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80 oracic ultrasound
Costophrenic sinus
Lung
(curtain)
Figure 13 – Image illustrating the anatomical relationships of the zone of apposition of the diaphragm,
bounded on the left by pulmonary curtain (maximum inhalation, diaphragmatic thickness 4.7 mm).
Wall
Diaphragm
Liver
Finally, when evaluating a chest with echography, we believe it is useful to estimate in an
“eyeball” way the position of the coronal hemidiaphragms to the right and to the left.
A high hemidiaphragm position may indicate paresis or paralysis. A lower positions of the
hemidiaphragms, substantiated by patterns of well aerated lung fields (mirror or hypermirror)
may justify a diagnosis of pulmonary hyperinflation or emphysema.
➣ Position of hemidiaphragms and the diaphragmatic zone of
apposition
Dimensions (thickness) of the diaphragmatic zone of apposition and its kinetics (inspiratory
thickening) were defined above. is region also has an interest for the estimation of the
diaphragmatic shortening, the position of the hemidiaphragms and the descent of the lung
in the costophrenic sinus. To overcome the qualitative estimation (eyeball) of position of the
hemidiaphragms17, it is necessary to quantify the dynamics of the diaphragm against the wall.
During the interpretation of a chest X-ray, the position of the hemidiaphragms indicates
whether the lungs are hypoexpanded, restricted, or hyperexpanded as in emphysema and
obstructive lung diseases. In X-ray of normal subjects, the right diaphragmatic dome is projected at level of the 10th thoracic vertebra, the left one at level of the 10th to 11th vertebra
In obese patients, they have a higher position.
e hemidiaphragms descend laterally into the costophrenic sini through a muscular portion that is adherent to the chest wall. Diaphragmatic muscle is anchored to the sternum,
to the last six ribs and to the medial and lateral arcuate ligaments20. Ultrasound is useful for
the quantification of certain parameters related to the diaphragmatic respiratory mechanics,
referring to the size of the thoracic zone of apposition of this muscle21.
Very schematically, the diaphragm, in its entirety, has a tendinous center (dome) and a
cylindrical portion directly juxtaposed to the chest wall (zone of apposition). is can be
measured as area, or as length along any thoracic line. e apposition area constitutes a substantial and variable portion of the total area of the rib cage: when we consider the residual
18,19
.
Semiotics of chest ultrasound 81
volume it can be estimated as more than half of the total area, while when we consider the
total lung capacity it tends to zero22. When the patient is standing, breathing at rest, it is
one quarter to one third of the total area of the rib cage. However the length assessment of
the zone of apposition of left and right hemidiaphragms is much more practical, when we
consider a line between the middle and anterior axilla23. As already seen, this assessment is
easy in echography (Figs. 12 and 13).
A linear probe placed longitudinally, just anterior to the midaxillary line, allows to identify
the costal origin of the diaphragm, when the patient is breathing shallowly.
When patient takes a deep breath, it is possible to observe a muscle layer (3-5 mm thick, on
average, 3.2 +/- 0.8 mm) deviating from the wall for a variable distance and getting thicker.
is length is dynamic when breathing and tending to zero when the lung tends to total lung
capacity, and it correlates with the diaphragm length.
With this technique it was observed that the length of the diaphragmatic zone of apposition
during a deep inhalation varies between 7 +/- 6 mm. is value correlates with the total lung
capacity. e length is 71 +/- 9 mm at the functional residual capacity (FRC), and 110 +/- 12
mm at residual lung volume (RV)23.
Patients with severe COPD show a length of the diaphragmatic zone of apposition reduced
by 20% compared to healthy controls.
Table 1 lists some data on normal respiratory mechanics, that can be acquired through echographic exploration of the diaphragmatic regions.
Table 1 – Parameters related to normal respiratory mechanics of diaphragm
Anatomical diaphragmatic excursion 1-2 to 7-11 cm
Diaphragmatic excursion in echography
(M-Mode, hemicoronal)
Diaphragmatic excursion in echography
(M-Mode, intercostal)
Thickness of the diaphragmatic zone of
apposition
Length of diaphragmatic zone of
apposition (mid-axillary line)
Excursion of lung bases
Maximum inspiratory lowering of 4.9 cm to the right
and 5 cm to the left
1.8 +/- 0.76 to 7.9 +/- 1.3 cm, forced inspiration
3.2 +/- 0.8 to over 4 mm
0.7 +/- 0.6 cm at total lung capacity, 7.1 +/- 0.9 cm at
RFC, 11 +/- 1.2 cm at RV
9.2 +/- 3.1 cm between maximum inspiration and
expiration
➣ The study of the diaphragm during mechanical ventilation
Physiological and pathophysiological correlations of the diaphragm with ventilatory function,
lung volumes and respiratory work are well known.
At present there are no studies concerning the evaluation of diaphragmatic dynamics during
mechanical ventilation. We believe that this is a promising field of development.
According to our observations, echography can be an extraordinary means to provide evidence
of complex pathophysiological situations.
82 oracic ultrasound
Figure 14 shows diaphragmatic excursions in a patient ventilated in the conventional way.
Figure 15 shows diaphragmatic excursions of the same patient ventilated with NAVA (neurally
adjusted ventilatory assist). It is evident that diaphragmatic excursions increase with NAVA
ventilation, while the respiratory rate drastically decreases.
EXPIRATION
Figure 14 – M-Mode visualization of diaphragmatic excursion during conventional mechanical
ventilation.
EXPIRATION
INSPIRATION
INSPIRATION
Figure 15 – The NAVA-mode provides evidence of an increased diaphragmatic excursion and a
decreased respiratory rate.
Semiotics of chest ultrasound 83
Figures 16, 17, 18 show the case of a mechanically ventilated patient (CPAP + PS) for respiratory failure related to COPD exacerbation. e reduction of pressure support (PS) results in
a net increase in diaphragmatic excursion. e excessive ventilatory support in this case was
deleterious, as it was determining a net reduction in patient’s neuromuscular activity. Clips
6-7 provide evidence of the improvement of the diaphragmatic kinetics in B-Mode.
Figure 16 – M-Mode evidence of diaphragmatic excursions with PEEP 10 cm H2O and PS over PEEP
18 cm H2O.
Figure 17 – PS reduction to 10 cm H2O results in an increased diaphragmatic excursion.
84 oracic ultrasound
Figure 18 – Further reduction of PS to 6 cm H2O results in a further incremented diaphragmatic
excursion.
Clip 6 – Diaphragmatic excursion with PEEP 10 cm H2O and PS 18 cm H2O
over PEEP.
Clip 7 – Diaphragmatic excursion with PEEP 10 cm H2O and PS 6 cm H2O
over PEEP. The greater amplitude of the diaphragmatic excursion is evident.
➣ Echographic semiotics of the chest: definitions
e following are some definitions that characterize the pleuropulmonary echographic
semiotics25.
ey are important in the fields of lung pathology and traumatology and they essentially represent the stereotyped expression of the disease in ultrasound imaging (Tab. 2 end of chapter).
ese findings will be described in the various chapters relating to specific pathological
conditions.
However, we find it useful to make some preliminary remarks about some of the sonographic
findings of the lung. ese findings are based on a terminology that is now accepted (Volpicelli
G, Elbarbary M, Blaivas M et al.; International Liaison Committee on Lung Ultrasound (ILCLUS) for the International Consensus Conference on Lung Ultrasound (ICC-LUS). International
evidence-based recommendations for point-of-care lung ultrasound. Intensive Care Med 2012;
38(4): 577-91), but is certainly susceptible to future changes based on the improvement of
knowledge on the acoustic interactions of the cortical lung.
Semiotics of chest ultrasound 85
One of the most controversial topics refers to ultrasound artifacts. A Lines and B Lines are
widely used and are accepted definitions (E Lines and Z Lines much less)9, however they
refer to images which are inevitably and strongly influenced by the frequency and mode of
insonation of the pleural plane. It is predictable, and understandable, that their expression
and morphology change, in terms of quantity and quality, depending on the instruments
(probes and machines) used, they can therefore follow an evolution over time due to changing
technologies. Moreover, it is sufficiently clear that their expression is a complex and continuous phenomenon, not characterizable as dichotomous (A and B).
In simple terms, A Lines can be bright, light, many, few, short, long, thick, thin etc. B Lines
may appear the same way. It is evident that the meanings could be different
26,27
.
Although not yet fully understood, this ‘simplified’ semiotics will still be used in the following pages. On the contrary, other terms, though equally valid, such as comets, comet tails,
ultrasound lung comets, ring down, artifacts of repetition etc., won’t be used.
Pleural line
e pleural line is an important landmark in lung ultrasound for the topographic orientation
of the operator. It lies deep down the rib shadows and appears as an echogenic line. e echo
of the pleural line measures less than 2 mm when measured with convex probe and an average
of 1 mm when measured with linear probe. However it is useless to measure its thickness for
clinical purposes, since the pleural echo has a strong component of reflection and is therefore
largely artifactual. In spite (or as a consequence) of this, the exploration of its surface (real
image) is better when relatively high frequencies are used, and it is also possible with the use
of very low mechanical indexes (0.4-0.9).
Figure 19 – To the left, a perfectly linear pleura. To the right, an irregular pleura. In this case a straight
segment, placed tangentially to the pleura, makes its irregularities manifest (arrows).
e pleural line is normally linear. e linearity of the pleura in ultrasound is of great importance, because pleural irregularities are one of the expressions of lung pathology (diffuse
interstitial lung disease, ALI/ARDS, pleurisy). It is intuitive that the irregularity appears as
a pathological pleural surface (grainy, micronodular, cobblestone-like etc.) and this irregular appearance is evident when a pathological pleural region is bordered by a normal one.
Nevertheless an objective definition, or a grading, of the pleural irregularity have never been
proposed. In our experience, the tangent method allows to obtain the objectivity of the pleural
86 oracic ultrasound
irregularity. In essence a straight line is placed (actually or ideally) along the pleural plane,
producing the alignment of the more echogenic points on the pleural line, or its surface if
it is evident. If micro- or macronodularity of variable thickness between 0.5 and 1 mm, appear above this line, we speak of first-grade pleural irregularities. If micro- or macronodules
overcome the tangent for more than 1 mm, we speak of second-grade pleural irregularities
(Fig. 19).
Pleural sliding
e lung movement during the respiratory activity is physiologically caused by the expansion
of the thoracic cavity, which, in turn, originates from the contraction of the diaphragm and
of the external intercostal muscles. rough this movement the pleural pressure surrounding
the lung varies, and the air flows into the airways. Consequently, the lung expands passively
and the visceral pleura flows along the chest wall, moving with a minimum friction due to
the lubricating effect of the fluid normally present in small quantities in the pleural cavity
(about 10 ml).
e pleural line physiologically slides (sliding sign) moving in synchrony with the excursions
of the lungs while breathing (Clips 1-2). erefore, it articulates the pulmonary dynamics and
the sliding sign disappears in case of apnea, pleural adhesions, pneumothorax, and atelectasis
28,29
e sliding is less evident at the lung apices, which are physiologically less mobile (Clip 3). e
lung bases show the maximum lung movement, equal on both sides (Clips 4-5). In normal
subjects, studied with dynamic three-dimensional MR, the intraparenchymal movement of the
lung bases in the range between maximal inspiration and expiration was 9.2 +/- 3.1 cm30. is
movement in normal subjects is closely related to the expansion of the diaphragmatic zone of
apposition, in turn caused by shortening (contraction) of the muscle. At apex level the movement is 2-3 cm and it progressively increases from the apices to the bases. e sliding is still
evident in the case of emphysema or parenchymal bubbles, although in these cases it must be
carefully searched using a linear probe.
A patient in apnea doesn’t show pleural sliding, however his pleural line is moved by a biphasic
movement synchronized with the cardiac systoles and it is obviously more evident on the left,
because of the proximity of the heart. We called this sign “physiological lung pulse” to distinguish
it from the one related to complete pulmonary atelectasis28 (Clip 8).
.
Clip 8 – Evidence of normal pleural sliding and of the physiological
paracardiac lung pulse. In the right part of the clip, the heart is visible.
e lung pulse may be seen with tissue Doppler (TDI) focused on the visceral pleura. is
way, the sliding appears as a wide low-frequency movement, while the pulse is a short biphasic
acceleration of the pleural line with the same frequency of the heart.
In our opinion, the pleural sliding is better visible when using a linear probe and operating
with relatively high frequencies (around 6 MHz) in the fundamental mode. For this purpose
it is useful to also decrease the gain appropriately. is makes the pleural line evident on a
dark background.
e pleural sliding is an integral part of the lung curtain in the costophrenic sinus and it also
appears as a curtain at the edge of the heart, covering it with deep breaths. e exploration of
the pleural sliding (or pulse) to the borders of the heart window is very important to exclude
Semiotics of chest ultrasound 87
small pneumothorax (where reverberations of intrapleural air are fixed) of the left anterior
pre-and paracardiac region.
Lung points31
ey represent the points on the pleural line where the regular pattern of the sliding (indicating the wall contact) is suddenly replaced by a static pleural pseudoline. In fact, the stillness
of an air reflection adjacent to a physiologically mobile pleural line is the landmark of free
intrapleural air. Lung points show the outline of a pneumothorax, so even a single, unequivocal lung point is pathognomonic of pneumothorax32. e absence of lung points, however,
does not exclude pneumothorax. On the contrary, it is typical of massive pneumothorax,
with total lung collapse.
In supin patients, lung points placed in front of the midaxillary line, show relatively small air
collections, while lung points medial to the mammillary lines show minimal pneumothorax,
often invisible to X-rays in the supine position (occult pneumothorax)
4,32
(Fig. 20) (Clips 9-10).
Figure 20 – Anterior pneumothorax: to the right, normal lung with evidence of B Lines, to the left
pneumothorax area with no B Lines; the transition point between these two areas identifies the lung point.
Clip 9 – To the left, absence of pleural sliding, to the right normal lung (lung
point).
Clip 10 –
To the left, evidence of sliding sign, not present to the right (lung
point).
e so-called “pseudo lung point” should be distinguished from a true lung point. It sometimes appears at the edge of a subpleural emphysema bubble. Especially in case of lungs with
interstitial disease, the operator can see a normally moving pleura in a certain point, but
88 oracic ultrasound
he could also highlight an apparently static echogenic reflection contiguously to that point
(bubble hypermirror), producing the false image of a lung point (Clip 11). is diagnostic
difficulty does not exist, when using a high frequency probe, that can enhance the details and
the movement of the pleural line.
In the case of a small retro-parietal air collections, two lung points33 can be represented in
the same scan. One of the two lung points indicates the outer side of an air collection and
the other one its medial limit. It is a sign of extremely small pneumothorax (Clip 12). e
opposite is more rare, i.e. two lung points due to a lung area surrounded by air which marks
its margins (Clip 13).
Clip 11 – Two lung points not due to pneumothorax, but relative to bullous
emphysema and pulmonary fibrosis. B-lines exclude the presence of air in
the pleural cavity.
Clip 12 – Two lung points in a minimum anterior pneumothorax.
Clip 13 – Opposite situation to the previous case. The two lung points delimit
the area of the lung along the wall.
Normal “lung”
e normal lung is the field below the pleural line, characterized by transverse reverberations
defined A Lines. In ultrasound, the normal lung has no anatomical representation. At this level
there is no evidence of tissues, septa, bronchi or vessels, because of the kind of image obtained.
A Lines are typical reverberations of the transducer, that are generated because the normal
pleural plane is a strong reflector inside the chest wall. ey are horizontal reflections placed
at the same distance. is distance is equivalent to the distance between the transducer and
the anatomical pleura
9,25,28
.
Other echogenic planes of the chest wall are evident as mirror effect when the chest wall is
thin and little attenuating, and when in the subpleural background there is a limited noise,
that does not obscure the reflections. For this reason, the mirror effect does not occur if the
subpleural background is particularly echogenic because of interstitial disease.
Sometimes, on typical subpleural background, fixed vertical echogenic enhancements appear
and they do not cover the A Lines. ese findings, which should not be confused with B
Lines, are of uncertain origin and have been defined Z Lines9 (Figs. 21-22).
In cases of high reflection of the pleural plane (like on emphysema bubbles and when the
air content in the lungs is increased), the so-called Z lines are placed on the point where the
scan is strictly perpendicular. ey appear as echogenic horizontal lines densely overlapping.
is phenomenon has been called “hypermirror” for the possible genetic role of a normal
insonation over a massively reflective pleural plane (Figs. 23-24).
Semiotics of chest ultrasound 89
Z LINE
Figure 21 – A Z Line.
Figure 22 – a: Z Lines. They appear when a relatively high acoustic energy impacts on highly reflective
contiguous planes (generally of the chest wall). Reverberations between these plans generate repetitive
signals displayed on the screen. Their non-pleural origin explains the lack of movement when breathing,
their dependence on a normal insonation, and their disappearance with the movements of the probe. The
sonographic evidence is also linked to a strong reflectivity of the pleural plane, that is why they overlie A
Lines. b: A Lines are exactly equidistant from each other and they come from the reverberation between
the probe and the pleural plane.
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