Chest
Volume 122, Issue 5, November 2002, Pages 1759-1773
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Reviews
Real-Time Chest Ultrasonography: A Comprehensive Review for the Pulmonologist

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This review discusses real-time pulmonary ultrasonography (US) for the practicing pulmonologist. US supplements chest radiography and chest CT scanning. Major advantages include bedside availability, absence of radiation, and guided aspiration of fluid-filled areas and solid tumors. Pulmonary vessels and vascular supply of consolidations may be visualized without contrast. US may help to diagnose conditions such as pneumothorax, hemothorax, pleural or pericardial effusion, pneumonia, and pulmonary embolism in the critically ill patient who is in need of bedside diagnostic testing. The technique of US, which is cost-effective compared to CT scanning and MRI, may be learned relatively easily by the pulmonologist.

Section snippets

Technical Equipment

Visualization of the chest wall requires a higher frequency linear probe (5 to 7.5 MHz), whereas pleural and pulmonary pathology is better detected with a sector or phased array probe with lower frequency (3.5 MHz).3,4 A convex array probe (3.5 to 5 MHz) combines the advantage of adequate close resolution and the ability to access deeper structures between the ribs. All described examinations were performed by a pulmonologist. Recently developed, and still expensive, devices having

The Technique of US Examination

To examine anterior and posterior parts of the chest, the patient should be in a sitting position with arms elevated and hands clasped behind the neck (Fig 1). Even with this technique, some parts of the upper lobes remain hidden behind the scapulae. Pleural movement is observed during inspiration and expiration. Solid lesions close to the diaphragm require special maneuvers, such as sniffing or coughing. The probe may be moved in longitudinal and transverse directions to visualize the lung

Chest Wall

Numerous studies5,6,7 evaluating US chest wall imaging have been published. The visibility of muscle and bone has steadily increased with equipment advances (Table 1). Different parts of the chest wall may now be well-delineated with current techniques (Fig 1). The margins of normal ribs are outlined as uninterrupted echogenicities similar to normal pleura, while the pleura is moving continuously during respiration. The US beam passes through cartilage better than through muscular tissue.

Normal US Findings

Less than 1 mm of space is usually present between the parietal and visceral pleura. A thin echogenic lining represents parietal pleura. The visceral pleura may be slightly blurred due to reflection artifacts from the US beam as it encounters a lung surface. Both pleural surfaces may rarely be visualized on standard US pictures. However, the parietal pleura does not move, whereas the visceral pleura moves with respiration.

Pleural Effusion

US imaging is the best method for diagnosing pleural effusion and

Comparison of US With Other Imaging Methods

US is more sensitive than posterior-anterior and lateral chest radiographs in detecting small amounts of pleural fluid.31 Pleural fluid is even more difficult to discern on radiographs taken with the patient in the supine position.17,32 On decubital chest radiographs, the differentiation between atelectasis and effusion is occasionally difficult. US better estimates the volume of effusion than radiography.32 US is useful to evaluate pleural opacities by differentiating atelectasis, effusion,

Pulmonary Embolism

A variety of imaging techniques for patients with pulmonary embolism (PE) has been studied. The first step in the diagnosis is the chest radiograph. It shows infiltrates, atelectasis, and effusions.39 Ventilation-perfusion scintigraphy is the next step in many institutions. However, the investigators in the Prospective Investigation of Pulmonary Embolism Diagnosis study40 found that only a minority of patients with PE had high-probability scans (sensitivity, 41%; specificity, 97%). One hundred

Pneumonia

Peripheral pulmonary lesions that extend into the visceral pleura may be visualized by US. US differentiates atelectasis and effusion when opacities are present. Inflamed lung parenchyma shows hypoechoic consolidation with blurred margins. The echo-texture is homogeneous and occasionally mimics lung parenchyma, with multiple lentil-sized air inlets.59,60 Echo-texture varies with ventilation. It is heterogeneous with ventilation or homogeneous with small or absent air inlets. The air bronchogram

Transthoracic US of the Mediastinum

The most common disorders of the mediastinum in adults are metastasis and primary malignancy. Benign disorders, such as cysts, thymomas, or lipomas, are rare.88,89 The imaging technique designated for evaluating the mediastinum is chest radiography, followed by CT scanning. Although an adequate view of the mediastinum is somewhat impaired by bone, US plays a useful role. In 1971, Goldberg90 first described suprasternal US of the mediastinum. Cardiologists used this access to examine the aortic

US-Guided Biopsy

For many years, pulmonologists were limited to the use of fluoroscopy-guided transthoracic biopsies. The introduction of CT scanning in the 1980s allowed clinicians to increase the range of biopsies. Real-time US-guided biopsy of the chest wall or pleural lesions has been performed for years.106 Encouraging results for chest wall lesions,107,108 pleural lesions,109 pulmonary lesions,110,111 and mediastinal lesions112,113,114 have been reported. US-guided aspiration biopsy is successful with

US in the ICU

Bedside US offers many possibilities in the ICU setting. Critically ill patients receiving positive-pressure ventilation may develop life-threatening complications during transport or during positioning in the CT scanning or MRI suite. Rapid diagnosis is crucial in deteriorating patients and in acute emergencies. US is invaluable for the immediate detection of pericardial or pleural effusions. The differential diagnosis of pleural fluid may be easily achieved133 (eg, hemothorax simulating liver

Summary

New imaging techniques have considerably improved the diagnostic and therapeutic capabilities of the pulmonologist.139 US has a valuable role, yet, it is operator-dependent, and training is required. It is a supplement for areas requiring more detailed views. Bedside availability and the absence of radiation allow more patients to be suitable candidates. A diagnosis of liquid or solid masses is easily achieved, and thoracentesis is performed with a low risk of complications. Pulmonary lesions

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    This work was supported by the Division of Pulmonary Medicine, Center of Internal Medicine, Nuremberg, Germany.

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