Image: Aseev artem Aims • To understand the basic principles and practical appl

Image: Aseev artem Aims • To understand the basic principles and practical application of transthoracic ultrasound • To be familiar with the sonographic appearance of the normal thorax • To identify basic thoracic pathology • To utilise ultrasound as guidance for transthoracic interventions A practical guide to transthoracic ultrasound Summary Transthoracic ultrasonography is a well-established, yet underutilised imaging modality in respiratory medicine. It allows for real-time and mobile assessment of thoracic disorders and can potentially augment the physical examination of the chest. Moreover, ultrasonography-assisted interventions can be performed by a single clinician without sedation and with minimal monitoring, even outside of the operating theatre. Other advantages of chest ultrasonography include the lack of radiation and the short examination time. Many indications for the use of ultrasonography beyond the visualisation of the pleura and related conditions (including effusions, thickening and pneumothorax) have been validated in the last few decades. These include the assessment of diaphragmatic dysfunction, pul- monary consolidation, interstitial syndromes, pulmonary embolism, and pulmonary and mediastinal tumours, provided they abut the pleura. Transthoracic ultrasonography is an ideal guide for thoracocentesis. Ultrasonography-assisted fine-needle aspiration and/or cutting-needle biopsy of extrathoracic lymph nodes, and lesions arising from the chest wall, pleura, peripheral lung and mediastinum are safe and have a high yield in the of hands of chest physicians. Ultrasonography may also guide aspiration and biopsy of diffuse pulmonary infiltrates, consolidations and lung abscesses, provided the chest wall is abutted. This review will focus on the basic indications and applications for transthoracic ultrasonography. Transthoracic ultrasonography can be performed with a basic, two-dimensional black-and-white ultrasound system; more sophisticated mod- alities, like M-mode or colour-flow Doppler, are very rarely indicated. A low-frequency probe (2– 5 MHz) with a curvilinear shape is suitable for screening of superficial and deeper structures, where as a high-frequency probe (5–10 MHz) with a linear shape is used for refined assess- ment. Higher frequency allows for superior resolution closer to the probe, but at the cost of reduced penetration [1–3]. A clinician should be familiar with the basic controls, including the ‘‘freeze’’, ‘‘depth’’ and ‘‘gain’’ functions [1–3]. The freeze function creates still images, on which measurements can be performed using the track ball. The depth function is a digital zoom that defines what portion of the scanned image is displayed on the monitor at a certain magnification. The scale is displayed on a vertical axis. High-frequency scanning is per- formed at a maximum depth of around 3–4 cm. Statement of Interest None declared. HERMES syllabus link: Module D.3.5 Breathe | December 2012 | Volume 9 | No 2 133 DOI: 10.1183/20734735.024112 Florian von Groote- Bidlingmaier, Coenraad F.N. Koegelenberg Stellenbosch University and Tygerberg Academic Hospital, Cape Town, South Africa F. von Groote-Bidlingmaier: Stellenbosch University, PO Box 19063, Tygerberg, Cape Town, 7505, South Africa florianv@sun.ac.za The depth should preferably be adjusted to allow the area of interest to fill the digital screen. The gain is, in essence, a measure for the amplification of the echoes and determines the brightness of the image, and should be adjusted to maximise the contrast between tissues. Optimal patient position for scanning is crucial to obtain the best possible images [1, 3]. Chest physicians often use available imagery (including chest radiographs or computed tomography scans) to identify the area of interest and determine the position of the patient [1, 2]. The posterior chest is ideally scanned with the patient sitting using a bedside table as an armrest, whereas the lateral and anterior chest wall should be examined with the patient in either the lateral decubitus or supine position. The pleura, peripheral lung tumours and consolidated lung can be visualised along the intercostal spaces [1]. Raising the arm above the patient’s head increases the intercostal space distance and aids in scanning in erect or recumbent positions. Folding the patient’s arms across their chest displaces the scapu- lae when scanning the upper posterior thorax. Visualisation of superior sulcus pathology can be achieved apically with the patient in the supine or sitting position. Liberal application of gel is the final step prior to scanning [1]. It is advisable to hold the probe like a pen with the outer part of the hand in contact with the skin and to reduce ambient lighting. The sonographer should maintain visual contact with the screen while the dominant hand moves the probe across the area of interest and the other hand is used to optimise the digital image by adjusting the depth and gain. Findings can be compared with the contralateral side, which can be used as a control. The normal thorax The skin, muscles and facia planes are visible with a low-frequency probe as a series of echogenic layers [1–3]. Ribs appear as convex structures on transverse (vertical) scanning, with posterior acoustic shadowing. When viewed longitudinally, the anterior cortex appears as an uninterrupted echogenic line. The visceral and parietal pleura usually appear as a single highly echogenic line no more than 2 mm wide representing the pleura and pleuropulmonary interface [1–3]. On a long- itudinal view, the pleural line will appear approximately 5 mm deep to the rib cortex [4]. The visceral and parietal pleura can be seen as two distinct echogenic lines on high-resolution scanning (fig. 1), with the latter seemingly thinner in appearance [1, 2]. The two layers glide over each other during inspiration and expiration, which gives rise to the ‘‘lung sliding’’ sign on real-time ultrasonography, which is best appreciated on longitudinal (vertical) scanning [1–5]. Its presence has a high negative predictive value for the diagnosis of a pneu- mothorax [4–7]. Aerated lung parenchyma cannot be visua- lised on transthoracic ultrasonography [1–3, 8]. The large change in acoustic impedance at the pleura–lung interface, however, results in horizontal artefacts, so called reverberation artefacts or A-lines, that are seen as a series of echogenic parallel lines equidistant from one another below the pleura [1–3, 7]. A few short, vertical ‘‘comet-tail’’ artefacts can be seen at the lung bases in normal individuals, and in all probability represent fluid-filled subpleural inter- lobular septa. B-lines are longer, pathological vertical artefacts that obliterate A-lines (see later) [5, 9]. Figure 1 The high-frequency ultrasound appearance of a normal chest. The chest wall (CW) consists of multiple layers of echogenicity representing muscles and fascia. The more prominent visceral (Pv) and parietal pleura (Pp) are seen as echogenic bright lines that slide during respiration. A reverberation artefact, also known as an A-line (A), is present within the lung (L), as well as a single comet tail artefact (C). Transthoracic ultrasound Breathe | December 2012 | Volume 9 | No 2 134 The diaphragm is best visualised through the liver or the spleen [1–3, 5]. It appears as an echogenic line, approximately 1–2 mm thick, which contracts with inspiration. Extrathoracic lymph nodes Ultrasonography provides visual access to cervical, supraclavicular and axillary lymph nodes, and it may aid in distinguishing malig- nant from reactive lymph nodes. Inflammatory lymph nodes have oval or triangular shapes and the fatty hilum appears echogenic on ultrasono- graphy, whereas malignant nodes are often bulky and show loss of the fatty hilum leading to a hypoechoic appearance [1–3]. Irregular borders can be a sign of extracapsular spread. Ultrasono- graphy has the added advantage that it can visualise supraclavicular or cervical lymph nodes in patients with superior vena cava obstruction, particularly when vascular congestion and swel- ling complicate physical palpation. Supraclavicular lymph nodes are accessible to ultrasonography-guided fine-needle aspira- tion (FNA), which has the advantage of providing a cytological diagnosis and patholo- gical staging (pN3) in one procedure. FNA of extrathoracic lymph nodes can even be per- formed outside of a dedicated operating theatre at the patient’s bedside [10]. Chest wall pathology High-frequency ultrasound can detect soft- tissue masses arising from the chest wall, including lipomas, abscesses and many other (mostly benign) lesions. Masses generally have variable echogenicity and ultrasonographic findings are too nonspecific to differentiate between the various aetiologies [1–3]. Ultrasono- graphy-assisted transthoracic FNA of these masses can readily be performed, as no aerated lung needs to be transversed during aspiration. Ultrasonography-assisted transthoracic FNA is generally performed under local anaesthesia, ideally with a 22-gauge injection-type or short spinal needle connected to a 10-mL syringe. The needle should contain a removable inner stylet to reduce contamination with chest wall tissue and blood [1, 3]. Rib fractures can also be visualised with ultrasound, which might even be more sensitive than radiography [11]. Bony metas- tases to the ribs can be detected by means of sonography and appear as hypoechoic masses that replace the normal echogenicity of the rib leading to a disruption of the cortical line [12]. Metastases are amenable to ultrasonography-assisted FNA. Both chest wall masses and thoracic bony metastases can be sampled by means of cutting-needle biopsy (CNB). These devices are more invasive and carry a higher risk of visceral or vascular trauma [3, 13]. Potential visceral trauma can be caused by inadver- tently passing the device through the ribs, as osteolytic rib metastases may provide less resistance than expected. Pleural pathology Pleural effusions Transthoracic ultrasonography is ideal uploads/s3/ guide-to-us.pdf

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