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Using ultrasonography in the diagnosis and management of pleural disease: how to interpret "floating lung" and comet tails.

Article Excerpt
ABSTRACT: The increasing availability of bedside ultrasonography allows for more timely diagnosis and treatment of pleural effusion while limiting the patient's exposure to radiation. The dynamic signs characteristic of pleural effusions include respirophasic changes in the shape of the fluid collection, floating movements of atelectatic lung, and the plankton sign. Ultrasonography also is an efficient means of excluding pneumothorax when rapid diagnosis is needed or after interventions such as central line placement, lung or pleural biopsy, or thoracentesis. The diagnosis of a pneumothorax relies on the absence of dynamic signs such as "lung sliding." Static signs, such as the comet tail artifact, or consolidated lung parenchyma or lung tissue that contains a solid mass, also can be useful in excluding pneumothorax. Ultrasonography can be used to guide fine-needle aspiration and core biopsies of pleural nodules, pleural thickening, and subpleural lung masses.

KEY WORDS: Ultrasonography, Pleural effusions, Pneumothorax

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Ultrasonography is an important modality in the evaluation of pleural disease. The increasing availability of portable ultrasonography units in clinical areas, such as procedure suites, emergency departments, and ICUs, has made ultrasound equipment accessible to many physicians involved in the treatment of patients with pleural pathology.

However, as sophisticated as modern hand-carried ultrasonography units are and as good as image quality has become, an understanding of the principles of ultrasonography and image interpretation has to be brought to the bedside by the physician. Fortunately, pleural ultrasonography poses few challenges to the beginning physician-sonographer. This makes it ideally suited, with vascular access sonography, for the enterprising novice, especially when compared with limited echocardiography or abdominal ultrasonography.

The primary challenges of pleural sonography are the identification of pleural effusion as well as the safe and successful performance of drainage procedures. Pleural ultrasonographic findings and uses are summarized in Table 1. A glossary of the relevant terms is presented in Table 2.

In this article, we will review the use of ultrasonography in the evaluation of pleural effusions and pneumothorax and the role of interven tional ultrasonography in patients with pleural disease.

THE BASICS

Ultrasound hardware

In recent years, high-resolution portable ultrasonography units have become ubiquitous in the hospital setting. In general, sonography machines that are capable of abdominal ultrasonography or echocardiography are also suitable for pleural sonography. Specifically, convex array or sector scanning ultrasound probes with frequencies between 3 and 5 MHz provide a good balance between near-field resolution and depth penetration. Transducers that have higher frequencies are more suitable for the evaluation of the chest wall. Color Doppler is of limited use in pleural ultrasonography.

There is no standardized operator interface for sonography machines except for an adjustable marker on the screen that corresponds...

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