Because the air in the pleural space tends to redistribute anteriorly in a decubitus position, the third to fourth intercostal space in the midclavicular line is generally the most appropriate starting point for assessment.

A major criterion for the diagnosis of pneumothorax is the absence of “lung sliding” in B mode (sensitivity of 95% and negative predictive value of 100%) [55].The “seashore sign” is the equivalent of lung sliding on the M mode, normally seen in healthy person (straight motionless aspect representing chest wall = “sea” above a granular layer = “shore”) which is indicative of the phasic movement of the lung. In the presence of pneumothorax, the “seashore sign” is typically absent and replaced by the “stratosphere sign” or “bar code sign” (only straight motionless layer).

Another typical ultrasound sign of pneumothorax is the “A line sign” which is represented by an exaggerated A lines artifact and the absence of vertical B lines. This association increases the specifcity and it rounds 96% for the diagnosis of complete pneumothorax. Keep in mind that the presence of a single B line is enough to rule out a pneumothorax [21].

In case of incomplete lung collapse (partial pneumothorax), the “lung point” is seen at the point where the lung edge reaches the chest wall. It is a 100% specifc sign for pneumothorax. Another ultrasonic sign is the “double lung point,” which represents the separation of visceral and parietal pleura in case of localized pneumothorax [56].Between these two points there is no lung sliding neither B-lines, but laterally to the points, normal pleural signs are evident [57–59].

Contrary to pleural effusion, sonography is not useful to quantify the volume of pneumothorax. It is a binary system to rule out (or not) the pneumothorax but not to precise its degree. Although, many authors consider the hypothesis that the more laterally the lung point locates, the larger size of pneumothorax would be [60, 61]. In the animal model, Oveland et al. demonstrated the linear relation between the pneumothorax size and the lateral position of the lung point [62]. However, the differentiation between small and large pneumothorax using the lung point by bed-

side ultrasound is still considered as a grade C in the 2012 international evidence-based recommendations [16].

The “lung pulse” is an ultimate sonographic sign useful in the diagnosis of pneumothorax and consists in the transmission of cardiac pulse to pleural line, given that the visceral and parietal pleura contact with each other. Volpicelli and colleagues give an important value to the lung pulse sign, when lung point cannot be detected, by stating that “even in the absence of lung sliding and B lines, visualization of a lung pulse rules out pneumothorax” [63].

Keep in mind that, the presence of lung sliding in all parts of the pleura rules out the pneumothorax with 100% cases [55]. However, the absence of lung sliding is not specifc to pneumothorax. Potential false positives may occur with ARDS, a history of pleurodesis, massive fbrosis, extensive pneumonia, and pleural adhesions, asbestos-­ related diffuse pleural thickening, giving to this sign an approximate specifcity of 91% [55]. False positive diagnosis of pneumothorax may also arise in severe acute asthma and emphysematous patients, particularly with anterior bullous disease, due to absent lung sliding. Slater et al. (2006) affrm that chronic obstructive pulmonary disease (COPD) patients can mimic the appearance of pneumothorax on US; therefore, they recommend confrmation with other imaging modalities [64].

Ultrasonography may be used routinely to screen for postprocedural pneumothorax after transthoracic interventions and may obviate the need for routine post-procedural chest radiographs. However, a disadvantage of ultrasound is the lack of quantifcation of a pneumothorax and the assessment of the indication for chest tube drainage [65].

Pulmonary Pathology

Pathological process in the lung parenchyma can be detected with ultrasonography when it’s located in the peripheral part of the lung with a pleural contact, or when aerated lung is replaced by consolidated lung tissue or fnally when a

pleural effusion exists which allows US beams transmission. “Consolidation” can be identifed by ultrasound including pneumonia, pulmonary embolism, lung tumors, atelectasis or pulmonary contusion [16].

A correct diagnosis should be always done by ultrasound based on clinical correlations.

1.Pneumonia: It is visible sonographically if the consolidated lung directly opposes the pleura, or if there is an adjacent pleural effusion which acts as an acoustic window. Pneumonic consolidation tends to appear as irregular echogenic area with serrated and somewhat blurred margins, isoechoic to the liver and containing multiple echogenic foci which correspond to air flled bronchi called “bronchoaerogram,” “bronchopneumogram” or “air bronchogram.” Air bronchogram is a branched linear hyperechoic image with millimetric lenticular shape echoes (Fig. 30.10). It represents a specifc sign for lung consolidation. “Dynamic air bronchogram” is another specifc sign and it is defned as an inspiratory centrifugal movement of bronchogram on B mode and highlighted on M mode. It has 94% specifcity and 97% positive predictive value for diagnosing pneumonia and distinguishing

Fig. 30.10  Sniff respiration

it from obstructive atelectasis [66]. The deepest part of the pneumonic process often has an irregular border descripted in the literature as the “shred sign” [67].

Sonography assessment may be of particular beneft in critical care, in order to avoid transportation of unstable patients [68] and in pediatric patients avoiding excessive radiation [69, 70].

Peripheral lung abscesses may also be detected by ultrasound. These appear as rounded, hypoechoic, or anechoic lesions surrounded by echodense tissue. Deep abscesses and those surrounded by air are not detectable by ultrasound.

In general, the size of pneumonia appears smaller on ultrasound than on radiographs because of the presence of artifacts, surrounding air of ventilated lung parenchyma and because of the narrow acoustic window.

Another detail regarding centimetric and peripheral pneumonia is the “C line.” C is coming from centimetric cupuliform consolidation. C line is a sonographic image of small lung consolidation. It represents somehow the shred sign for the small and very distal alveolar syndrome [71].

2.Passive atelectasis. Passive or compression lung atelectasis is due to a moderate or large pleural effusion compression. The typical sonographic image is a homogeneous and echogenic tongue-like lung with sharp and smooth borders. Limit border with ventilated parenchyma is blurred. There is a typical capacity of reexpansion during/after pleural volume evacuation. During inspiration, because of the increase of air in the atelectatic area, air bronchogram can appear.

3.Post-obstructive atelectasis. It is important to differentiate it from a pneumonic consolidation or passive lung atelectasis. Central tumor is the origin of the distal and obstructive atelectasis and it is identifed as a homogenous and hypoechoic area. In general, the amount of the pleural effusion is moderate or small, even absent in some cases. And contrary to passive atelectasis, there is an absence of reventilation with inspiration or with the evacuation of the pleural effusion. Depending on the duration of the obstruction, evidence of “ uid bronchogram” is typically present. This sign is visualized as a branching pattern of anechoic structures with hyperechoic walls, without perfusion signs inside on color Doppler differentiating it from vessels. Special attention should be paid in a persistentuid bronchogram during follow up. That should raise suspicion of poststenotic etiology and will require additional studies such as a CT scan and eventually bronchoscopy.

Another ultrasound characteristic is the absence of both “lung sliding” and “lung pulse” [72].

4.Neoplastic consolidation. Tumor process is identifed as a hypoechoic structure with infltrating borders known as “fnger-shaped ramifcations” [73]. It is mainly non-homogeneous with sometimes necrosis areas. Contrarily to in ammatory diseases, tumoral processes are not ventilated and are well demarcated from the surrounding lung tissue. Tumor consolidation may still contain residual ventilated areas with some bronchial branches. Lung metastasis can be seen when they reach the edge of the lung, in contact with the pleura.

Progression to the chest wall of peripheral tumor is possible to be detected by ultrasound (see extrathoracic pathology). Targeted investigation with a correct transducer allows the physician to make a correct extension diagnosis and staging of the tumor.

5.The white hemithorax. It’s a challenge for the physician to determine the exact cause between potential number etiology of unilateral lung opacity. The hemithorax can be potentially occupied by massive lung consolidations and complete obstructive or by large pleural effusion or a combination of these. Chest ultrasound plays a crucial role for the assessment and to determine what is the next step in the study of such disease (tap the pleura, pleural biopsies, chest drain insertion, bronchoscopy…). Using B mode and Doppler mode, the physician can be more confdent to differentiate a “conventional pneumonia” from a post-obstructive pneumonia which require a different therapeutic approach. The same thing is true for loculated pleural effusions, that will not resolve by a simple pleural tap [74].

6.Interstitial lung diseases. They are characterized by multiple comet tails artifacts distributed over the entire lung associated with pleural thickening, irregular and fragmented pleural line, and subpleural consolidation in some cases. Minimal amount of pleural uid can be present [75]. The typical ultrasound pattern in a longitudinal scan is constituted by 7 mm regularly spaced comet tails which correspond to thickened interlobar septae (7 mm corresponds roughly to the average size of a lobule), coming from the pleural line and spreading up without fading to the edge of the screen. It is known as the “septal rockets pattern” in opposition to the “ground-glass pattern” present in the alveolar edema, where B lines are regularly spaced in 3 mm and con u- ent to the pleural line [18, 76]. Presence of isolated B lines in a panel is not considered diagnostic of interstitial syndrome. Ultrasound interstitial syndrome examination is considered positive when three or more B lines are simultaneously visible between two ribs [76].

7.Pulmonary embolism or lung infarction.

Acute pulmonary infarcts are most frequently visualized as a hypoechogenic pleural-based wedge shaped area, usually in the lower lobes and often associated with a localized pleural effusion [77]. Other typically sonographic features include within the wedge-shaped area of parenchymal abnormality, the absence of arterial ow [78]. Lung infarction has been described as “consolidation with little perfusion” [79, 80]. The overlapping sonographic appearances of pulmonary embolism with other subpleural pathologies such as pneumonia, subpleural tumors, and pleurisy limit its use as a primary diagnostic tool. Small studies have shown ultrasound to have a specifcity ranging from 66 to 87% [77, 81, 82].

Evaluation oftheDiaphragm

The diaphragm is visualized sonographically as a three-layered structure: a central hypoechoic muscular layer bounded by two echogenic lines representing the diaphragmatic pleura and peritoneal membrane. It is best examined in the lower intercostal spaces through an organ window (liver and spleen). The diaphragm contracts during inspiration (moves downwards) and relaxes

during expiration (moves upwards). Both hemidiaphragm move together. In healthy subjects, 1–2.5 cm of excursion in quiet breathing and 3.6–9.2 cm during deep breathing are considered normal [83] (Figs. 30.11 and 30.12). Up to 9 cm can be seen in young or athletic individuals in deep inspiration. Excursion in women is slightly less than men [83].

Diaphragmatic paralysis is suggested by an absence of movement or paradoxical movement during respiration which can be accentuated with forced inspiration (“sniff test”) (Fig. 30.13). Paradoxical movement is easily detectable in case of large pleural effusion with an inverted shape form of the dome. In general, those patients will present severe dyspnea after a while until they present a diaphragmatic fatigue. Thoracentesis is mandatory to improve the symptomatology and to relieve muscle function. Remember that the puncture should be done at least at two intercostal rib spaces from the inverted dome. The restitution of the normal shape of the diaphragm during evacuation of theuid can occlude the trocar and consequently produces pain in the homolateral shoulder and neck (innervation of the central part of the diaphragm by cervical nerve C3 and C4). Whileuoroscopic evaluation of the diaphragm is the most commonly used technique to assess paraly-