When E lines are not aligned, they are called “W lines” showing an image similar to the W letter. It is due to a random disposition of air bubbles in the soft tissue [31].

Pleural Pathology

Pleural Efusions

Chest ultrasound is a great tool for the study of pleural effusion and the detection of underlying diseases (Figs. 30.3a, b and 30.4a, b). It takes part of the pulmonologist guidelines for unilateral pleural effusion investigation [32]. The effusion is an echo-free zone between visceral and parietal pleural which displays changes of form during breathing. One can recognize dynamic fndings, such as the oscillation of the adjacent lung with respiration, cardiac pulsation and diaphragmatic movement, oating, and moving of echogenic particles or septations.

In large pleural effusion, the collapsed lung adopts a tongue-like shape and its oscillating movement is known as “lung apping” or “jellyfsh sign” [33] (Fig. 30.5). Ultrasounds are able to detect fve milliliters effusion in sitting position [34] and small amounts of liquid even located between the chest wall and diaphragm or close to a hypoechoic pleural thickening [35], but with the exception of uid captured in the interlobar space of aerated lung. In fact, sonography is more sensitive and specifc than conventional chest X-ray for pleural effusion identifcation in a standing position (100% against 71% and 99.7% against 98.5%, respectively [33].

Color Doppler mode differentiates small amounts of uid from pleural thickening. The “ uid color sign” is a color signal that appears with a uid collection in the pleural space during respiration or cardiac cycles and is absent in case of pleural thickening [34]. The “quad sign” and “sinusoid sign” are others signs valid for located pleural effusion detection with a specifcity of

97% [36–38]. The “quad sign” is a static sign on B mode, defned as a quadrangular image limited laterally by the acoustic shadows of the ribs, the “pleural line” and inferiorly by the regular surface of the lung which is always regular and roughly parallel to the pleural line [38]. The central anechoic image corresponds to a pleural collection.

The “sinusoid sign” is the equivalent of the “quad sign” on the motion mode. Based on the cyclic motion of the respiration, the lung within a pleural effusion gets closer to parietal pleura describing a sinusoidal pattern or “sinusoid sign” [38].

Four US pattern are recognized based on the internal echogenicity and characteristic of pleural effusion: anechoic pattern, homogeneously echogenic pattern, complex non-septated pattern (complex = with internal echoes), and complex septated pattern (septation = thick or thin and mobile) [10]. An echo-free uid collection is suggestive of transudate which contain no components whereas exudate appears as echogenic. In an exudative pleural collection, free echoes represent oating particles due to protein, cell-­ containing, and tissue debris, known as “swirling sign” or “plankton sign,” which is not pathogno-

monic. Post-in ammatory effusion can present “Honeycomb-like appearance” due to fbrin organization. In such cases, ultrasound avoids frustrating attempts of thoracentesis with the potential risk of injury. Empyema are seen highly echogenic with “snowstorm sign” or “whirlpool oating sign” inside suggesting tissue debris and air bubbles, and generally accompanied by pleural thickening depending on the stage of the disease. Malignant pleural effusion is usually anechoic with possible metastatic pleural nodules and thickening (Figs. 30.6, 30.7 and 30.8). Underlying tumoral processes can be detected through theuid. The effusion presents as well the “swirling sign” on B mode induced by echoes oating and making circular movement [39]. It may become septated in case of repeated diagnosis thoracentesis. Finally, hemothorax appearances vary regarding the time of the trauma: hypoechoic in fresh blood collection or echogenic occasionally with large layering structures representing clots [40]. In a clinical context of in ammation or infection, identifcation of septa in the pleural collection is suggestive of complicated pleural effusion and has clinical implications. Several studies have shown that patients with septated effusions needed longer chest tube drainage, longer hospi-

tal care and were more likely to require fbrinolytic therapy or surgery compared to those with non-septated effusions [41, 42].

Volume quantifcation with chest US is possible. Many studies demonstrate the correlation between the depth of pleural effusion and the volume of removed pleural liquid. More than 5 cm between the pleura and lung at the base predicted a drained volume > 500 mL with a sensitivity of

83%, specifcity of 90%, positive predictive value of 91%, and negative predictive value of 82% in patients receiving mechanical ventilation [43]. Balik et al. established the relationship between volume of pleural uid and maximum separation of pleural layers with a simplifed formula: V (mL) = 20 × Sep (mm). Signifcant correlation was found between separation and volume of pleural uid (r = 0.72; p < 0.001) [44]. Remerand

et al. use a multiplanar ultrasound approach increasing the accuracy of measuring pleural effusions in critically ill patients. Ultrasound evaluation was tightly correlated with drained volume (r = 0.84, p < 0.001) and with pleural effusion measure with CT scan (r = 0.90, p < 0.001). This new method seems to be more accurate than previous methods [45]. A practical way to classify the pleural effusion is: minimal or none if the echo-free space is confned to the costophrenic angle, small if pleural effusion occupied 1 or less than 1 rib space, moderate if it extended to 2 or 3 rib spaces and fnally large if it is more than 4 rib spaces. More than an exact measurement, what is desirable in clinical practice is an estimation of pleural effusion to correlate with a patient’s symptomatology, in order to indicate a possible therapeutic aspiration. The added table gives us an approximation of the uid volume [46]. Finally, quantifcation of the pleural effusion is useful for follow-ups.

Pleural Thickening

Pleural thickening is often defned as a focal lesion greater than 3 mm in width, arising from the visceral or parietal pleura with or without

irregular margin [6, 9, 10] (Fig. 30.9). Distinction between pleural thickening and small effusion is done on color Doppler mode (positive “ uid color sign” in pleural effusion with 89.2% of sensitivity and 100% of specifcity) [47] or on M-Mode (presence of “sinusoid sign” in pleural effusion) [36–38]. Diffuse pleural thickening is described in long-term exudative pleural effusion, asbestosis related effusion, empyema, and mesothelioma (see below). It is hypoechoic but often presents several echogenicities and accompanying pleural effusion. Calcifcation suggests chronicity and it is also present in empyema and tuberculosis [10].

Pleural plaques are descriptive in asbestos exposure, trauma, pneumonia, and chemical pleurodesis. They appear as a circumscribed, smooth border, hypoechoic lesion, and sometimes­ calcifed with adjacent non-calcifed pleural thickening [35].

Pleuritis should be diagnosed based on ultrasound findings and clinical correlation by an exclusion of other chest pain diseases. US shows a rough appearance and interruption of the normally smooth pleura (89.4%) with a small subpleural consolidation from 0.2 to 2 cm (63.8%) and localized parietal and basal pleural effusion (63.8%) [48]. Typical missing