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220 oracic ultrasound
Figure 59 – Pulmonary embolism. X-ray and lung ultrasound without significant anomalies (a and
b). Thrombosis of the popliteal vein (c), scintigraphic confirmation of pulmonary embolism with multiple
perfusion defects.
Figure 60 – Same patient as in Figure 59 three days after the diagnosis. Multiple subpleural
consolidations.
Clips 50, 51 – Small pulmonary infarcts in patients with pulmonary
embolism with few symptoms.
e combination of parenchymal lesions, small basal pleural effusion and “sentinel” pleural
fluid is very suggestive.
Ultrasound embolic consolidations must be differentiated from similar lesions attributed to
primary or secondary tumors, pneumonia, contusions or scars.
Parenchymal lung patology 221
For this purpose, the use of ultrasound contrast agents (LCEUS) may be useful. Last generation utrasound contrast that allow continuous acquisitions showing the microvasculature of
the consolidation are preferred. e intravenous administration of 2 ml of sulfur hexafluoride
(SonoVue) produces a fast enhancement of the consolidating lesion if it is due to atelectasis
or pneumonia. e echogenicity reached after 5-7 seconds is similar to that which the spleen
acquires after 20 seconds. is early enhancement is related to the prevailing pulmonary
vasculature of pneumonia and etelectasis. Embolized or infarct consolidations show no
enhancement or are characterized by a poor peripheral contrast acquisition through the
bronchial circulation (18-20 sec)
168
.
e diagnostic accuracy of ultrasound for detecting PE is based on a few studies. e original
ones, about thirty years ago, showed values above 90%. Later, Mathis and his co-workers
confirmed these optimistic results.
More recently, Pfeil and Reissig
169
in a study where the ultrasound was compared to contrast
enhanced CT obtained values of sensitivity and specificity of 70% and 69% respectively (82%
and 100% using CT). ese figures resize better diagnostic accuracies derived from past studies.
“Normal” subpleural pattern in pulmonary embolism
We believe that the evidence of subpleural abnormalities in pulmonary embolism depends on
the time elapsed from the event. is may explain our bad experience in detecting the images
described in patients undergoing ultrasound early after the onset of symptoms. Moreover,
even Mohn and coll.
170
report predictive values of 79%, not sufficient to exclude such an
important disease.
If pulmonary consolidation can be the anatomic expression of an obstructive vascular lesion
in the lung, we believe that normal findings should be emphasized in the context of a clinical
situation suggesting PE. is is especially true in the Emergency Room where the patient is
seen early compared to the symptoms.
erefore, a perfectly normal ultrasound imaging (a pattern with subpleural A Lines) in a
dyspnoic patient, especially shortly after the onset of symptoms, requires the search for a
possible PE.
A normal lung echographic pattern must trigger a work up indicating the execution of a
pulmonary CT angiography. However, the physician should not forget the evaluation of the
heart and of the deep veins of the lower limbs. is is an immediate, simple, fast and real
time test. Its duration is only a few minutes (3’-5’) for the experienced sonographer.
In submassive or massive pulmonary embolism, heart may show an overload of the right sections (see in the chapter on echocardiography). A patient with shock and an acute enlargement
of the right heart is virtually a patient with PE. A normotensive patient with an overload of
the right heart potentially has a high-risk pulmonary embolism. e same patient with deep
vein thrombosis (DVT) probably has PE, but is nonetheless indicated antithrombotic therapy
Finally, the positivity of CUS in a clinical setting suggesting pulmonary embolism makes
further diagnostic assessments unnecessary. is happens in about 10% of cases
157
.
According to this multidirectional strategy, called “kill three birds with a stone”, in ultrasound
the pleura and lung surfaces should be evaluated first. Subsequently the right cardiac chambers are the target. Finally, the question that must be answered is related to the presence or
absence of a DVT (the three birds).
e existence of a recent venous thrombosis greatly simplifies the management of these patients, because it suggests an anticoagulant treatment.
222 oracic ultrasound
Heart in pulmonary embolism
e echocardiographic involvement of the right ventricle characterizes massive (with hemodynamic instability) and submassive (without hemodynamic instability) pulmonary embolisms.
Both hemodynamic instability and signs of right ventricular dysfunction are predictors of
mortality.
e heart is evaluated with two-dimensional ultrasound according to apical, parasternal, long
and short axis scans
171-175
. Pulmonary embolism produces a variable degree of volume and
pressure overload on the right ventricle. Its clear expression, according to the parasternal short
axis projection, is the flattening or the protrusion of the septum towards the left ventricle.
e left ventricle is normally circular in this scan “O shaped”. In PE it assumes a “D” configuration, which indicates a systo-diastolic compression due to pressure overload through
the septum (Fig. 61).
RIGHT VENTRICLE
Figure 61 – Massive pulmonary embolism. Marked dilatation of the right ventricle and flattening of the
interventricular septum. The left ventricle loses its spherical shape for a “D”-like shape.
INTERVENTRICULAR SEPTUM
In addition, in normal subjects the systolic motion of the free wall of the right ventricle and
the lateral wall of the left ventricle is similar and symmetrical in the direction of the interventricular septum. In PE McConnell
175
described a right ventricular dysfunction (hypokinesia),
which is regionally localized in the free wall of the right ventricle sparing the apical region
(McConnell sign). Finally, in the apical four chambers scan, the normal size of the right
ventricle is inferior to the left ventricle. Whenever the transversal area of the right ventricle
exceeds that of the left ventricle, a right ventricular dilatation is confirmed.
e availability of a Doppler device can estimate the pulmonary systolic pressure through the
calculation of the right atrial pressure and of the speed of the jet from tricuspid regurgitation
(see chapter on echocardiography and hemodynamics).
Deep vein thrombosis (DVT) of the lower limbs
DVT is part of the spectrum of thromboembolic disease and is its main pathogenetic factor.
For a Chest, ICU or Emergency physician it is important to focus on venous thrombosis as
one of the most common causative factor of pulmonary embolism
176
.
Parenchymal lung patology 223
A rapid diagnosis of DVT facilitates the management of critically ill patient. DVT in a patient
with suggesting symptoms is highly predictive of pulmonary embolism. Moreover, DVT requires the same anticoagulant therapy of pulmonary embolism. erefore, ultrasound scanning
of the large veins of the lower extremities is very informative about current or future events.
DVT usually originates in the distal veins of the lower limbs (calf). Many thrombi confined
below the trifurcation of the popliteal vein, may resolve spontaneously and do not induce
symptoms
When thrombosis involves the iliac or femoral veins, symptoms are frequent
177
.
178
. Approximately
50% of untreated femoropopliteal venous thrombosis cause pulmonary embolism in the following three months. About 10% of patients with symptomatic DVT develops an important
postphlebitic syndrome the following five years
179-180
.
Inherited thrombophilia (factor V Leyden, prothrombin gene mutation, deficiencies of protein
C, protein S, or antithrombin) or acquired thrombophilia (antiphospholipid antibodies) are
a cause or a contributing cause for 40-60% of thromboembolisms in Caucasians
e diagnosis of DVT begins on the probability of disease (score of Wells or similar)
181
.
182-183
and
the patient’s symptoms. However, an accurate diagnosis cannot be separated from objective
tests because many conditions can simulate a DVT (venous insufficiency, complicated Baker’s
cyst, hematoma)
184-185
. e evaluation of D-dimer based on latex test has an unsatisfactory
sensitivity (80-85%) to conduct a screening on subjects without disease.
e dosage with the ELISA method is the most sensitive (> 90%). Its low specificity strongly
limits the usefulness of D-dimer dosage for confirmation of the diagnosis of DVT.
However, in subjects with low likelihood of thrombosis (modified Wells score < 2) a normal
D-dimer (ELISA test or equivalent) can reasonably exclude thrombosis
186
.
e compression ultrasound (CUS) of the lower limbs veins is indicated in case of abnormal values of D-dimer and in patients with high clinical probability of disease. A CUS may
however be negative in case of thrombosis of the pelvic veins and may have a non-optimal
sensitivity in subjects with symptomatic distal DVT (11-100%)
187-188
. Figure 62 illustrates a
diagnostic algorithm that employs the CUS in suspected DVT.
Venous compression ultrasonography of the lower limbs (CUS)
is assessment employs linear probes of medium to high frequency (7-10 MHz).
e patient is supine with his feet slightly sloping, in order to fill the veins of the lower limbs
His knees are slightly flexed and limbs are extra rotated in order to expose the triangle of
Scarpa and the anteromedial regions of the thigh. is position facilitates the visualization of
the iliac veins from the aortic carrefour to the inguinal ligament. e common and superficial
femoral veins are explored from the inguinal ligament to the adductor hiatus. Finally, the great
saphenous veins, including their femoral confluences are evaluated in the subcutaneous tissue.
e prone decubitus in slight anti-Trendelemburg position is ideal to explore the popliteal
veins, the veins inside gastrocnemius muscles and the small saphenous veins. Otherwise, these
vessels can be examined when the subject is in the supine position with his legs flexed, or in
a sitting position exploring the popliteal cavity and the calf.
Figure 63 illustrates how to perform lower limb venous ultrasonography in the groin and
popliteal fossa.
224 oracic ultrasound
Painful and tender edematous lower limb
Uncertain DVT
High
D-Dimer
CUS+
DVT
Figure 62 – Flow-chart with the use of CUS in patients with suspected DVT.
CUS-
NO DVT
DVT
Normal
D-Dimer
NO DVT
High
D-Dimer
CUS after 1 week
CUS+
Probable DVT
CUS-
Normal
D-Dimer
CUS-
CUS+
DVT
NO DVT
NO DVT
A
Figure 63 – A: transverse inguinal ultrasound scans; B: popliteal scan with prone patient and C:
popliteal scan with supine patient.
Many studies shows a high diagnostic accuracy of CUS for the diagnosis of DVT
B
C
189-192
. CUS
assesses the appearance of the veins investigated in two-dimensional ultrasound and their
behavior with compression through exploring probe. e principle is that normal veins have
a fluid transonic content and, if they contain no thrombotic material, completely collapse
with the pressure exerted by the probe.
e diagnosis of proximal DVT is carried out through an examination of the femoral and
the popliteal veins, including the great saphenous one with its femoral connection. ese
vessels are easy to find if the sonographer considers the local anatomy, and the relationships
between veins and the homonymous arteries, easily recognizable through their pulse and
non-compressibility. (Figs. 64-65).
We prefer to conduct a full examination evaluating the vessels at intervals of 2-3 cm. e
assessment includes the sapheno-femoral junction and the first stretch of the great saphenous
Parenchymal lung patology 225
vein. e visualization of pre-popliteal traits of the calf veins and the venous lakes inside
gastrocnemius muscles is important if the operator has sufficient skill.
Artery
Probe
Great
saphenous vein
Figure 64 – Anatomical diagram of the transverse scan on the femoral vessels in the groin. Right: color
Doppler representation.
Vein
Femoral artery
Femoral vein
Great
saphenous vein
Femoral artery
Right common
femoral vein
Figure 65 – Normal anatomy of the right inguinal region. The color Doppler facilitates the identification
of the vessels.
Especially when the limb is in a sloping position, the normal vein appears as slightly larger
than the contiguous artery. Moreover, the vein has thin walls, a transonic lumen and it dilates
when the patient performs a Valsalva maneuver or when the vessel is proximally obstructed
inducing a venous congestion. Finally, a normal vein collapses through a modest pressure of
the probe (Figs. 66-67).
226 oracic ultrasound
Right common femoral artery and vein
Artery
Compression
Figure 66 – Effect of venous compression by the probe. A: normal image of the vein and the femoral
artery in the groin. B: through compression, the common femoral vein collapses completely. The
compressibility excludes the presence of thrombosis.
Popliteal vein
Popliteal artery
Artery
Compression
Figure 67 – A: normal finding in the absence of compression. B: the compression of the patent
popliteal vein determines its complete collapse.
e compression of the iliac veins can be difficult, unless the subject is not thin. When the
patient is easily explorable even the inferior vena cava can sometimes be compressed
193
.
Parenchymal lung patology 227
On the other hand, a dilated, non-compressible vein characterizes DVT, whereas hypoechoic
luminal material may delineate an obstacle to the flow
194
(Fig. 68) (Clips 52-58).
Right internal
saphena
Figure 68 – A: great saphenous vein, patent at color Doppler. B: thrombosed saphenous vein. The
increased gauge and the presence of echogenic material in the lumen are observed. The vein is not
compressed by the pressure of the probe.
Clip 52 – Right femoral vein compressible by the probe (normality).
Thrombus
Clip 53 – Thrombosis of the left femoral vein. The vessel is not compressible
by the probe.
Clip 54 – Right popliteal vein compressible by the probe (normality).
Clip 55 – Thrombosis of the right popliteal vein, which is not compressible
by the probe.
Clip 56 – The right iliac vein is located behind the iliac artery, it shows
pulsating flow on color Doppler. The iliac vein lumen is without flow, is not
obliterated by compression and contains thrombotic material.
228 oracic ultrasound
Clip 57 – Thrombosis of the left femoral vein.
Clip 58 – Longitudinal scan of the right femoral vein. The lumen is occupied
by hyperechoic material due to fluctuating thrombus.
e assessment of echogenicity of a thrombus can differentiate a recent lesion from a past
thrombosis. In the first case the material is hypoechoic and therefore hardly distinguishable
from the blood, with smooth margins and often with a tail floating in the vessel (Figs. 69-70).
Figure 69 – Iliac-femoral venous thrombosis. The femoral vein below the inguinal ligament has
increased caliber and does not collapse, but it is difficult to distinguish the thrombotic material in the
lumen because it is poorly echogenic. Note the absence of flow on color Doppler.
Figure 70 – Thrombotic material in the lumen of the femoral vein at the level of the confluence of the
great saphenous vein (transverse scan).
Parenchymal lung patology 229
e diameter of the early thrombized vein increases and, with CUS, its lumen does not
collapse, but tends to deform as a spongy material occupies it. On the contrary, when the
thrombus is not recent its echogenicity is increased and the vessel is often contracted and
draws a rigid boundary.
CUS is the preferred diagnostic modality for the diagnosis of femoral, popliteal and large
gastrocnemius veins in ICU and Emergency Department patients (Fig. 71).
Gastrocnemius veins
Figure 71 – Effect of compression of the gastrocnemius veins (on the left). On the right, the effect of the
compression on the patent veins.
e small veins of the calf (peroneal, tibial), however, cannot be included in CUS for the
low sensitivity of this method for detecting the thrombosis in small vessels. Moreover, while
CUS specificity for DVT is high in symptomatic and asymptomatic patients, its sensitivity
is reduced in asymptomatic patients. erefore, the principal role of CUS is the easy, fast
detection of large vein thrombosis.
In this methodological optics, for the relative rarity of small and isolated segmental thrombosis
195
, some authors
196-198
propose abbreviated CUS, exploring only the common femoral
and popliteal veins (four scans).
In symptomatic patients, the sensitivity and specificity for the femoral and popliteal veins CUS
are between 90-97% and 100%, respectively
199
. erefore, in case of a negative examination
the anticoagulant therapy could be avoided, because the risk of subsequent DVT would be
around 3% or less in the following three months.
In subjects with negative proximal CUS, but with symptoms and with high probability of
DVT, it is however recommended to repeat the examination in the following 5-7 days in
order to exclude a proximal propagation of an initially localized thrombosis.
In some patients, the differentiation between recurrence of DVT and the results of a previous
thrombosis may be particularly problematic. In the year after an episode of DVT, approximately one third of patients returns with symptomatic manifestations of the affected limb.
Only a quarter of cases presents a new episode of DVT.
Clinical reasoning is determinant for an accurate discrimination of these cases. In addition
to clear signs of an old disease (e.g. luminal echogenicity, contraction of the vein, thrombus
recanalization and collateral circulation), the best guide is data comparison with previous
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