Version May 2024
INTRODUCTION — Portable ultrasonography devices are used at the bedside to evaluate pleural abnormalities and to guide thoracentesis and related procedures such as pleural drainage, catheter placement, and needle aspiration biopsy of pleural or subpleural lung masses.
The equipment, technique, and common imaging abnormalities related to pleural ultrasonography will be reviewed here. Our approach is similar to that issued by the European Respiratory Society [1]. The diagnostic evaluation and imaging of a pleural effusion and the technique of diagnostic thoracentesis are discussed separately. (See "Pleural fluid analysis in adults with a pleural effusion" and "Diagnostic evaluation of the hemodynamically stable adult with a pleural effusion" and "Imaging of pleural effusions in adults" and "Ultrasound-guided thoracentesis".)
CHOOSING BEDSIDE VERSUS CONSULTATIVE ULTRASOUND — Point-of-care pleural ultrasonography is performed at the bedside by clinicians trained in its performance and interpretation using inexpensive portable equipment [2-4]. In contrast, consultative pleural ultrasonography is performed in a radiology suite using larger, non-portable, expensive equipment. When pleural ultrasonography is performed by the radiology service, skilled ultrasonography technicians obtain the images which are subsequently interpreted by the radiologist, thereby contributing to delay in diagnosis. Given the cost savings, time efficiency, convenience, accuracy, and clinical applications of bedside pleural ultrasonography, it is often chosen by pulmonologists trained in its use as the preferred imaging modality for rapid bedside imaging of the pleura. Bedside pleural ultrasonography has several advantages including the following:
●Point-of-care use – Bedside pleural ultrasonography permits real-time scanning for procedural guidance and for immediate integration of the results into a management plan [5].
●Image guidance for pleural procedures – In patients undergoing thoracentesis, including those on ventilatory support, ultrasonography is associated with a lower rate of complications, particularly pneumothorax, when compared with patients who undergo thoracentesis without image guidance. Further details are provided separately. (See "Ultrasound-guided thoracentesis".)
Bedside pleural ultrasonography is an effective means of guiding pleural interventional procedures such as empyema drainage and aspiration/biopsy of pleural-based lesions [6]. However, computed tomography (CT) guidance may be required in cases where patient-specific factors such as obesity, chest wall dressings, or massive edema degrade ultrasonography image quality. (See "Imaging of pleural effusions in adults", section on 'Computed tomography'.)
●Detection of pleural pathology – Ultrasound examination of the pleura is more sensitive than chest radiography at detecting the presence of pleural fluid and differentiating pleural fluid from lung consolidation in the critically ill patient [7]. Compared with CT, pleural ultrasonography has a 95 percent sensitivity for the detection of pleural fluid in patients with a "white out" on plain chest radiograph, but is slightly less sensitive in detecting small amounts of fluid [8,9]. Ultrasonography is also superior in detecting pleural effusion septations as well as differentiating pleural fluid from chest wall tumor invasion, pleural thickening, and pleural masses compared with chest CT scan [10,11]. (See "Indications for bedside ultrasonography in the critically ill adult patient".)
●Reduced cost and radiation exposure – Bedside ultrasonography is more cost efficient as it is performed at the bedside with a low-cost multipurpose ultrasound machine. Ultrasonography uses no ionizing radiation, unlike chest radiography and chest CT.
EQUIPMENT — A wide variety of portable ultrasound machines with two-dimensional scanning capability are used for bedside pleural ultrasonography and associated procedures [10,12].
Transducers — A 3.5 MHz phased array ultrasonography probe is preferred for pleural imaging (picture 1 and movie 1 and picture 2). This probe is designed for echocardiography and has a small footprint to facilitate scanning between rib interspaces. The phased array probe is a multipurpose device that can be used for pleural, lung, and abdominal imaging (the latter by using the abdominal preset that is standard in newer generation portable machines). The phased array probe has sufficient depth of penetration to image structures deep within the thorax, unlike the linear high frequency probe that is has superior resolution but limited penetration. The curvilinear convex abdominal probe may be used, if no phased array multipurpose cardiac probe is available.
For detailed visualization of the pleural surface morphology, a linear higher frequency 7.5 MHz ultrasonography probe is required (picture 2). Compared with the cardiac probe, this vascular probe has superior resolution but limited penetration. It is used specifically for imaging the pleural surface in order to detect pleural surface irregularity, lung point, and centromeric consolidations (see 'Chest wall' below). It cannot be used to image deeper structures within the thorax (eg, the lung).
Doppler is generally not required for pleural ultrasonography, although it is occasionally used to differentiate a small pleural effusion from pleural thickening [13]. Since it can identify blood flow, some experts have proposed that color Doppler may reduce the risk of vascular injury from device insertion into the pleural space [14]. Further details are provided separately. (See "Ultrasound-guided thoracentesis", section on 'Site selection'.)
Image storage — Many portable ultrasonography machines have digital image storage and transfer capability that meets the requirements for image documentation. Alternatively, the machine may be equipped with a printer, thus allowing the clinician to place a hard copy of the study directly in the patient chart.
IDENTIFICATION OF PLEURAL EFFUSION USING ULTRASONOGRAPHY — The defining ultrasonography findings of pleural effusion are typical anatomic boundaries that surround a relatively hypoechoic space in which there are associated dynamic findings. (See 'The anatomic boundaries' below and 'The hypoechoic space' below and 'Dynamic findings' below.)
Imaging technique
Patient position — Since free-flowing pleural fluid moves to the most dependent position within the thorax, the preferred position is the seated upright position. However, not all patients are capable of sitting upright, in which case the supine or semi-supine positions are alternatives.
●Stable patients capable of sitting upright – Most patients who have adequate cardiopulmonary function are scanned in the upright seated position while resting their elbows on a secure surface that is placed in front of them. In this position, the entire back is available for scanning. The patient may also raise their arms to permit access to image the lateral and anterior portions of the chest.
●Unstable patients or patients unable to sit upright (picture 3) – Patients with severe cardiopulmonary failure (eg, critically ill patients) or bedridden patients who are unable to sit upright are scanned in the supine or semi-supine position with the ipsilateral arm adducted across the chest towards the opposite side. If the effusion is large, it may be identified in the mid-axillary line. If the effusion is small, it may be identified by moving the probe to a more posterior position, so that it is pressed into the mattress and angled upwards to visualize the effusion. Although this is helpful for identifying the presence of the effusion, it may yield an impractical angle for needle insertion when performing thoracentesis. Alternatively, the patient may be placed in a full lateral decubitus position with the hemithorax that is contralateral to the effusion in dependent position; or placed in supine position moving the patient towards the edge of the bed such that part of the posterolateral hemothorax is accessible for imaging. Positioning the critically ill patient for thoracentesis is often challenging and requires several team members to be involved. If the patient is on mechanical ventilatory support, one team member is assigned responsibility for maintaining position of the endotracheal tube throughout the procedure.
Machine setup — The ultrasonography machine is positioned so the screen is easily visible from the operator's working position and ambient lighting is reduced to maximize screen contrast [3]. The clinician adjusts the depth and gain settings on the machine for optimal visualization of the pleural effusion. Many portable machines have abdominal "preset" settings that work well for thoracic scanning (pleura and lung). Some machines have lung "preset" settings; these often do not yield good image quality in the author's experience. Depth is adjusted to place the target of interest in central screen position: shallow for examination of a near field structure such as the pleural surface, and deep for examination of the full extent of a pleural effusion. The gain setting is adjusted to optimize visualization of anatomic boundaries. (See 'The anatomic boundaries' below.)
The probe is held perpendicular to the skin surface and placed in between the rib space with the probe marker directed in cranial direction (movie 1); the scanning plane is adjusted to center the interspace on the screen with the ribs on either side of the image [10]. The probe marker standardizes image acquisition such that when it is in a cranial direction, this yields a longitudinal axis view of the interspace with the cranial direction projected to the left of the screen (with abdominal preset). Structures near the skin surface project to the top of the screen while deeper structures project towards the bottom of the screen.
Caliper function is a standard machine function that allows the operator to measure distance from the chest wall to the target area off of a frozen ultrasonography image.
Scanning technique — Because ultrasonography waves do not pass through air, acoustic gel is liberally applied to the patient's skin in the area of interest to provide an airless interface; gel also permits the ultrasonography probe to slide easily over the skin. The probe is systematically moved craniocaudally from one interspace to another and from right to left so multiple interspaces may be examined in a short time. A methodical scanning strategy allows a comprehensive analysis of the target effusion or other pleural pathology (picture 1). This process allows the examiner to:
●Locate relevant anatomic landmarks (eg, diaphragm, lung, heart) (see 'The anatomic boundaries' below)
●Identify and characterize any abnormalities (including pleural fluid), if present (see 'The hypoechoic space' below and 'Dynamic findings' below)
●Identify a safe site for needle insertion, if thoracentesis or biopsy is planned (movie 1) (see "Ultrasound-guided thoracentesis", section on 'Site selection')
If thoracentesis is performed separately from the initial diagnostic ultrasonography, the examination is always performed immediately before performance of the thoracentesis; as there may have been interim change in the size and distribution of effusion between and the two scans.
The anatomic boundaries — The diaphragm, chest wall, and lung are identified. The pericardium may also be a border, so it is prudent to identify the heart when planning thoracentesis on the left side (movie 2 and picture 4).
Diaphragm — Since subdiaphragmatic device insertion may cause catastrophic injury to the liver or spleen, the diaphragm is positively identified before any pleural procedure [3]. The diaphragm appears as an echogenic curvilinear structure above the liver or spleen (image 1); downward (caudad) movement of the diaphragm is normally seen with inspiration. The diaphragm is best confirmed by first identifying the splenorenal and hepatorenal recesses (the liver or spleen are cranial, and the kidney is caudal, to the respective recess). Although these recesses are curvilinear structures that may be confused with the diaphragm, they are differentiated by the identification of the associated organs (spleen, liver, and kidney) (image 2).
The position of the diaphragm is variable and may be unexpectedly low in the seated patient with a large pleural effusion. In contrast, it may be unexpectedly high in the supine patient or when there is coexisting abdominal obesity, ascites, or diaphragmatic paralysis.
Chest wall — Identification of the structures comprising the chest wall allows accurate measurement of the depth of needle penetration required for entry into the pleural space through the epidermis, dermal, and intercostal muscle compartments. The ultrasonography anatomy of the chest wall is as follows (picture 4):
●Epidermis – When using the high frequency linear probe (7.5 MHz), this is visible as an echogenic line in the near field that is a few millimeters in thickness. It is not visible as a distinct anatomic entity when using the low frequency (3.5 MHz) phased array probe. (See 'Transducers' above.)
●Dermis – This is visible as a hypoechoic area located deep to the epidermis.
●Intercostal muscles – These are visible as a hypoechoic area deep to the dermal compartment. The operator observes that the intercostal muscles contract with respiration. This is a prominent finding when the patient has respiratory distress.
●Ribs – These are visible as hyperechoic curvilinear structures adjacent to the intercostal muscle that represent the periosteum of the rib. The periosteum is associated with a posterior acoustic shadow that blocks visualization of structures deep to the rib. If the probe is over the medial anterior chest, rib shadowing is less prominent since the ribs are cartilaginous in this area, thereby permitting transmission of the ultrasonography beam.
●The pleural line – This is visible as a white line approximately 0.5 cm deep to the periosteal reflection of the rib. When a pleural effusion is present, the visceral and parietal pleura surfaces are separated by the pleural effusion. Measurement of the distance between the skin surface and the parietal pleura is made with the caliper function off of a frozen image. This distance constitutes the depth of needle penetration required to access the pleural effusion. (See 'Machine setup' above and "Ultrasound-guided thoracentesis", section on 'Angle and depth of needle insertion'.)
Lung (atelectasis/consolidation) — The surface of the lung constitutes the third typical boundary that is sought by the operator in identifying the presence of pleural fluid. This allows the operator to determine whether there is a safe trajectory for needle insertion into the pleural effusion without risk of visceral pleural laceration.
The lung appears as a tissue density structure demarcated by the effusion (with alveolar consolidation due to compressive atelectasis caused by the effusion) (image 3). The degree of atelectasis depends on the size of the pleural effusion with large pleural effusions resulting in lobar or even total lung compressive atelectasis and smaller ones resulting in minimal atelectasis.
The hypoechoic space — The pleural effusion appears as a relatively hypoechoic space (image 1 and movie 3) that is surrounded by the anatomic borders described above (see 'The anatomic boundaries' above). The pleural effusion may be characterized according to its pattern of echogenicity:
●Anechoic when it is echo-free (ie, black) (image 1 and movie 3)
●Homogenously echogenic when it is hypoechoic (ie, not anechoic) and no discrete echogenic are elements observed within the effusion (movie 4)
●Complex non-septated when discrete echogenic elements are observed within the effusion (movie 5 and movie 4)
●Complex septated when strands or septa are observed within the effusion (movie 6)
The pattern of echogenicity has clinical utility; the anechoic effusion is usually a transudate while the presence of echogenicity within the pleural effusion usually indicates an exudate. Pleural effusions with septations or internal echogenicity are generally exudates (movie 4 and movie 5 and movie 6 and movie 7). Pleural thickening greater than 3 mm, pleural nodularity, or coexisting lung abnormality detected with lung ultrasonography such as consolidation of abscess are all associated with exudative pleural effusion [15,16]. A swirling pattern, defined as floating mobile echogenic particles within the effusion is associated with exudative pleural effusion (movie 7) [17]. A retrospective analysis of 66 patients suggested that ultrasonography was more sensitive than chest radiography (69 versus 61 percent) but less sensitive than computed tomography (69 versus 76 percent) for the diagnosis of a complicated parapneumonic effusion [18].
Dynamic findings — A variety of dynamic findings are associated with a pleural effusion. These include movement of the diaphragm and heart as well as respirophasic and cardiophasic movement of the atelectatic lung, strands, septations, and echogenic material within the effusion.
Limitations — Patient-specific factors such as obesity, massive edema, heavy musculature, chest wall dressings, and inability to position the critically ill patient may substantially degrade image quality. Complex long-standing empyema collections may make it difficult to identify the characteristic ultrasonography features of a pleural effusion. If ultrasonography is not adequate for imaging, chest computed tomography is indicated. (See "Imaging of pleural effusions in adults".)
Guidance of thoracentesis — Ultrasound is typically used to guide thoracentesis, the details of which are provided separately. (See "Ultrasound-guided thoracentesis".)
EVALUATION FOR PNEUMOTHORAX — Portable ultrasound is used to detect the presence of a pneumothorax in several situations [19-25]:
●Evaluation for suspected procedure-related pneumothorax such as that following thoracentesis, central venous access, transthoracic biopsy, or transbronchial biopsy. When ultrasound is used to guide the procedure, the operator checks for pneumothorax using ultrasonography both before and following the procedure. (See "Ultrasound-guided thoracentesis" and "Central venous catheters: Overview of complications and prevention in adults" and "Flexible bronchoscopy in adults: Associated diagnostic and therapeutic procedures".)
●Evaluation of a patient with chest trauma for rapid evaluation for pneumothorax. (See "Initial evaluation and management of chest wall trauma in adults" and "Initial evaluation and management of blunt thoracic trauma in adults".)
●Evaluation for resolution of a pneumothorax following chest tube placement [23]. (See "Pneumothorax in adults: Epidemiology and etiology".)
●Evaluation of the patient with acute respiratory failure including those on mechanical ventilation. (See "Indications for bedside ultrasonography in the critically ill adult patient", section on 'Evaluation for pneumothorax'.)
Scanning technique and patient position — Air within a pneumothorax space is usually located in the least dependent position in the thorax. For this reason, the patient is best scanned in the supine or semi-supine position. The probe is held perpendicular to the skin surface with the scanning plane adjusted to examine through the rib interspaces over the anterior chest. The depth is adjusted so that the pleural line is located towards the middle of the machine screen. This improves visualization of the pleural line, as does reducing the machine gain. The phased array 3.5 MHz probe gives serviceable images, while the linear probe (7.5 MHz) may be used for improved resolution (see 'Transducers' above). Multiple adjacent rib interspaces should be examined in a short period of time by moving the probe across multiple rib interspaces.
Rarely, a loculated pneumothorax may be present in a dependent position in the thorax. This may require examination in a different position and location on the chest wall.
Ultrasonography findings — The presence of lung sliding and/or lung pulse is a definitive finding that excludes pneumothorax. The absence of lung sliding suggests the possibility of pneumothorax, but it is not specific, so clinical correlation is always required. The presence of a lung point is diagnostic of pneumothorax, but may not always be present (algorithm 1).
Excluding a pneumothorax
Lung sliding and lung pulse — The identification of lung sliding or lung pulse excludes the presence of a pneumothorax. With the transducer in a longitudinal orientation, perpendicular to the skin surface, and centered between two adjacent ribs, the pleural line is identified (see 'Chest wall' above). For patients who have a pleural effusion, the pleural line can be identified and lung sliding confirmed at the edge of the effusion:
●Lung sliding – Lung sliding is the term for when the respirophasic movement of the visceral against the parietal pleural surfaces is seen as a shimmering mobile pleural line that moves in synchrony with the respiratory cycle (movie 8 and movie 9).
●Lung pulse – A related finding is lung pulse, where the pleural line moves in a cardiophasic fashion due to transmission of the cardiac pulsations (movie 10).
The identification of lung sliding or lung pulse excludes the presence of a pneumothorax only at the site of probe placement. This, multiple rib interspaces should be scanned in a short period time in order to reliably and rapidly exclude pneumothorax at multiple places throughout the lung.
B lines and lung consolidation — The visualization of B lines, lung consolidation, or an effusion exclude pneumothorax independent of the presence of lung sliding and/or lung pulse. B lines result from alveolar-interstitial abnormality at the visceral pleural surface (movie 11). Their presence therefore indicates that the lung is fully expanded at the site of probe placement. Similarly, visualization of consolidated lung or an effusion excludes pneumothorax, for the reason that any amount of intrapleural air or fluid interposed between the parietal and visceral pleura will block all transmission of the ultrasonography beam. (See 'Lung (atelectasis/consolidation)' above.)
Confirming a pneumothorax
Absence of lung sliding and/or lung pulse — When pleural air is interposed between the visceral and parietal pleural surfaces, as occurs with pneumothorax, the air within the pneumothorax space acts as a complete barrier to the propagation of the ultrasound beam, so the movement of the underlying visceral pleura cannot be seen (movie 8). Lung sliding and lung pulse will be absent when there is a pneumothorax, as only the parietal pleural is visualized.
If lung sliding and/or lung pulse is absent this is suggestive but not diagnostic of pneumothorax, and it should be investigated by chest radiography. Loss of lung sliding may occur with processes that ablate the movement between the visceral and parietal pleura such as pleural symphysis from neoplastic, post-inflammatory, or therapeutic pleurodesis. Pulmonary bullae may cause absence of lung sliding. Significant muscle contraction and blockage of a mainstem bronchus (eg, bronchial intubation with blockage of the contralateral mainstem bronchus by the inflated endotracheal tube cuff or blockage by foreign body, blood clot, mucus plug, or tumor) will also erase lung sliding on the side of the occlusion (movie 9).
Lung point — Most pneumothoraces cause only partial collapse of the lung with some remaining areas of apposition of the visceral and parietal pleura, usually within the lateral or posterior chest cavity, depending on the size of the pneumothorax. The lung point is observed at the boundary between the pneumothorax (where there is no apposition of the pleura, so no lung sliding is seen) and the partially deflated lung (where there is still apposition of the two pleural surfaces so lung sliding is seen). It is visualized as the intermittent respirophasic appearance of lung sliding from the edge of the screen (movie 12). Lung point is 100 percent specific and 66 percent sensitive for detection of pneumothorax, but is not always present [4]. The high frequency 7.5 MHz probe is useful in identifying the lung point on account of its better resolution compared with the 3.5 MHz probe. (See 'Transducers' above.)
Limitations for identification of pneumothorax — Patient-specific factors such as obesity, edema, or heavy musculature may degrade image quality, so that the pleural line may not be visible.
The presence of subcutaneous emphysema can block visualization of the pleural line [19].
Vigorous intercostal muscle contraction adjacent to the pleura, as may occur in the patient with respiratory distress, may result in movement of the adjacent parietal pleural surface (movie 13 and movie 9). The inexperienced operator may mistake this for lung sliding. The movement of the pleural line by intercostal muscle contraction is different from the shimmering movement of lung sliding.
Ultrasonography for guidance of thoracostomy tube placement — Ultrasound can be used to place chest tubes for drainage of air and confirm resolution of a pneumothorax. These details are provided separately. (See "Thoracostomy tubes and catheters: Placement techniques and complications", section on 'Role of ultrasound or other imaging'.)
IDENTIFICATION OF MALIGNANT PLEURAL DISEASE — Malignant pleural disease can be identified with pleural ultrasonography examination but pleural ultrasonography is not diagnostic; definitive diagnosis requires tissue sampling. Machine setup, patient position, and imaging technique are identical as for assessment for pleural effusion. (See 'Imaging technique' above.)
If the patient has a pleural effusion, malignant disease is visualized within the effusion as single or multiple nodules of varying sizes that are adherent to the diaphragm, the lung, or chest wall (movie 14). The masses may be homogeneously or heterogeneously hypo- or hyper-echoic [3,11,26,27]. Disruption of the pleural line or lack of lung sliding suggests the possibility of transpleural extension [11].
In the absence of a pleural effusion, pleural malignancy may be visualized as masses or pleural thickening interposed between the inside of the chest wall and the adjacent aerated lung. Malignant pleural mesothelioma presents with multiple scattered pleural masses or a more diffuse mass encasing the lung.
The presence of nodules and/or pleural thickening >1 cm may be helpful in determining the likelihood of malignancy. In a study of 52 patients with suspected malignant pleural effusion, pleural ultrasonography correctly identified 26 of 33 malignant effusions and all benign effusions by using these criteria [26].
Detailed discussion of imaging pleural plaques, thickening, and tumors is provided separately. (See "Imaging of pleural plaques, thickening, and tumors".)
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" and "Society guideline links: Use of point-of-care echocardiography and ultrasonography as a monitor for therapeutic intervention in critically ill patients".)
SUMMARY AND RECOMMENDATIONS
●Point-of-care ultrasound – Point-of-care pleural ultrasonography is performed at the bedside by clinicians trained in its performance and interpretation using inexpensive portable equipment. Given the cost savings, time efficiency, convenience, accuracy, and clinical applications, it is often chosen by pulmonologists trained in its use as the preferred imaging modality for rapid bedside imaging of the pleura. (See 'Choosing bedside versus consultative ultrasound' above.)
●Equipment – A two dimensional ultrasonography machine with a 3.5 MHz phased array transducer is typically used for pleural ultrasonography (picture 1 and movie 1). This may be supplemented by use of a 7.5 MHz linear vascular probe for detailed visualization of the pleural line. Many portable ultrasonography machines have digital image storage and transfer capability or are equipped with a printer, so that the requirements for image documentation are met. (See 'Equipment' above.)
●Pleural effusion findings – The three defining characteristic ultrasonography findings of a pleural effusion include identification of the typical anatomic boundaries (diaphragm, chest wall, and lung (image 1)) that surround a relatively hypoechoic space (image 1 and movie 15) in which there are associated dynamic findings (eg, respirophasic or cardiophasic movement of lung, effusion, and diaphragm). (See 'Identification of pleural effusion using ultrasonography' above.)
●Pneumothorax findings – The presence of lung sliding and/or lung pulse is a definitive finding that excludes pneumothorax (movie 16). The absence of lung sliding suggests the possibility of pneumothorax but it is not specific (movie 17), so clinical correlation with chest radiography is required. The presence of a lung point is diagnostic of pneumothorax (movie 18), but may not always be present. The visualization of B lines, lung consolidation, or an effusion also excludes pneumothorax independent of the presence of lung sliding and/or lung pulse (algorithm 1). (See 'Evaluation for pneumothorax' above.)
●Malignant disease findings – Ultrasonography examination can identify malignant pleural disease as pleural masses, nodules, or thickening >1 cm (movie 19). Definitive diagnosis, however, requires tissue sampling. (See "Imaging of pleural plaques, thickening, and tumors" and 'Identification of malignant pleural disease' above.)
ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Peter Doelken, MD, FCCP, who contributed to earlier versions of this topic review.
آیا می خواهید مدیلیب را به صفحه اصلی خود اضافه کنید؟
