**4.1. Pleural effusion**

For the purpose of investigation pleural fluid can be divided into three broad categories according to etiology: infective, malignant and miscellaneous. The infective etiologies result in either a para-pneumonic effusion or an empyema. Malignant effusions are due to primary or secondary thoracic disease, which may be pulmonary or pleural. The miscellaneous causes of pleural fluid include sterile benign effusions, haemothoraces and chylothoraces. Pleural effusions are differentiated into transudates or exudates on the basis of biochemical analysis of the aspirated fluid. The erect chest radiograph is the most common first line radiological investigation. Whereas approximately 500 ml of pleural fluid is required before an effusion can be identified clinically, as little 200 ml will blunt the costophrenic angle. US in either a standing or sitting position [1] not only is able to detect smaller volumes of pleural fluid than the erect frontal chest radiograph but it also gives useful information about the nature of the effusion. The pleural effusion images in ultrasound appearances are characterized by an echofree space between the visceral and parietal pleura. The formulae to estimate the volume of pleural effusions are well documented [1-5], but the different variation of actual volume was found in individual condition. The classifications of the volume of pleural effusion known currently are minimal, small, moderate, and massive. The minimal effusion indicate the echofree space is seen within the costophrenic angle; small effusion indicates the space is greater than costphrenic angle but still within a one-probe range; moderate effusion indicates the space is greater than one-probe range but within a two-probe; and massive effusion indicates the space is bigger than two-probe range.

### **4.2. Pleural effusion echogenicity**

**Figure 1.** During chest US examinations, patients can be in the seated or supine position (Figure 1.1 on the left; Figure

Because air cannot be visualized by US, the normal lung parenchyma cannot be detected by US theoretically. The image of chest US in chest wall including muscle, fascia, bone, and pleura (Figure 2). The soft tissue echogenicity with multiple layers means muscles and fascia. The normal ribs appear hyperechoic surfaces with prominent acoustic shadows beneath the ribs. Approximal 0.5 cm below the ribs shadows, the visceral and parietal pleura appear as an enchogenic bright line. During respiratory movement, the two pleural lines glide with each other which is referred to as the "Gliding sign". Therefore, the "Gliding sign" means normal parietal and visceral pleura slide over each other during respiration and the loss of "Gliding

For the purpose of investigation pleural fluid can be divided into three broad categories according to etiology: infective, malignant and miscellaneous. The infective etiologies result in either a para-pneumonic effusion or an empyema. Malignant effusions are due to primary or secondary thoracic disease, which may be pulmonary or pleural. The miscellaneous causes of pleural fluid include sterile benign effusions, haemothoraces and chylothoraces. Pleural effusions are differentiated into transudates or exudates on the basis of biochemical analysis of the aspirated fluid. The erect chest radiograph is the most common first line radiological investigation. Whereas approximately 500 ml of pleural fluid is required before an effusion can be identified clinically, as little 200 ml will blunt the costophrenic angle. US in either a standing or sitting position [1] not only is able to detect smaller volumes of pleural fluid than the erect frontal chest radiograph but it also gives useful information about the nature of the effusion. The pleural effusion images in ultrasound appearances are characterized by an echo-

**3. Chest wall: Muscle layers, bone, and pleura**

84 Advancements and Breakthroughs in Ultrasound Imaging

sign" can be seen in pneumothorax or diffuse pleural thickening.

1.2 on the right).

**4. Pleural disease**

**4.1. Pleural effusion**

The strength of ultrasound lies in demonstrating characteristics of the pleural fluid itself. Four basic ultrasounds patterns of internal echogenicity of pleural effusion were identified and they can be subclassified as anechoic, complex nonseptated, complex septated, and homogenously echogenic (Figure 3). Anechoic effusion is defined as echo-free spaces between visceral and parietal pleura. Complex nonseptated effusion is defined as heterogenous echogenic materials inside the pleural effusions. Complex septataed effusion is defined as fibrin strands or septa floating inside the pleural effusions. Homogenously enchogenic effusion is defined as echogenic spots density evenly distributed within the effusion [2, 3]. A purely anechoic collection is found in exudates and transudates with equal frequency. However, internal echoes in the form of septations or focal areas of debris are due invariably to exudates. US presentations in transudative pleural effusions are not always in an anechoic pattern. Tran‐ sudative pleural effusions may have a complex nonseptated pattern or an anechoic pattern [4].

**Figure 2.** Sonographic images of normal pleura and chest wall using a 5-MHz convex scanner. (A) Transverse image through the intercostal space. The chest wall is visualized as multiple layers of echogenicity representing muscles and fascia. The visceral and parietal pleura appear as echogenic bright lines that glide during respiration (gliding sign). Re‐ verberation echo artifacts beneath the pleural lines imply an underlying air-filled lung. (B) Longitudinal image across the ribs. Normal ribs are seen as hyperechoic chambered surfaces (arrowheads) with prominent acoustic shadows be‐ neath the ribs. Pp, parietal pleura; Pv, visceral pleura; L, lung

There was no transudative pleural effusion with complex septated or homogenously echogenic pattern [5]. The ability of chest US to detect underlying disease was comparable to that of computed tomography (CT) in pleural and parenchymal lesions [6]. The applications of sonographic appearances in effusions of febrile patients in the intensive care unit (ICU) can determine the necessity of thoracentesis in high risk patients with effusion in ICU [7]. This study reported that complex nonseptated and relatively hyperechoic, complex septated and homogenously echogenic pleural effusion patterns might predict the possibility of empyema in febrile patients in the ICU. The sonographic septation in lymphocyte-rich exudative pleural effusions can help us differentiate tuberculosis pleurisy from malignant pleural effusion [8].

**Figure 4.** Lung sliding (on M-Mode sonography). P, pleura. Panel (A) shows the granular 'sea-shore' appearance of normal lung sliding. Panel (B) shows the horizontal 'bar-code' appearance that occurs with loss of lung sliding

Ultrasound Diagnosis of Chest Diseaseses http://dx.doi.org/10.5772/55419 87

The normal aerated lung is difficult to image because the dramatic change in acoustic impe‐ dance between chest wall and lung results in specular reflection of ultrasound waves at the pleura. However, consolidated lung has a tissue density and echo-texture similar to liver, analogous to pathological hepatisation. This removes the change in acoustic impedance at the pleural interface, and ultrasound waves pass directly into the affected lung. When patient with lobar or segmental pneumonia and the lesion is adjacent to pleura or in the pleural effusion, the pneumonia may be detected by chest US. A marked consolidation with air-bronchogram and treelike ramifications is easily seen (Figure 7). Within the consolidated area, hyperechoic (white) foci may be visible, again representing a change in acoustic impedance, but this time at the tissue interface between solid lung and air-filled bronchi. Subpleural nodule also can be

**Figure 5.** Pneumothorax. Chest US reveals stratosphere sign

**5.1. Pulmonary lesions**

seen in chest US (Figure 8).

**Figure 3.** Sonographic appearance of pleural effusion (PE). The effusion can be subclassified as anechoic (A), complex nonseptated with spots(arrows) floating inside effusion. D, diaphragm (B), complex septated (arrows) (C), and homo‐ genously echogenic (D)
