each other (eg, COPD or alpha-1 antitrypsin deficiency, pneumocystis jirovecii, barotrauma from mechanical ventilation, cystic fibrosis, some drugs, metastatic malignancy) [15-21]. However, case reports have described bilateral pneumothoraces in patients without significant lung disease [15,22]. As an example, in one study of 616 cases of primary spontaneous pneumothorax (PSP), 1.6 percent were bilateral; all patients were male with a low body mass index and higher height to body weight ratio compared with patients who had unilateral PSP [22].

Effect of position — Air moves to the least dependent portion of the lung and therefore the radiographic appearance of a pneumothorax depends upon the patient's position:

●In most cases, chest radiography is performed in the upright position and the pneumothorax can be appreciated in the apical or apicolateral position (image 6). It is estimated that only 50 mL of air in the pleural space is needed for the detection of pneumothorax in the upright position [23]. The first rib and clavicle can sometimes interfere with detection of a small pneumothorax in the upright position.

●When the patient is in the supine position (eg, patients who are mechanically ventilated), pleural gas accumulates anteriorly and in a subpulmonic location (image 7 and image 8). This may result in the "deep sulcus" sign (ie, where gas outlines the costophrenic sulcus) (image 9). Rarely, pneumothorax can be visualized in the phrenicovertebral location. In supine patients with pneumomediastinum, a "continuous diaphragm" sign may be evident (ie, where both leaflets of the diaphragm appear as one). It is estimated that approximately 500 mL of air in the pleural space is needed for detection of pneumothorax in the supine position [23].

●For patients in the lateral decubitus position, air rises to the non-dependent lateral location. Only 5 mL of pleural air may be needed to detect pneumothorax in this position [23]. However, imaging in this position may be technically difficult and has largely been supplanted by CT.

Radiologic differential diagnosis — Several conditions can mimic a pneumothorax on the chest radiograph. When in doubt, a chest CT scan may be needed to distinguish these entities:

●Bullae – Subpleural bullae can mimic a loculated pneumothorax (image 10). The distinction is clinically important because the insertion of a chest tube into a bulla can result in iatrogenic pneumothorax and increase the risk for the development of a bronchopleural fistula. Similar to a pneumothorax, bullae have a lateral wall that is convex to the chest wall but unlike pneumothorax, the medial border of a bulla may be appreciated as concave to the chest wall (image 11 and image 12A-B) [24].

●Skin folds – Skin folds (eg, due to obesity or distortion of the skin by the imaging cassette) may mimic pneumothorax. However, skin folds frequently demonstrate a line (mistakenly interpreted as the visceral pleural line) that when followed, extends beyond or ends just before the rib cage. Other findings include an increase in opacification, which ceases at the distal edge of the skin fold, and the presence of visible bronchovascular markings beyond the skinfold line. Classically, the edge of the skinfold appears as a black "Mach band" instead of a thin white pleural line typical of pneumothorax (image 13 and image 14).

●Gastric herniation – Herniation of the stomach into the chest (eg, due to diaphragmatic rupture) can mimic the appearance of a left-sided pneumothorax (image 15) and, if a chest tube is inserted, can result in viscus perforation. Intrathoracic stomach air can be hard to distinguish from pneumothorax but the presence of loops of bowel in the left hemithorax is supportive of gastric herniation.

Pneumothorax size — Several methods are available to assess the size of pneumothorax none of which are highly accurate or superior, and many tend to underestimate or overestimate the size [25]. Such inaccuracy may result when the assessment of size uses a one- or two-dimensional measurement that does not accurately reflect the three-dimensional nature of the pleural space; in addition, such measurements also assume that the lung collapses uniformly, which is not always the case. Despite available methods, considerable variation in practice exists and many clinicians use gestalt assessment of size in conjunction with symptoms to make management decisions. (See "Treatment of secondary spontaneous pneumothorax in adults", section on 'Management strategy' and "Treatment of primary spontaneous pneumothorax in adults", section on 'Stable patients'.)

Some of the available methods for size assessment, none of which are perfect, include the following:

●British Thoracic Society (BTS) guidelines – Updated 2023 BTS guidelines place less emphasis on size than the previous 2010 guidelines [26]. We prefer to incorporate both size and symptoms when assessing patients with pneumothorax for treatment.

Size assessment for PSP in the United States typically uses a cutoff of ≥3 cm between the pleural line and the chest wall at the level of the apex on a chest radiograph to distinguish a large from a small pneumothorax [27] while, in Europe, physicians use a cutoff of ≥2 cm at the level of the hilum [28]. A distance of 2 cm roughly correlates with a 50 percent pneumothorax, which is considered a large pneumothorax [28]. However, there is poor agreement in size classification between these two approaches, resulting in discrepancies in management [29,30]. Estimation of size is usually only performed on chest radiography (and, less commonly, chest CT). Ultrasonography cannot reliably quantify pneumothorax size. (See "Treatment of primary spontaneous pneumothorax in adults" and "Treatment of secondary spontaneous pneumothorax in adults".)

●The average interpleural distance (AID) – The AID is the sum of the distances between the ribs and the visceral pleura at the apex, mid-thorax, and base of the lung (in millimeters), divided by three to estimate pneumothorax size as a percentage of the hemithorax volume (figure 1 and image 16). This is also called the Rhea method [31].

●The Collins method – The Collins method [32] is similar to the Rhea method. Direct comparisons of both methods have shown high level of agreements [33].

●Formulas – The size of a pneumothorax can be measured using the Light Index [31,34]:

Percent pneumothorax = 100 – [(average lung diameter³/average hemithorax diameter³) x 100]

Using the Light index, one study found strong correlation with the volume of air removed [34], while another found poor correlation with CT volumetrics [25].

Most of these assessments are made on chest radiographs. However, CT is likely the most accurate modality to assess size. Newer CT-based measurements of the ratio of lung volume to hemithorax volume may hold promise [35]. Ultrasonography is not typically used to assess pneumothorax size.

The use of size to determine the therapeutic strategy is discussed separately. (See "Treatment of primary spontaneous pneumothorax in adults", section on 'Initial evaluation and management' and "Treatment of secondary spontaneous pneumothorax in adults", section on 'Initial management of first event'.)

Pleural ultrasonography — Ultrasound of the pleura is best utilized when bedside rapid imaging is needed to make the diagnosis of pneumothorax (eg, unstable patients with trauma, or patients with suspected tension) because ultrasound has been shown to be sensitive diagnostically [36-46] and ultrasonography is more readily available with shorter wait times than for bedside chest radiography [47]. It is also typically used for suspected pneumothorax that follows ultrasound-guided procedures (eg, thoracentesis or central venous catheterization) and is being increasingly used in critically ill patients. (See "Indications for bedside ultrasonography in the critically ill adult patient", section on 'Thoracic ultrasonography' and "Emergency ultrasound in adults with abdominal and thoracic trauma", section on 'Pneumothorax and hemothorax' and "Bedside pleural ultrasonography: Equipment, technique, and the identification of pleural effusion and pneumothorax" and "Initial evaluation and management of penetrating thoracic trauma in adults", section on 'E-FAST'.)

The presence of a lung point on pleural ultrasonography is diagnostic of pneumothorax (movie 1). In partially deflated lung, the lung point is the intermittent and respirophasic observation of lung sliding at the boundary between the pneumothorax (where there is no apposition of the pleura, so no lung sliding is seen) and the partially inflated lung (where there is still apposition of the two pleural surfaces, so lung sliding is seen). A pneumothorax is also suggested if lung sliding (movie 2 and movie 3) and/or lung pulse is absent. However, a lung point may not always be present (eg, complete deflation of the lung) and the absence of lung sliding or lung pulse is not specific, since it can be seen in other conditions. Thus, a chest radiograph is always advisable. If ultrasonography shows a pneumothorax, a chest radiography will help estimate the size of a pneumothorax. If ultrasonography is negative, a chest radiograph is important to assess for other causes of the patient's presenting complaint(s).

Several studies indicate that ultrasonography may be superior to standard chest radiography for the detection of pneumothorax [36-46,48]. Several meta-analyses of mostly observational studies reported sensitivities of ultrasound that were superior to chest radiography (79 to 91 percent versus 40 to 50 percent) [45,46,49]. However, there was significant heterogeneity among different populations studied; in addition, the sensitivity of chest radiography may have been underestimated due to the high frequency of supine chest radiographs in many of the studies.

False-positives of pneumothorax can occur with ultrasonography especially in patients with underlying diseases (eg, emphysema) [50].

Imaging of pneumothorax on ultrasonography is discussed in more detail separately. (See "Bedside pleural ultrasonography: Equipment, technique, and the identification of pleural effusion and pneumothorax", section on 'Evaluation for pneumothorax'.)

Chest computed tomography — Chest CT is the best modality for determining the presence, size, and location of intrapleural gas (image 17) [42]. Small amounts of air in the pleural space and pleural pathology including pleural effusions and adhesions as well as loculations can be better appreciated by CT than chest radiography (image 18 and image 19 and image 20 and image 21).

Based upon its superior resolution and observational studies, chest CT is considered more accurate than either chest radiography [51,52] or ultrasonography [42] for the diagnosis of pneumothorax. CT can readily distinguish gas from other structures including the lung parenchyma, the pleural membranes, and the mediastinum, making it the modality of choice when diagnostic doubt exists.

POSTDIAGNOSIS EVALUATION — Following initial diagnosis and management, additional steps need to be taken to identify a potential etiology(s) for pneumothorax. For many patients with pneumothorax, an underlying cause (eg, trauma or iatrogenic) may be evident or an underlying lung disorder (eg, chronic obstructive lung disease [COPD], interstitial lung disease, lung cancer, infection) may be known at the time of presentation. In others, pneumothorax may be the first manifestation of an unknown disorder (eg, catamenial pneumothorax, lymphangioleiomyomatosis [LAM], Birt-Hogg-Dubé syndrome). The approach outlined below is based upon our experience since there are no guidelines or data to help guide the clinician in this matter.

Patients with a clear cause — In many cases, the etiology is evident from the history, examination, and chest radiography or chest CT findings. For example, patients in this category would include those with trauma-related pneumothorax, procedural-related pneumothorax (eg, following central venous catheterization, percutaneous lung biopsy), or patients with a lung disorder known to be associated with pneumothorax (eg, COPD, cystic fibrosis, malignancy, LAM, pneumocystis pneumonia). In such cases, no additional testing is typically required unless a second disorder is suspected.

Patients without a clear cause — In some cases, the pneumothorax may not have an apparent cause and clinicians need to decide how much testing should be performed to identify a cause. After initial therapy, these patients should be re-evaluated with another detailed history and examination and with re-examination of chest imaging to identify abnormalities that may have been missed during the initial assessment. In many instances, this re-evaluation is performed after initial therapy and discharge and may prompt noncontrast high resolution chest CT (HRCT), if not already performed, as well as pulmonary function testing. Additional testing may be subsequently targeted at specific suspected etiologies. (See "Treatment of primary spontaneous pneumothorax in adults" and "Treatment of secondary spontaneous pneumothorax in adults".)

Clinical re-evaluation — Clinical re-evaluation should consider but not be limited to the following:

●Chest pain or hemoptysis perimenstrually in a young female with or without a history of endometriosis might suggest catamenial pneumothorax. (See "Clinical features, diagnostic approach, and treatment of adults with thoracic endometriosis".)

●A family history of pneumothorax may suggest inheritable disorders such as alpha-1 antitrypsin deficiency or Birt-Hogg-Dubé syndrome, and rarely Marfan or Ehlers Danlos syndrome. A personal or family history of renal cancer may also support Birt-Hogg-Dubé syndrome. (See "Clinical manifestations, diagnosis, and natural history of alpha-1 antitrypsin deficiency" and "Birt-Hogg-Dubé syndrome" and "Clinical manifestations and diagnosis of Ehlers-Danlos syndromes" and "Genetics, clinical features, and diagnosis of Marfan syndrome and related disorders".)

●A history of travel (eg, to regions where tuberculosis is endemic) or reason to suspect underlying human immune deficiency disorder may be sought in those with a possible infectious reason for pneumothorax. (See "Pulmonary tuberculosis: Clinical manifestations and complications" and "Acute and early HIV infection: Clinical manifestations and diagnosis" and "Screening and diagnostic testing for HIV infection".)

●A joint and skin examination may reveal dry eye and joint disease suggestive of Sjögren's disease (which can be complicated by lung cysts), joint hypermobility or hyperextensible skin consistent with Ehlers Danlos syndrome, or pectus carinatum and disproportionate tall stature to suggest Marfan syndrome. (See "Diagnosis and classification of Sjögren’s disease" and "Clinical manifestations and diagnosis of Ehlers-Danlos syndromes" and "Genetics, clinical features, and diagnosis of Marfan syndrome and related disorders".)

●A detailed drug history or track marks may suggest illicit drug use or identify immunosuppressant drugs not previously suspected as an etiology of pneumothorax. (See "Substance use disorders: Clinical assessment" and "Testing for drugs of abuse (DOAs)".)

●A history of weight loss or sweats may suggest occult malignancy. (See "Approach to the patient with unintentional weight loss".)

●A detailed social history may identify recent air travel or scuba diving as a hobby. (See "Pneumothorax and air travel" and "Complications of SCUBA diving".)

●Any lucencies or nodules on chest radiography in a young smoking male or nonsmoking female should prompt CT chest imaging to look for evidence of Langerhans cell histiocytosis (LCH), subpleural blebs, or LAM. (See "Pulmonary Langerhans cell histiocytosis" and "Sporadic lymphangioleiomyomatosis: Clinical presentation and diagnostic evaluation".)

●Cysts identified on CT should prompt a diagnostic evaluation for cystic lung disorders. (See "Diagnostic approach to the adult with cystic lung disease".)

Additional testing

Chest computed tomography — In the majority of cases, the diagnosis of pneumothorax is made on chest radiography. If not already performed, a proportion of patients additionally need chest CT when a specific etiology is suspected or the underlying etiology remains unknown. We typically perform CT in the following:

●Patients with abnormalities on their chest radiograph (eg, lucencies that suggest cysts, bullae that suggest emphysema), or on clinical evaluation (eg, clubbing, hemoptysis, systemic symptoms, or basal crackles) that suggest an underlying lung disorder.

●Patients with a suspected etiology for pneumothorax, which may be more readily identified on CT. For example, chest CT in:

•A young smoking male may reveal subpleural blebs or nodules or cysts consistent with LCH. (See "Pulmonary Langerhans cell histiocytosis" and "Sporadic lymphangioleiomyomatosis: Clinical presentation and diagnostic evaluation" and "Clinical features, diagnostic approach, and treatment of adults with thoracic endometriosis".)

•A young non-smoking female may reveal cysts consistent with LAM or pleural and parenchymal abnormalities that suggest thoracic endometriosis. (See "Pulmonary Langerhans cell histiocytosis" and "Sporadic lymphangioleiomyomatosis: Clinical presentation and diagnostic evaluation" and "Clinical features, diagnostic approach, and treatment of adults with thoracic endometriosis".)

Screening young females with a first spontaneous pneumothorax with chest CT for underlying cysts is controversial. While some clinicians avoid chest CT screening in this population based upon the premise that the incidence of pathology is too low, we advocate having a low threshold to perform chest CT in young (25 to 54 year) nonsmoking females, in whom the prevalence of LAM, for example, is estimated to be approximately 5 percent [53,54].

•A cigarette smoker of over 20 pack years, marijuana smoker, or user of illicit drugs may reveal emphysema, bullous disease, or malignancy. (See "High resolution computed tomography of the lungs" and "Overview of pulmonary disease in people who inject drugs", section on 'Pneumothorax and pneumomediastinum'.)

•A young adult with a family history of pneumothorax, skin lesions, or kidney tumors may reveal lung cysts consistent with Birt-Hogg-Dubé syndrome. (See "Birt-Hogg-Dubé syndrome".)

●Patients with a history of previous pneumothorax or prolonged air leak on chest tube drainage where chest CT may reveal underlying cysts or other pathologies that may prompt additional testing. (See "Diagnostic approach to the adult with cystic lung disease".)

●Patients with unusual etiologies for pneumothorax (eg, drugs, anorexia, exercise) in whom more serious pathologies need to be excluded. (See "Overview of pulmonary disease in people who inject drugs", section on 'Pneumothorax and pneumomediastinum' and "Anorexia nervosa in adults and adolescents: Medical complications and their management", section on 'Pulmonary' and "The benefits and risks of aerobic exercise".)

●Patients with ongoing air leak and/or requiring surgery (as preoperative workup).

Lung function tests — Pulmonary function tests (PFTs) are not routinely performed and are not valuable at the time of diagnosis or during treatment. However, PFTs may be performed after recovery (eg, weeks) when underlying lung disease (eg, asthma, COPD, LCH, LAM) is suspected. PFTs should be performed in stable patients and are not helpful in those in whom a chest tube is in place or in whom pleurodesis has been recently performed.

Other etiology-specific testing — Additional tests are performed when specific etiologies are being considered based upon clinical and radiologic re-evaluation (table 1). These might include genetic testing for suspected inheritable syndromes (eg, alpha-1 antitrypsin deficiency, Birt-Hogg-Dubé, Ehlers Danlos syndrome, Marfan syndrome), vascular endothelial growth factor-D for suspected LAM, and serologic testing for suspected Sjögren's disease.

Lung biopsy is rarely performed for suspected interstitial lung disease or malignancy. However, when pleurodesis is being considered for pneumothorax, many surgeons also take tissue for occult conditions that are not easily detected clinically.

When infection is suspected, microbiologic, serologic testing, and/or bronchoscopy with bronchoalveolar lavage may also be required.

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Pneumothorax".)

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

●Basics topic (see "Patient education: Pneumothorax (collapsed lung) (The Basics)")

PATIENT PERSPECTIVE TOPIC — Patient perspectives are provided for selected disorders to help clinicians better understand the patient experience and patient concerns. These narratives may offer insights into patient values and preferences not included in other UpToDate topics. (See "Patient perspective: Lymphangioleiomyomatosis (LAM)".)

SUMMARY AND RECOMMENDATIONS

●Clinical presentation – Pneumothorax (gas in the pleural space) should be suspected in patients with acute dyspnea and pleuritic chest pain, particularly when an underlying risk factor is present (table 1). (See 'Clinical presentation' above.)

•While young, thin, smoking males are more likely to have primary spontaneous pneumothorax (PSP; ie, that associated with subpleural blebs in the absence of an underlying disorder) and older patients are more likely to have secondary pneumothorax (SSP; ie, as a complication of an underlying lung disorder), this division is not absolute and underlying disorders are not always readily apparent. (See 'Clinical manifestations' above.)

•Laboratory and electrocardiography findings are nonspecific. (See 'Laboratory findings' above and 'Electrocardiography' above.)

•Arterial blood gas analysis may be normal but classically reveals hypoxemia and a respiratory alkalosis; acute hypercapnic respiratory acidosis can occur rarely and is an ominous sign. (See 'Arterial blood gas' above.)

●Diagnostic imaging – The diagnosis of pneumothorax is a radiologic one that is mostly made in the context of an evaluation for competing diagnoses (eg, acute pulmonary embolism, pleuritis, pneumonia, myocardial ischemia or infarction, pericarditis, and musculoskeletal pain). The imaging modality of choice is dependent upon the stability of presentation, the availability of bedside ultrasonography, and the degree of suspicion for competing diagnoses:

•Bedside pleural ultrasonography (if available) – For patients with suspected pneumothorax who are hemodynamically unstable or in severe respiratory distress, we suggest rapid bedside imaging with pleural ultrasonography, if available, with ongoing resuscitation efforts focused on stabilizing the airway, breathing, and circulation. The presence of a lung point on pleural ultrasonography is diagnostic of pneumothorax (movie 1). A pneumothorax is also suggested if lung sliding (movie 2 and movie 3) and/or lung pulse is absent but false positives can occur. In the event that ultrasonography is unavailable or unhelpful, then an empiric decision to place a chest tube without confirmatory imaging should be made on clinical assessment alone. (See 'Unstable patients' above and 'Pleural ultrasonography' above and "Approach to shock in the adult trauma patient", section on 'Tension pneumothorax'.)

•Bedside chest radiography – For most stable patients with suspected pneumothorax, we suggest bedside chest radiography in the upright position unless chest CT is planned for another indication or bedside ultrasonography and experts in its interpretation are readily available (eg, following a procedure, patients who are mechanically ventilated). On chest radiography, the presence of a pneumothorax is established by demonstrating a white visceral pleural line on the chest radiograph that is typically convex towards the chest wall (image 22 and image 2). However, imaging characteristics vary with position. (See 'Stable patients' above and 'Chest radiography' above.)

•Chest CT – For patients in whom the diagnosis is uncertain following chest radiography (eg, patients with suspected loculated pneumothorax, complicated bullae, complex pleural space), we suggest chest CT. Chest CT is the most accurate method available for detection of pneumothorax based upon its superior ability to distinguish gas from other structures including the lung parenchyma, the pleural membranes, and the mediastinum. (See 'Patients with diagnostic uncertainty' above and 'Chest computed tomography' above.)

●Investigating the underlying etiology – For many patients with pneumothorax, an underlying cause (eg, trauma or iatrogenic) or underlying lung disorder (eg, chronic obstructive lung disease [COPD]) (table 1) is evident at the time of presentation and, in such cases, no additional testing is typically required unless a second disorder is suspected. However, in some cases the pneumothorax may not have an apparent cause. After initial therapy, such patients should be re-evaluated with another detailed history and examination; chest imaging should also be re-examined with a low threshold to perform a high resolution chest CT (if not already performed) with or without pulmonary function testing. If necessary, additional testing (eg, alpha-1 antitrypsin level testing, genetic testing for Birt-Hogg-Dubé) may be subsequently specifically targeted at suspected etiologies. (See 'Postdiagnosis evaluation' above.)

ACKNOWLEDGMENTS

The UpToDate editorial staff acknowledges Patricia Tietjen, MD, who contributed to earlier versions of this topic review.

The UpToDate editorial staff also acknowledges Richard W Light, MD (deceased), who contributed to earlier versions of this topic.