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140 oracic ultrasound
“STEP SIGN”
PNX
LUNG
Figure 9 – Static representation of the lung point. The “step” between the lung pleura and the air
artifact determined by PNX is evident.
We believe that the use of the M-mode is not particularly useful. e use of high frequency
linear probes makes the diagnosis of PNX easy and rapid. In practical terms, its utility may
be limited only to the static iconographic documentation.
In pneumothorax, transverse reverberations can also be emphasized in depth. ey are
generated by the air, that replaces the lung with its characteristic echogenic undifferentiated
background. It is a phenomenon physically compatible with an absolute mirror.
Of course, pleural air tends to obscure any underlying visible parenchymal lesion. In case of
concomitant pleural effusion or hemothorax, the air floating on the liquid constitutes a kind
of diaphragm or curtain, that can eliminate the acoustic window generated by the fluid collection. In turn, the fluid may contain air bubbles in suspension generating specific artifacts25.
In a similar way, to the left, the cardiac acoustic window and the normal sliding of pulmonary
margins on the heart are deleted. ese physiological aspects are replaced by fixed air artifacts.
ey are often interrupted by cardiac systoles, that bring the heart in contact with the anterior chest wall, and allow its rapid and intermittent visualization (heart point) (Clips 6-7).
Clip 6 – Small anterior left PNX. The partial covering of the heart synchronous
with the cardiac systole is observed.
Clip 7 – Anterior left PNX. The heart is only partially viewable because of
the presence of pneumothorax.
Finally, as already anticipated, only non-massive PNX shows lung points. A complete lung
collapse may not show any lung point. Otherwise, lung points exist, but they are hidden in
the posterior costovertebral recess24 (Fig. 10) (Clips 8-10).
Pneumothorax 141
Figure 10 – In cases of non-complete collapse of the lung, the lung points typically identify the lateral
limit of the air collection.
Clips 8, 9, 10 – Sonographic scans of lung points.
It is important to keep in mind that ultrasound has some limitations in estimating the volume of PNX. Its extension is, on the contrary, well estimated based on where lung points are
placed. Finding the lung point beyond the anterior axillary line generally indicates important
PNX. It is not very rare that a fairly extended PNX is related to a modest volume (Fig. 11).
Clips 8, 9, 10 – Sonographic scans of lung points.
It is important to keep in mind that ultrasound has some limitations in estimating the vol-
ume of PNX. Its extension is, on the contrary, well estimated based on where lung points are
placed. Finding the lung point beyond the anterior axillary line generally indicates important
PNX. It is not very rare that a fairly extended PNX is related to a modest volume (Fig. 11).
Figure 11 – An ultrasound image can be identical both in the case A as in the case B. In A, the volume
of PNX is moderate, while in B it is minimal.
An operator studying a pneumothorax using ultrasound, must be certain that what he or she
sees is a real lung point, not localized pleural adhesions, able to mimic this sign. Some findings (mostly acquired with a relatively high frequency linear probe) may be helpful. e real
lung point has a clearly horizontal dynamics, i.e. it moves horizontally (although sometimes
imperceptibly) with breath. “Pleural” artifacts on the side of the aerial collection are obviously
absent (pure mirror artifacts). Finally, the air collection acquires a slightly higher position
142 oracic ultrasound
(toward the probe) compared to the pleura on the wall, that determines in the image a small
step (step sign).
Actually, it is sufficiently clear that ultrasound has a great diagnostic accuracy for the diagnosis
of pneumothorax. e first available data had already shown considerable values (80-95%),
but they were derived from non-homogeneous cases, in different fields and on different
patients (Table 3).
Table 3 – Studies published on the ultrasound diagnosis of pneumothorax in the Eighties and Nineties
Author Nr. pcs. Year Type of study Field
Wernecke [26] 8 1987 Subjects with Rx diagnosis of PNX Radiological
Walz [27] 2 1990 Blind, on traumatized subjects Surgical
Targhetta [28] 28 1990 Subjects with Rx diagnosis of PNX Pulmonary
Targhetta [29] 2 1992 Blind, after lung biopsy Pulmonary
Targhetta [25] 11 1992 HydroPNX, already diagnosed with Rx Pulmonary
Targhetta [22] 24 1993 Subjects with Rx diagnosis of PNX Pulmonary
Lichtenstein [30] 43 1995 Subjects already diagnosed with other means ICU
Sistrom [31] 13 1996 Blind, after needle biopsies Radiological
Most of these data have demonstrated the excellent performance of ultrasound (up to 95%
sensitivity, 91% specificity and 100% negative predictive power).
More recently, some studies were realized on groups of patients with sufficiently uniform
clinical conditions. ese are summarized in Table 4.
Table 4 – More recent studies on the ultrasound diagnosis of pneumothorax
Author Clinical records Type of study Results
Soldati et al.
(2000) [32]
Dulchavsky et al.
(2001) [33]
Rowan et al.
(2002) [34]
Knudtson et al.
(2004) [35]
72 hemithorax in 36 pts.
728 hemithorax in 364 pts.
54 hemithorax in 27 pts.
328 patients
Consecutive patients
Comparison with CT
Consecutive or randomly
selected patients
Consecutive or randomly
selected patients
Comparison with Rx
Prospective analysis
Comparison with Rx
Sensibility 94%
Specificity 100%
Sensibility 96%
Specificity 99%
Sensibility 100%
Specificity 97%
Specificity 99,7%
PPN 99,7%
Accuracy 99,4%
Since 2004 studies on PNX increased in number and quality, involving more than 1500
patients. e majority of these observations included trauma patients (50%), but also evaluated subjects in interventional echography (approximately 30%) or ICU (20%) settings. On
patients with trauma, diagnostic accuracy was very high (sensitivity 86-100%, specificity
97-99%); in other settings it was comparable (sensitivity 80-100%, specificity 94-100%)36.
Pneumothorax 143
Very recently, a study by Wilkerson and his coworkers37 has analyzed works on the sonographic
diagnosis of PNX. ey have concluded that ultrasound is excellent for this diagnosis (radiographic sensitivity 28-75%, ultrasound sensitivity 92-98%). ese data were considered
by the sessions of the International Consensus Conference on Pleural and Lung Ultrasound
(Winfocus), which ended in October 2010. e agreement between the panel experts was
perfect or very good about the following statements38:
• e signs to be used for ultrasound diagnosis of PNX are the absence of pleural sliding,
the presence of lung points, the absence of B Lines and of lung pulse.
• e technique that should be used on the patient in the supine position is to explore the
less sloping areas of the chest and then proceed laterally.
• Chest ultrasound should be used in all contexts where PNX enters into the differential
diagnosis.
• When compared with chest radiography performed on supine patients, chest ultrasound
shows a higher sensitivity.
Search for sliding in the deep
sulcus area
Sliding -
Search for artifacts
B Lines - B Lines +
Search for lung points
Lung point/s + Lung point/s -
The diagnosis of PNX is plausible but uncertain. If there
PNX
Figure 12 – Flow-chart for the diagnosis of PNX.
is PNX, it can be a PNX with massive lung collapse. If
PNX is suspected on the left, the heart region has to be
analyzed in order to look for “heart point/s”
Sliding+
Anterior PNX is excluded.
Search in typical areas (lateral,
apical, posterior), rare
144 oracic ultrasound
What is still missing, is a clear definition of the diagnostic accuracy of ultrasound in the diagnosis of “spontaneous” PNX. Probably, what has been shown in the trauma setting has similar
outcomes in other fields. In the absence of trauma, moreover, the presence of subcutaneous
emphysema rarely prevents the evaluation of the lung
39,40
.
Finally, the relative simplicity of this examination, even in extreme conditions, allows a diagnosis
in different scenarios, starting with triage and before transferring the patient to the health facilities.
e flow-chart shown in Figure 12 (on page 143) shows the steps for the diagnosis of PNX.
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18. Reissig A, Copetti R, Kroegel C. Current role of ultrasound of the chest. Crit Care Med 2011; 39: 839-845.
19. Volpicelli G. Sonographic diagnosis of pneumothorax. Intensive Care Med 2011; 37: 224-232.
20. Ding W, Shen Y, Yang J et al. Diagnosis of pneumothorax by radiography and ultrasonography: a meta-
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21. Nagarrsheth K, Kurek S. Ultrasound detection of pneumothorax compared with chest X-ray and computed tomography scan. Am Surg 2011; 77: 480-484.
Pneumothorax 145
22. Targhetta R, Burgeois JM, Chavagneux R et al. Ultrasonic signs of pneumothorax: preliminary work. J
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23. Soldati G, Testa A, Pignataro G et al. e ultrasonographic deep sulcus sign in traumatic pneumothorax.
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24. Lichtenstein D, Mezière G, Biderman P et al. e lung point: an ultrasound sign specific to pneumothorax. Intensive Care Med 2000; 26: 1434-1440.
25. Targhetta R, Bourgeois JM, Chavagneux R et al. Ultrasonographic approach to diagnosing hydropneumothorax. Chest 1992; 101: 931.
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146 oracic ultrasound
e results of these studies indicate that ultrasonography is more accurate than chest radiography for detection of
pneumothorax, supporting previous investigations.
Kwan RO, Miraflor E, Yeung L, Strumwasser A, Victorino GP. Bedside thoracic ultrasonography of the
fourth intercostal space reliably determines safe removal of tube thoracostomy after trauma injury. J Trauma
Acute Care Surg 2012; 73:1568-1573.
is limited ultrasound exploration can safely and efficiently determine clinical resolution of traumatic pneumothorax and aid in the timely removal of thoracostomy tubes.
Oveland NP, Lossius HM, Wemmelund K, Stokkeland PJ, Knudsen L, Sloth E. Using thoracic ultrasonography to accurately assess pneumothorax progression during positive pressure ventilation: a comparison
with CT scanning. Chest 2013; 143:415-422.
is study confirms the role of utrasound to estimate the pneumothorax extent. In a experimental porcine model
a linear relation between the pneumothorax size and the lateral position of the lung point was demonstrated.
7
Parenchymal lung patology
As already stated, lung air content strongly influences the acoustic behavior of the organ. A real lung ultrasound image exists only if its air
content is below a “threshold” level and if it is dispersed (discretized) in
very small aliquots. For producing a real image, the shape of the air should
not mask the solid echostructure that arises from the high prevalence of
tissue with respect to air. When the air/tissue ratio increases compared to
the solid echotexture, air artifacts become prevalent. Finally, when the air
dispersion, around a physiologic density of 0.2 g/ml, is strongly dominant, ultrasound interaction is represented as a near specular reflection.
➣ Echography of lung parenchymal diseases: general data
For interpreting lung pathology, in radiology two kinds of opacity are distinguished: those
interstitium-related (or interstitial pattern) and those located in the distal airspaces (airspaces
or alveolar pattern). In ultrasound, the first induces artifactual changes (production of B Lines
and white lung); the second causes airspace consolidations creating acoustic windows. When
an acoustic window is generated inside a healthy lung, a not anatomical field is erased and the
lung becomes as a sonographic solid organ (hepatization).
Traditional radiographic imaging is relevant for interpreting lung ultrasound and includes
radiographic density, nodular and micronodular production, more or less fine septal syndromes, and ground glass in Computed Tomograpy (CT)1. In this discussion, the radiologic
terminology will be maintained for its simplicity, for the anatomical basis from which it
originates and for its diagnostic importance.
Recently, a new vision of “interstitial syndrome” has emerged and it appears perfectly consistent
with the radiologic interpretation of interstitial lung disease. In echography, as in radiology,
the interstitial syndrome is present in an anatomically subverted, but still aerated lung as in a
healthy but less aerated lung. It is particularly true in a lung with a non-physiological loss of air2.
Since its first description in 19973, the interstitial syndrome has been attributed to a pathological enlargement of the interstitium that produces artifacts (B- Lines) where the septa
abutting the pleura are expanded. is was a dominant view in the literature. It was however
an anatomical conception, which assumed the precise identification of the source of the
artifacts, i.e. to identify them on the pleural line in relation to a certain structure (the interlobular septum), to count them, or to establish consistent and classifying distances between
them. is interpretation is present in various works, but never examined in depth and it is
probably very partial.
147
148 oracic ultrasound
In our interpretation
4-6
, B Lines with their different expressions (in terms of concentration
and coalescence), and white lung, show different ways of the ultrasound to interact with the
pleural plane and the subpleural air. e ultrasound message is a sort of “measure” of the
density and geometry of the pleural plane. In essence, B Lines and white lung outline the
non-consolidating hyperdense range of the subpleural lung. B lines reveal a peculiar inhomogeneity in acoustic interaction, from normal “mirror” to consolidation. is progression is
continuous and, as density is just a weight/volume ratio, it is actuated because of an increase
in the weight of the tissue (interstitium), or of a decrease in the aerial part (isobaric) or of a
combination of the two mechanisms. is means that a denser lung for exclusive loss of air,
but with normal interstitium, may show up on ultrasound with interstitial pattern.
Beyond experimental contexts, this is clearly evident in the lung compressed in an effusion,
whose pre-consolidating (or pre-hepatizing) phases have precisely the aspect of an interstitial
disease, or it is evident in strongly hypoaerated (but basically healthy) segments of the lung.
Naturally, all the stages of transition from an interstitial to an airspace (or alevolar) pattern
are anatomically detectable. It is however also likely that in the ultrasound investigation the
interstitial aspect prevails, because, being artifactual, it can cover contiguous and underlying
images of consolidation.
Pulmonary interstitial pathologies, which generate particular ultrasound images, are pulmonary edema (cardiogenic, inflammatory or lesional) and diffuse interstitial lung diseases.
Pneumonia, ARDS, contusions, atelectasis and pulmonary infarcts represent consolidating
diseases (anatomically alveolar syndromes or airspace pathology).
Productive pulmonary lesions (neoplastic and granulomatous diseases) are classified aside.
ey do not have a peculiar acoustic behavior in ultrasound, but are characteristic for the
context in which they occur and the location they may have.
e conditions mentioned above as interstitial7 and airspaces8 diseases always involve the
pulmonary cortex. Cardiogenic pulmonary edema is a cortical disease. Peripheral involvement
of the cardiogenic pulmonary edema is secondary to the plasmatic idrostatic ultrafiltration,
which takes place primarily in the large lung interstitium. ARDS is also a cortical disease of
the lung, as demonstrated by studies employing radioactive ligands for inflammatory cells and
mediators9. Moreover, the target of inflammation in ARDS are the alveolar-capillary membranes and their highest concentration is at the cortical level. Finally, the pleural emergence of
lobar pneumonia is obvious. Bronchopneumonia have a bronchial and bronchiolar origin, but
inflammation and dysventilatory events inevitably reach the segmental periphery of the organ.
is clashes with the neoplastic disease, which in most cases has a bronchogenic and central
origin. e neoplasm grows infiltrating the neighboring tissue, but, unless it causes atelectasis,
it can remain for a long time or always settled in a tissue. is tissue may be normal on the
surface. is is the main reason why neoplasms and large not emerging granulomas cannot
fully benefit from lung ultrasound.
➣ Interstitial pattern
Interstitial syndrome
is term includes a well-defined anatomical situation of the lung, typical aspects in radiological imaging and a seemingly simple pattern in echography, consisting of the arrangements of
the so-called B Lines. erefore, it is essential to understand what a B Line is.
Parenchymal lung patology 149
e original description3 referred to an artifact visually similar to the ring-down, first called
“comet tail artifact”. Its description was purely qualitative: “hyperechoic reverberation artifact,
with narrow origin, which expands like a laser beam to the bottom of the screen”.
ese artifacts had a sensitivity of 93.4% and a specificity of 93% toward subjects with “diffuse alveolar-interstitial syndrome” proved, in most cases, with chest X-ray (which is not a
gold standard). CT was used as a comparison only on 29 subjects (11.6%)3.
Anyway, the excellent sensitivity and specificity of these signs pointed one of the most useful
applications of this method. Its role became evident in differentiating dyspnoea due to cardiogenic cause (acute pulmonary edema, sensitivity 100%, specificity 92%) and pneumogenic
dyspnoea (chronic obstructive pulmonary disease)10. In this perspective, pulmonary edema
became the prototype of the disease characterized by comet tails, then called B Lines.
Even today, this distinction between “bronchial” syndromes and edema is a strength of lung
ultrasound.
It is clear that B Lines intercept cases of acute pulmonary edema and, as we shall see, other
interstitial diseases, with practically absolute sensitivity
11-13
. Curiously, for more than a decade
B Lines have been defined in purely qualitative terms, i.e. those of the initial study mentioned.
erefore, we find it important to reiterate the concept that if B Lines have an undoubted
usefulness especially in emergency, in reality they are only “errors” of ultrasound machines
that interpret in their own way acoustic interactions. In reality, we do not currently know
the mechanism of formation of these artifacts, what is the best frequency or probe to detect
them, or even the best machine to make them appear unequivocally.
e definition of B Lines has remained the same over the years, since at present we do not
know what they are and whether they should be expressed only as images.
Even from a methodological point of view B Lines were evaluated in several studies with different probes and frequencies. In this way, what appears with a sector probe is not the same
thing as with a linear probe, capable of affecting perpendicularly the pleural plane with higher
frequencies. e linear probe, in fact, shows more artifacts and, above all, different types of
vertical artifacts. It provides a more accurate definition of their confluence and of “the white
lung”. It clearly differentiates long (full screen) and short (1 cm or less) artifacts and, finally,
it determines their punctiform or micronodular origin.
For a general examination of wet (with B Lines) or dry (COPD or pulmonary embolism)
lung, this fine analysis may not be necessary14. However, for distinguishing different interstitial
syndromes (e.g. cardiogenic edema, ARDS or pulmonary fibrosis), a detailed study of the
pleural plane and the underlying artifacts could be very useful15.
Pulmonary edema
e diagnosis of cardiogenic pulmonary edema, and its distinction from other situations that
cause dyspnea as chronic obstructive pulmonary disease (COPD), was the first application
of ultrasound in lung pathology.
e normal subpleural plane of the lung shows no detectable particular, outside the pleural
line, the so-called A and Z Lines and a moderately echogenic background. is is probably
attributable to the backscattering and to the differential amplification of the machine. When
higher frequencies are employed, in addition to the exaltation of the pleural line, a rapid attenuation of the acoustic energy, that is largely reflected, is observed.
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