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20 Contrast-Enhanced Ultrasound inPediatric Intervention
247
sulfur hexauoride lipid. If an immediate repeat
examination is necessary, the UCA may either be
aspirated out of the cavity or the microbubbles
burst by repeated high mechanical index (MI)
pulses, before a fresh injection.
20.3 Applications
With either the intravascular and intracavitary
applications, the distribution of UCA within the
target improves visualization of the region of
interest and provides valuable guidance during
the procedure. Besides, CEUS is often used as a
problem-solving tool to guide decisions in patent
management after completion of the procedure.
20.3.1 Intravascular Applications
Microbubbles within the UCA measure 2–6μm
in diameter, and when administered in the blood
pool, UCA remains in the blood pool without
entering the interstitial space, and therefore offers
an excellent characterization of the “target”
vascularity.
20.3.1.1 Biopsy
A primary application of CEUS in interventional
radiology is biopsy guidance. A UCA is sometimes useful to increase the conspicuity of the
lesion, given the lower contrast resolution of
grayscale US relative to computed tomography
(CT) or magnetic resonance (MR) imaging. This
may be particularly useful for small lesions in
homogeneous solid viscera such as the liver. In
children, this is frequently in the setting of concern for metastasis, as primary liver neoplasms,
while uncommon, are frequently large at presentation and readily visible on conventional sonography. More frequently, CEUS is used in biopsy
guidance to determine the optimum site of biopsy
within the tumor, as enhancement indicates most
viable regions of the tumor. Biopsy of nonnecrotic regions would increase diagnostic yield
(Fig.20.1). Acquisition of viable tissue may be of
a
b
Fig. 20.1 (a) A split-screen display of a CEUS examina-
tion (left: grayscale. Right: CEUS) demonstrates a mass
in the right lower quadrant of the abdomen. An area of
necrosis, demonstrated as a non-enhancing area within the
mass, is demonstrated on CEUS (arrows). (b) On
US-guided biopsy, the necrotic area within the lesion was
avoided, guided by the CEUS ndings
248
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A. Srinivasan and D. Y. Huang
particular concern if genetic analysis of tissue for
next-generation sequencing is desired. The use of
CEUS can shorten the procedure, as it can
increase the condence of adequate sampling,
thereby decreasing the number of passes the
interventionist would make, and also decrease
the need for frozen section analysis during the
procedure. Similarly, the assessment of perfusion
during a biopsy can help avoid large vessels
coursing through or around the tumor, therefore
decreasing the risk of hemorrhage after a biopsy.
If there is a concern for signicant post- procedure
hemorrhage, this can be assessed by CEUS of the
region of intervention, often faster and with less
logistical complexity than CT [5]. The excellent
depiction of vasculature allows for the easy
detection of pseudoaneurysms [6].
CEUS may also be used to guide decisions
during the procedure, and this aspect would apply
diagnostic principles of CEUS. Illustrative scenarios include use of CEUS to distinguish complex uid collections (which may have a
questionable solid appearance on the grayscale
US) from solid tumors, and this would determine
whether the procedure is a drainage or a biopsy,
without having to perform a CT or MR examination (Fig. 20.2). Furthermore, based on the
enhancement pattern, a lesion may be demonstrated to be benign in the interventional suite,
therefore obviating the need for biopsy [1].
20.3.1.2 Interventional Oncology
Interventional oncology, the application of
interventional radiology towards targeted
destruction of tumors, is an established pillar
of cancer therapy in adults, and these techniques, while less frequently indicated in children, are gaining recognition in pediatric
oncology. A practical application of CEUS
would be for intra- procedural and post-procedural feedback: tumor vascularity is assessed
before and after ablation (radiofrequency ablation, cryoablation, microwave ablation, ethanol ablation, high-frequency focused
ultrasound, and irreversible electroporation).
The demonstration of cessation of contrast
enhancement provides strong conrmation of
the adequacy of treatment (Fig.20.3), and the
lack thereof would indicate further ablation is
necessary. Contrast-enhanced ultrasound provides superior spatial and temporal resolution
of tissue perfusion than other modes of crosssectional imaging. In adults undergoing ablation of hepatoma, the absence of perfusion
after ablation has shown to be highly predictive
of therapeutic success, and residual tumor
detection is at least commensurate with other
imaging modalities [5]. Immediate post-ablation assessment of tissue perfusion is best
suited for cryoablation, as a collection of gas in
the treatment area from tissue vaporization will
Fig. 20.2 (a) Color Doppler US examination in a boy
with a history of neuroblastoma revealed an indeterminate
hypoechoic focal abnormality. (b) CEUS performed in the
interventional suite showed the rim-enhancement of the
lesion, consistent with abscess, and a drainage, instead of
a biopsy, was performed
20 Contrast-Enhanced Ultrasound inPediatric Intervention
a
b
249
Fig. 20.3 (a) A split-screen display of a CEUS examina-
tion (left: grayscale. Right: CEUS) in a 3-year-old male
demonstrates a metastatic rhabdomyosarcoma at the right
shoulder. The lesion demonstrates enhancement (arrows)
relative to the surrounding structures on CEUS, and there
hinder US assessment immediately after radiofrequency or microwave ablation [5]. Similarly,
intra-arterial administration of UCA has been
used to guide embolization (conrm appropriate sub-selectivity) and to determine adequacy
treatment during trans-arterial embolization of
liver tumors [7].
20.3.1.3 Vascular Access
CEUS may be used for planning in cases of challenging venous access. Patients with a history of
multiple or long-term central venous access often
develop central venous stenosis or occlusion.
was early washout. (b) A split-screen display of a CEUS
examination (left: grayscale. Right: CEUS) was performed immediately following cryoablation, showing
absence of enhancement of the ablated lesion and indicating a successful ablation
Smaller children are particularly susceptible to
these complications, as the catheter occupies a
larger cross section of the venous lumen, reducing ow and predisposing to thrombosis and intimal hyperplasia, which then evolves to stenosis
or occlusion. This can signicantly complicate
venous access [8]. To date, at-risk patients are
commonly assessed by CT or MR venography,
interventional venography, or Doppler sonography. CEUS venography may demonstrate central
venous stenosis to good advantage (Fig. 20.4)
and has the added benet of ease-of-use and the
lack of ionizing radiation.
250
A. Srinivasan and D. Y. Huang
ab
Fig. 20.4 (a) CEUS and the corresponding (b) venography of the left subclavian vein. Both examinations demonstrate
a focal stenosis (block arrow) at the distal left subclavian vein
20.3.2 Intracavitary Applications
The distribution of the contrast agent within a
cavity can provide valuable information to determine the adequacy of intervention and postprocedure management. Endocavitary CEUS can
also be used as a problem-solving tool to assess
complications related to interventions (e.g., catheter dislodgement) or the underlying disease process (e.g., stula formation). These applications
often enhance or supplant conventional uoroscopic or CT techniques, and can facilitate the
care of critically ill children, as they can be performed at the bedside and also without ionizing
radiation. While some of these applications may
be performed with agitated saline infusion and
the grayscale US, CEUS offers improved visualization and the ability to see delayed lling of
communications and compartments, as the
microbubbles in the UCA are more stable than
those of agitated saline [3].
20.3.2.1 Drainage
CEUS gives an excellent denition of the cavity
size and shape. Large abscesses are often multiloculated and may require multiple drains. After
the initial catheter placement, demonstrated lling of the entire volume of a multiloculated collection may conrm procedure endpoint without
uoroscopy, and obviate the need for additional
catheter placement.
Concerning management post-procedure,
CEUS of the drained cavity can be used to verify
the position of the drain, demonstrate stulous
communication, and characterize the state of the
cavity before drain removal (Fig. 20.5). For
example, inammatory collections such as empyema contain complex proteinaceous material that
forms membranes/loculations and greatly
increase uid viscosity, limiting the efcacy of
drainage. The uid can be mobilized by intracavitary infusion of a brinolytic agent (e.g., urokinase or tissue plasminogen activator), but the
response to brinolysis must be monitored to
ensure adequate management. The progress of
adequate brinolysis can be assessed with good
condence by infusion of UCA into the cavity
(Fig.20.6). In cases of high or abnormal output
after drainage, CEUS provides an excellent
depiction of stulae and can be used to track resolution. CEUS can be easily performed at the
bedside and allows imaging in multiple planes
with greater spatial and contrast resolution than
uoroscopy.
20.3.2.2 Sclerotherapy
Endocavitary CEUS can minimize or obviate the
use of uoroscopy for certain slow-ow vascular
20 Contrast-Enhanced Ultrasound inPediatric Intervention
ab
251
Fig. 20.5 (a) CT images of a multi-loculated pelvic
abscess (arrows). (b) A split-screen display of an intracavitary CEUS examination (left: grayscale. Right:
a b
c
CEUS) conrms adequacy of treatment from a single
trans-rectal drain, with all loculations within the collection lled with microbubbles after instilling the contrast
Fig. 20.6 (a) A chest radiograph demonstrates a left
empyema with a pleural drain in situ. (b) A split-screen
display of an intracavitary CEUS examination (left:
CEUS.Right: grayscale), with contrast instilled through
the pleural drain, demonstrates a loculated empyema, with
microbubbles conned within a loculated collection
around the pleural drain (arrows). (c) Following brinolytic infusion through the pleural drain, a repeat intracavitary CEUS (left: CEUS grayscale. Right: grayscale;
coronal image) demonstrates microbubbles diffusing
through the pleural space
252
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c
A. Srinivasan and D. Y. Huang
d
Fig. 20.7 (a) A T2-weighted MRI image showing the
high signal intramuscular vascular malformation (arrows).
(b) The grayscale US image demonstrates an intramuscular vascular malformation at the right shoulder as mixed
echogenicity areas in the subcutaneous tissue. (c, d)
CEUS (left) and corresponding uoroscopic (right)
malformations (specically, lymphatic and nondiffuse venous malformations which lack robust
outow into deep veins). Using principles similar
to those highlighted with drainage, the distribution of UCA in the malformation can be used to
determine whether all components of the malfor-
images during CEUS-guided sclerotherapy. CEUS can be
used to assess for complete treatment, as injection into
separate sites shows microbubble lling of the different
compartments of the larger lesion, as depicted on the uoroscopic images (curved arrows and arrowheads)
mation have been lled. If areas of the malformation do not ll with UCA, this would mandate
separate access to these areas (Fig.20.7). CEUS
allows excellent characterization of the lesion
before installation of the sclerosant; the sclerosant is often constituted as a foam, and once it
20 Contrast-Enhanced Ultrasound inPediatric Intervention
253
is injected, the lesion may no longer be adequately seen on the US.
In instances of sclerotherapy of cysts that
are not strictly vascular malformations, CEUS
may be useful in documenting the lack of communication with normal parenchyma. For
example, this utility may be benecial in
sclerotherapy of a symptomatic renal cyst if
there is a question of communication with the
collecting system, before instilling an offending sclerosant (Fig.20.8).
instilling UCA into the needle before access
improves needle visualization. With successful
access to the renal collecting system, the UCA
will ow away from the needle and ll the calyx,
allowing access with the US instead of uoroscopy. However, if UCA is injected without adequate access to the calyx or a bile duct, the UCA
will remain in the parenchyma, but stagnant
microbubbles can be destroyed with high MI
scanning. Therefore, a failed access attempt will
not result in a “blob” that impedes visualization
in subsequent attempts, as can be encountered
20.3.2.3 Urinary andBiliary Tracts
Access to non-dilated collecting systems can be
greatly aided by CEUS [9]. As described above,
with uoroscopy [6].
Once access is obtained, CEUS cholangiogra-
phy or antegrade nephrostogram (Fig.20.9) can
ab
c
Fig. 20.8 (a) A coronal T2-weighted image of the abdo-
men and (b) a grayscale US image of the left kidney demonstrate a large cystic structure within the left kidney
(arrows). (c) A split-screen display of an intracavitary
CEUS examination (left: CEUS. Right: grayscale) conrms no communication (arrowheads) between this cyst
with the renal collecting system. The CEUS nding permits sclerotherapy to be safely performed
254
A. Srinivasan and D. Y. Huang
ab
c
Fig. 20.9 (a) A coronal MR cholangiogram image dem-
onstrates biliary dilation and cystic duct debris (arrow) of
Mirrizi syndrome. (b) A biliary drain and percutaneous
cholecystostomy were placed. (c, d) Resolution of the
obstructing debris was followed with bedside CEUS
(split-screen display, left: CEUS.Right: grayscale) with
contrast owing into the cystic duct and duodenum (open
arrows)
20 Contrast-Enhanced Ultrasound inPediatric Intervention
d
Fig. 20.9 (continued)
255
be performed, with all the previously described
advantages over uoroscopy. The ureter and the
site of any obstruction can be well visualized, as
can the central biliary ductal system—UCA can
also be followed into the small bowel (Fig.20.10)
[5]. As with drainage of other collections, CEUS
can be used to assess post-procedure complications such as catheter dislodgement, leakage, stula, and hemorrhage.
20.3.2.4 Other Intracavitary
Applications
Myriad other endocavitary applications have
been described. In the enteric system, a UCA
enema may be performed with primary gastrostomy placement to delineate the large bowel in
relation to the stomach. The advantage over uoroscopy is that one can easily determine whether
the colon is supercial or deep to the stomach.
Injection of UCA into the stoma can conrm
appropriate tube placement and assess complications [10].
Additional applications of “endocavitary”
CEUS include assessment of ducts of the parotid
glands (CEUS sialography). Contrast-enhanced
ultrasound access techniques can also be
employed to access joints for steroid injections in
children with juvenile idiopathic arthritis.
256
A. Srinivasan and D. Y. Huang
ab
c
Fig. 20.10 Images from (a) uoroscopic and (b) US
contrast injection of a cecostomy tube in a teenager with
constant fecal leakage from the site. (c) CEUS of tract
20.4 Conclusion
Contrast-enhanced ultrasound is an asset to interventional radiology and offers manifold advantages that can facilitate the procedure and enhance
patient care. While currently US contrast is best
indicated for biopsy guidance, ablation control, and
follow-up and drainage procedures, these are by no
means limitations to the impactful use of CEUS in
pediatric interventions. With added experience,
new applications will undoubtedly be found, and
these would only be bounded by the inventiveness
of the enterprising interventional radiologist.
injection after tube removal shows two parallel tracks
(arrows). One of the tracks is the stoma and the other an
enterocutaneous stula
References
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652–64.
2. Dietrich CF, Averkiou M, Nielsen MB, Barr RG.How
to perform contrast-enhanced ultrasound (CEUS).
Ultrasound Int Open. 2018;4:E2–E15.
3. Muller T, Blank W, Leitlein J, Kubicka S, Heinzmann
A. Endocavitary contrast-enhanced ultrasound: a
technique whose time has come? J Clin Ultrasound.
2015;43:71–80.