Download page1

page1
Chest Sonography
in Children: Current
Indications,
Techniques, and
Imaging Findings
After plain radiography, CT and MR imaging are •
the usually preferred modalities for imaging the
pediatric chest.
With acoustic limitations imposed by bone and air,
the thorax at first seems unforgiving place to
perform ultrasound (US
Various diseases and pathologic conditions,
however, can allow an acoustic window into the
chest, and the unique anatomy of the pediatric
chest provides other imaging windows for
creative sonologists.
Advances in thoracic US relying on interpretation of
artifacts produced by the interface of air in the
lung and pleural space allow important
information about the lung itself to be
determined by US.
US will never replace CT and MR imaging, but it can
provide important and at times superior
information safely and efficiently, particularly in
pediatric patients.
.
TECHNIQUE
Although US of the chest may be the first •
imaging modality used in some acute and
critical care settings, in general, pediatric
patients undergoing sonographic examination
of the chest have a preceding plain
radiographic examination.
This helps focus the US study and the combination of
information obtained can improve diagnostic accuracy.
As with sonography elsewhere in the body, the appropriate
transducers and frequencies vary with the size of the
patient and the structure examined.
Neonates and small infants are easily examined with highfrequency linear transducers, whereas older children and
adolescents require lower-frequency transducers.
Smaller footprint sector, vector, or tightly curved array
transducers are needed to insonate between ribs, below
the diaphragm, or from the suprasternal notch.
Linear transducers are valuable for examining chest wall
lesions and for examining the lung pleura interface.
•
•
•
•
•
Basic B-mode real-time US is generally all that is
required for chest US.
The use of M-mode imaging has proved helpful,
however, in the evaluation of pneumothorax and
quantification of diaphragmatic motion.
Color Doppler can be useful when evaluating
peripheral parenchymal opacities to differentiate
vascularized lesions from infarcts.
Useful acoustic windows are shown in Fig. 1
•
•
•
•
Fig. 1. Acoustic windows for thoracic sonography:
1, supraclavicular; 2, suprasternal; 3, parasternal;
4, transsternal; 5, intercostal; 6, subxyphoid; 7,
subdiaphragmatic;
and 8, posterior paraspinal. (Adapted
from Kim OH, Kim WS, Min JK, et al. US in the
diagnosis
of pediatric chest disease. Radiographics 2000;20:
653–71; with permission.)
•
•
•
•
•
•
•
The relatively unossified thorax of the neonate and
infant, along with the presence of a relatively large
thymus allow imaging of the anterior chest and
mediastinum through sternal and costochondral
cartilages.
Suprasternal or supraclavicular approaches may also
be useful in examining the anterior mediastinum and
thoracic vessels.
Intercostal scanning allows imaging of the lung and
pleura throughout the thorax and of the posterior
mediastinum.
•
•
•
•
The inferior thoracic cavity can be examined using •
the liver, spleen, or fluidfilled stomach as acoustic
windows.
For evaluation of the lung and pleural space in •
critically ill patients, a systematic organized
approach is required.
One suggested approach divides each •
hemithorax into 4 quadrants: upper anterior,
lower anterior, upper lateral, and basal lateral2;
the anterior axillary line divides the anterior from
lateral regions (Fig. 2)
Fig. 2. Locations of lung survey imaging. The chest is
divided into anterior and lateral portions by the
anterior
axillary line: 1, anterior superior; 2, anterior basal;
3, lateral superior; and 4, lateral basal. (Adapted from
Volpicelli G, Silva F, Radeos M. Real-time lung
ultrasound
for the diagnosis of alveolar consolidation and
interstitial syndrome in the emergency department.
Eur J Emerg Med 2011;17:63–72; with permission.)
•
•
•
•
•
•
•
•
If a patient’s condition permits, •
upright posterior imaging should be •
performed to better evaluate the posterior
chest and to improve detection of small
pleural effusions.
INDICATIONS
The most common indication for chest •
sonography is to evaluate an opacity detected
on a chest radiograph. In the case of a
completely opacified hemithorax,
US can differentiate whether parenchymal or •
pleural disease (or both) is the cause (Fig. 3).
Fig. 3. (A) Newborn with respiratory distress and
opaque left hemithorax of unclear etiology. (B)
Longitudinal
parasternal sonogram shows a large anechoic
effusion (E) and consolidated left lung (L). The
diaphragm is
partially everted, displacing the spleen (S).
Aspiration revealed a chylothorax. (Adapted from
Coley BD. Pediatric
chest ultrasound. Radiol Clin North Am
2005;43:405–18; with permission.)
•
•
•
•
Such information is often helpful for guiding the appropriate
direction of therapy and possible thoracic intervention.
Focal masses can be imaged to determine location and whether
they are solid or cystic
. Abnormal mediastinal contours in infants are usually due to an
unusually sized or shaped thymus, which can be easily shown by
US,obviating CT.
Palpable chest wall lesions are best initially imaged with US,
because nonpainful pediatric chest wall masses are typically benign
and require no further investigation.
Although CT and MR angiographic techniques can produce
exquisite vascular images, US is often the first and only necessary
study for examination of suspected thromboses and other
abnormalities of thoracic vasculature.
•
•
•
•
•
NORMAL ANATOMY
Unossified costochondral and sternal cartilage •
appears hypoechoic on US (Fig. 4). •
Fig. 4. Normal costosternal junction.
Sonogram along
the long axis of an anterior rib in a teenager
shows
the bony portion of the rib (R) with posterior
acoustic
shadowing and the hypoechoic cartilaginous
rib
end (C).
•
•
•
•
•
The shape of costochondral cartilage is often varied and may
produce irregular chest wall “masses.”
With aging, these cartilages gradually ossify, diminishing acoustic
access to the thorax.
The thymus is larger compared with the rest of the thorax during
the first year of life.
The thymus is physically largest, however, during adolescence.
Usually confined to the anterior mediastinum, the thymus may
extend into the neck or middle and posterior mediastinum, which
may produce concern for pathology.
Fortunately, the thymus has a characteristic echotexture, with
regular linear and punctate echogenicities that allows its confident
recognition and differentiation from mediastinal pathology (Fig. 5).
•
•
•
•
•
•
Fig. 5. Normal thymus. Right parasternal longitudinal
view shows a normal triangular-shaped right thymic
lobe (arrowheads) with characteristic linear and
punctate
echogenicities conforming to the contours of the
brachiocephalic vein (V) and main pulmonary artery
(PA). Note the hypoechoic costosternal cartilages (C).
•
•
•
•
•
•
The normal pleural space contains a tiny amount
of fluid,27,39 but fluid is seen with US in only
35% of
normal healthy children.39 The acoustic interface
of the chest wall with normal aerated lung
provides
a strong reflective surface and produces a
characteristic
reverberation within the US image, often
referred to as A lines (Fig. 6).
•
•
•
•
•
•
•
Fig. 6. Normal chest wall/lung interface; A lines.
Transverse intercostal sonogram using a linear
transducer
shows the strong echogenic interface of the
aerated lung and pleura (arrows) as well as the
reverberation
artifacts projected within the deeper lung
parenchyma (A lines) (arrowheads).
•
•
•
•
•
•
The thinner chest wall of infants and small •
children, however, may not demonstrate this
artifact
. Aerated lung is also seen to move along the •
parietal pleural surface with respiration,
termed the gliding sign.
Using M mode, the normal motion of the lung
produces a characteristic pattern, termed the
seashore sign (Fig. 7).16
Fig. 7. Normal chest wall/lung interface;
seashore sign.
Transverse intercostal gray-scale and M-mode
image
shows a normal lung interface (arrows) and a
normal
A line (arrowhead). In the M-mode image, the
normal
motion of the lung ([ ]) gives a pattern some
liken to
sand on a beach, thus the term seashore sign.
The recent literature is replete with many •
other terms, which often are more confusing
than clarifying. Recognizing these normal
findings, however, is important, because
deviations from their appearances provide
clues to pleural and parenchymal disease.
THE PLEURAL SPACE
Effusions
Being superficial to normally echogenic aerated lungs, the pleural
space is well visualized by US.
Although pleural fluid collections are often suspected from chest
radiographs, US is more sensitive in detecting pleural fluid than
chest radiographs, particularly in critically ill patients in whom
upright or decubitus radiographs are not possible.
The sonographic appearance of pleural fluid depends on its
composition and may range from completely anechoic, in the case
of simple transudative collections, to collections with mobile
echogenic debris in cases of infection and hemorrhage, to septated
and more solid appearing collections with empyemas and
organizing infection
(Fig. 8).
•
•
•
•
Fig. 8. Sonographic appearances of pleural collections.
(A) Subdiaphragmatic longitudinal sonogram shows
a mostly anechoic left pleural effusion (E) along with
consolidated lung (L). The spleen (S) and kidney (K)
help
to provide acoustic windows into the inferior chest. (B)
Empyema with the formation of fibrinous septations.
(C) Well-organized, solid-appearing empyema (E)
adjacent to aerated lung (L). (Adapted from Coley BD.
Pediatric
chest ultrasound. Radiol Clin North Am 2005;43:405–
18; with permission.)
•
•
•
•
•
Simple nonloculated collections can be seen •
to change shape with patient breathing or
change in position. The distinction of
echogenic but still fluid collections from more
solid collections can be aided by the fluid
color sign, in which mobile debris produces
signal with color Doppler whereas nonmobile
solid material does not.
As infected pleural collections progress and organize,
fibrinous strands begin to form.
Initially thin and mobile, these fibrin strands thicken
and increase, creating multiple loculations in which
fluid no longer changes with patient position or
respiration.
The parietal and visceral pleura may be thickened as
well, as often seen with CT.
Infected pleural collections may progress to solidify
into a homogenous echogenic gelatinous mass
encasing the underlying lung, eventually producing a
fibrothorax.
•
•
•
•
US is superior to CT in characterizing the •
nature of pleural fluid collections and can help
guide percutaneous drainage Simple fluid
collections are amenable to percutaneous
aspiration and are most safely performed with
US guidance
(Fig. 9). •
Fig. 9. Pleural effusion aspiration. Transverse
intercostal
sonogram of the left chest shows a pleural
effusion
(E) with some echogenic material. The
aspirating
needle (arrow) is seen just entering the
pleural space.
S, spleen.
•
•
•
•
•
Because up to 50% of pediatric parapneumonic •
effusions recur after aspiration, however, it is
often more prudent to leave a drainage catheter
in place, even if only for a short time.
The US detection of fibrinous strands and even •
honeycombing of the pleural space is not a
contraindication to percutaneous drainage, but it
does mean that fibrinolytic therapy is required to
clear the collections and should be started
promptly to achieve proper drainage
(Fig. 10). •
Fig. 10. Septated parapneumonic effusion.
Longitudinal
sonogram of the left chest shows consolidated
lung (L) and complex partially septated fluid
(asterisks).
This collection responded well to
interventional
drainage and lytic therapy. K, kidney; S,
spleen.
•
•
•
•
•
In the setting of continued fevers and poor •
clinical response after pleural drainage, plain
radiographs may not adequately assess
whether undrained pleural collections or
underlying parenchymal infection is the cause,
US can adequately assess the pleural space
and portions of the underlying lung, although
there may be limitation from existing chest
tubes, dressings, and patient discomfort.
In these complicated and refractory cases, CT •
may be a better option, especially if surgical
Masses
Malignant disease involving the pleural space •
is much less common in children than in
adults54 but ca occur with Wilms tumor,
neuroblastoma, leukemia, and sarcoma
Primary chest wall neoplasms and pleural •
metastases are often accompanied by
hemorrhagic pleural effusions, which appear
as echogenic debris-filled fluid at sonography.
The presence of pleural fluid aids in detection •
of solid masses adherent to the parietal or
visceral pleura (Fig. 11).
Fig. 11. Longitudinal sonogram of the right
chest in
a child with Wilms tumor shows a pleural
effusion
(E) outlining a metastatic deposit on the
diaphragmatic
parietal pleura (arrow). (Adapted from Coley
BD. Pediatric chest ultrasound. Radiol Clin
North Am
•
•
•
•
•
If visible sonographically, pleural masses are •
readily biopsied with US guidance (Fig. 12),
allowing confirmatory histologic diagnoses
Fig. 12. Pleural biopsy. Intercostal sonogram in
a child
with Wilms tumor shows a pleural-based solid
mass
(arrowheads). The aspirating needle (arrow) is
seen
within the lesion, and yielded metastatic
Wilms
tumor
•
•
•
•
•
Pneumothorax
As discussed previously, the normal stron
acoustic interface between pleura and aerated
lung produces repeating posterior echogenicities
(A lines), and the normal sliding motion of the
lung can be seen during respiration (see Fig. 6)
.
When air is introduced into the pleural space, the
normal tension between the pleural layers is lost,
and a gap is created between the parietal and
visceral pleura disrupting the normal acoustic
interface
. The sliding of the underlying lung can no longer
be seen, and the normal reverberation is
•
•
•
•
Fig. 13. Pneumothroax. Transverse intercostal
sonogram
shows a normal pattern of moving lung
(seashore sign) deep to the lung pleural
interface
(arrow). On the right hand side of the image,
there
is loss of this normal pattern with a static
series of
horizontal echogenicities. Note how this looks
•
•
•
•
•
•
Some reports indicate that US is superior to •
plain radiographs in pneumothorax detection
and may be useful in monitoring procedural
complications and assessing critically ill and
trauma patients.
Similarly, the curtain sign has been described •
in hydropneumothorax where the normal
pleural gliding is lost and mobile air fluid levels
are visualized.
LUNG PARENCHYMA
Interstitial Disease
Plain radiography usually suffices for the evaluation of •
parenchymal lung disease in pediatric patients, but
unclear cases may benefit from US or CT examination.
The traditional view is that aerated lung must becom •
atelectatic or consolidated before it becomes possible
to examine with US.
More recent studies have shown that there is •
significant important clinical information that can be
obtained by evaluating the artifacts produced from the
surface of aerated lung.
The interaction of the sound beam with interlobular •
septa produces so-called B lines, also referred to as
A few scattered B lines can be normally seen and may
be caused
by focal subpleural thickening or distortion by
parenchymal disease.
Multiple B lines can indicate an abnormality with the
underlying lung.
Anything that thickens the interlobular septa can
produce a B line, but the distinction between fibrotic
change and interstitial edema can often be made given
the clinical context.
In adults, this finding has been shown with a variety
of disorders, such as pulmonary fibrosis, viral
pneumonias, sarcoidosis, lymphangitic
•
•
•
•
•
Investigators have subdivided B lines into B7 •
lines (7 mm apart), indicating thickened
interlobular septa, and B3 lines (3 mmapart),
indicating the equivalent of the ground glass
appearance at CT.
The presence of B lines is shown to correlate •
accurately with other imaging, pulmonary
artery pressures, and fluid status and seem
accurate in diagnosing interstitial and alveolar
disease.
Experience in children is more limited, •
particularly
regarding interstitial edema,68 but my
anecdotal experience indicates that similar
findings occur in children as well (Fig. 14).
Fig. 14. Interstitial edema. (A) Chest radiograph of
a teenage girl with dyspnea and new-onset renal
failure
shows interstitial edema. (B) Longitudinal image
of the right upper quadrant shows an abnormally
echogenic
kidney consistent with the subsequent diagnosis
of glomerulonephritis. Note the regularly spaced
B lines within
the right lower lobe (arrowheads). These
correspond to the thickened interlobular septa
•
•
•
•
Surfactant deficiency disease produces •
variable appearances ranging from multiple B
lines to a diffusely echogenic lung, which
eliminates visualization of the normal chest
wall–pleural interface
(Fig. 15). •
Fig. 15. Surfactant deficiency disease. (A)
Chest radiograph of a preterm infant shows
diffuse granular airspace
disease typical of surfactant deficiency, worst
in the right lower lobe. (B) Transverse
sonogram of the right lower
chest through the liver (L) shows abnormal
increased pulmonary echogenicity of the right
lower lobe without
visualization of focal B lines.
•
•
•
•
The sonographic appearance correlates well •
with the clinical and radiographic findings.71
Chronic lung disease in the infant produces
similar acoustic interfaces as seen in adult
parenchymal disease, creating multiple ringdown artifacts (Fig. 16).
Fig. 16. Chronic lung disease. (A) Portable
chest radiograph in a former preterm infant
with continued oxygen
requirements shows increased interstitial
markings of chronic lung disease. (B)
Longitudinal sonogram through
the left upper quadrant shows multiple B lines
indicating interstitial lung disease. (Adapted
from Coley BD. Pediatric
chest ultrasound. Radiol Clin North Am
2005;43:405–18; with permission.)
•
•
•
•
The progression of US findings from surfactant •
deficiency to bronchopulmonary dysplasia may
be useful as a predictor of the development of
chronic lung disease and may appear earlier than
chest radiographic findings.
The administration of exogenous surfactant, •
however, does not seem to improve the
sonographic appearance in surfactant deficiency.
Interstitial prominence causing B lines persists, •
indicating that interstitial extravascular fluid
clearance remains impaired despite radiographic
Consolidation
Airless lung can appear sonographically similar •
to liver, thus has been termed, hepatization
(Fig. 17).
Fig. 17. Lung consolidation. Longitudinal
sonogram
over the lower right chest shows consolidated
lung
superior to the liver. Although their
echogenicities
differ, their internal sonographic appearance is
similar. (Adapted from Coley BD. Pediatric
chest ultrasound.
•
•
•
•
•
The underlying internal architecture of the •
lung is preserved, however, allowing
differentiation from masses or other
processes. Branching linear echogenicities
representing air bronchograms are often seen
(Fig. 18)