AJR 2005; 184:1150-1156
© American Roentgen Ray Society
Contrast-Enhanced Sonography of the Spleen
Orlando Catalano,
Fabio Sandomenico1,
Iolanda Matarazzo1 and
Alfredo Siani2
1 Department of Radiology, S. Maria delle Grazie Hospital, Via Domitiana
Località La Schiana, Pozzuoli (Na) I-80078, Italy.
2 Department of Radiology, I.N.T. "Fondazione Pascale," via
M.Semmola, Naples I-80131, Italy.
Received July 4, 2004;
accepted after revision September 9, 2004.
Address correspondence to O. Catalano.
Abstract
OBJECTIVE. Combined use of low-mechanical-index technologies and
non-air-filled contrast media allows real-time sonographic assessment of the
spleen. This pictorial essay focuses on several aspects of contrast-enhanced
sonography of the spleen, including examination technique, clinical
indications, normal findings obtained through all vascular phases, abnormal
findings (splenomegaly, infarction, abscess, benign tumors, lymphoma,
metastasis, injuries, and accessory spleen), limitations, and pitfalls.
CONCLUSION. Real-time, contrast-enhanced sonography is a novel
technique allowing depiction of a wide range of splenic abnormalities.
Introduction
Low-mechanical-index contrast-specific sonography is a new technique
allowing real-time, gray-scale imaging during contrast medium circulation
[1]. In our institution,
contrast-enhanced sonography is frequently used when the baseline is believed
or shown to be inadequate for proper splenic assessment. Use of this technique
will probably increase in the future and radiologists should be familiar with
the findings. This pictorial essay illustrates the contrast-enhanced
sonographic features of a wide spectrum of splenic abnormalities.
Examination Technique
We use a contrast-dedicated mobile machine (EsaTune, Esaote) with harmonic
technology contrast-tuned imaging (CnTI) and a multipurpose machine (Technos,
Esaote) with a convex phased-array 3.5-MHz transducer (CA430) with multiple
tight bands. This software produces images on the basis of both maintenance of
microbubbles at low acoustic pressure and subtraction imaging
[2].
We rapidly injected via IV the sulfur hexafluoride-based contrast agent BR1
(SonoVue, Bracco) at a 2.4- to 4.8-mL volume. In our country, SonoVue has no
defined contraindication because side effects are uncommon. Injection of this
contrast agent can be immediately repeated, although this procedure was
required very rarely in our experience. Continuous scanning starts immediately
and lasts 1-6 min. A very low acoustic pressure (0.06-0.08 mechanical index)
is used, with the sound beam focused at the deeper aspect of the interest
region. Periodically, the operator may add a higher level acoustic flash to
the ongoing continuous acquisition, briefly breaking microbubbles within the
insonated volume. This allows a kind of enhancement resetting, different from
high-mechanical-index intermittent imaging.
Indications
Probably more than other sonographic techniques, contrast-enhanced
sonography is operator-dependent, requiring significant specific experience to
be applied to clinical practice. In our institution, radiologists directly
perform both conventional and contrast-enhanced sonographic examinations
[2].
In our country, sonography is used extensively in imaging the abdomen,
being frequently used as the first choice for an abdominal survey.
Consequently, there is also a significant use of contrast-enhanced sonography.
In most instances, the radiologist chooses an immediate contrast-enhanced
study, in addition to conventional sonography of the spleen, either because of
detection of a definite abnormality requiring further assessment or because of
a subtle change in the parenchymal echo pattern, whether or not due to a real
abnormality. In a minority of cases, it is now the referring clinician who
calls for a contrast-enhanced sonographic study. For example,
contrast-enhanced sonography has become part of patient follow-up in
hematologic malignancies at our institution
[2].
We use sonography (focused to both peritoneal fluid and abdominal organs)
for initial screening of trauma patients. Contrast-enhanced sonography is
immediately added when baseline sonography is positive for spleen injury,
baseline sonography is positive for free peritoneal fluid only, baseline
sonography is indeterminate, or baseline sonography is negative but there is
persistent clinical or laboratory suspicion. CT is used selectively as a
second-line option.
Another frequent indication for contrast-enhanced sonography in our
institution is patient follow-up
[2]. This mainly includes
monitoring of splenic injuries that are managed conservatively and assessing
therapeutic response of lymphomatous and metastatic splenic diseases.
Normal Appearance
Splenic artery opacification starts about 12 sec after SonoVue bolus
injection. Subsequently there is an inhomogeneous enhancement of splenic
parenchyma, resembling the well-known zebra-striped pattern seen on dynamic CT
or MRI [2] (Figs.
1A, and
1B). During the first minute
after injection, small arteries are seen radiating from the splenic hilum
while venous opacification is always limited. Approximately 50 sec after the
injection, splenic parenchyma becomes homogeneous, showing dense persistent
enhancement for up to 5-7 min. SonoVue produces spleen-specific enhancement
longer than the blood-pool phase, probably because of some kind of parenchymal
uptake [3]. In comparison with
the contiguous left kidney, showing intense but transient enhancement, the
spleen appears as hypoechoic during the early phase of opacification and
hyperechoic during the late phase.
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Fig. 1A. —37-year-old healthy male volunteer. S = Spleen, K = Left
kidney, D = Left hemidiaphragm. Contrast-enhanced sonogram (obtained 34 sec
after injection) shows slightly inhomogeneous enhancement of spleen
parenchyma.
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Fig. 1B. —37-year-old healthy male volunteer. S = Spleen, K = Left
kidney, D = Left hemidiaphragm. Contrast-enhanced sonogram (obtained 123 sec
after injection) shows homogeneously hyperechoic splenic texture. Note
opacified hyperechoic splenic artery (short arrow) and unopacified
hypoechoic splenic vein (long arrow).
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Abnormal Findings
Diffuse Splenic Disease
Cases with marked splenomegaly may show a slightly delayed global
enhancement, with a less-intense opacification of splenic parenchyma and a
more prolonged early-phase inhomogeneity
[2]
(Fig. 2). Nevertheless, these
changes are neither constant nor specific. More significant data may
theoretically derive from quantitative studies
[3].
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Fig. 2. —71-year-old man with chronic lymphatic leukemia and nonfocal
splenic involvement. Contrast-enhanced sonogram (obtained 125 sec after
injection) shows markedly enlarged spleen with subtle inhomogeneity. Note that
echogenicity of spleen parenchyma is lower than that in
Figure 1B. S = spleen.
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Infarction
Partial infarcts usually appear as wedge-shaped hypoechoic areas based on
the spleen capsule and pointing toward the hilum
[2]
(Fig. 3). Isoechoic or slightly
hypoechoic infarcted areas on unenhanced images become clearly hypoechoic
after contrast injection, especially on late-phase scans (Figs.
4A, and
4B). Margins can be well- or
ill-defined, and texture can be homogeneous or inhomogeneous. An abruptly
interrupted enhanced artery can be seen on early-phase scans in relation to
the infarct apex, whereas a small enhancing rim can be noted on avascular area
margins. Atypical round infarcts, sometimes resembling focal lesions on
baseline scans [4,
5], are readily diagnosed
because of absent enhancement. Near-total splenic infarction is seen as a
diffuse lack of parenchymal enhancement (possible upper pole areas of
preserved perfusion). Comparison with normally enhancing adjacent left kidney
allows diagnosis [2].
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Fig. 3. —69-year-old woman with atrial fibrillation and splenic
embolism. Contrast-enhanced sonogram (obtained 57 sec after injection) shows
wedge-shaped hypoechoic (avascular) area (arrows) pointing toward
splenic hilum (infarction).
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Fig. 4A. —50-year-old man with chronic liver disease and portal
hypertension. Contrast-enhanced sonogram (obtained 50 sec after injection)
shows splenic deeper pole hypoechoic area (straight arrows) with
slightly echoic rim and incompletely opacified afferent artery (curved
arrow). S = spleen.
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Abscess
Intraparenchymal abscess is slightly or clearly hypoechoic, especially on
late-phase images, with enhancing rim and septa. No sign of contrast
microcirculation is seen within the internal fluid, debris, and necrotic
components. Subcapsular and perisplenic abscesses are recognizable as anechoic
collections with enhancing borders
[2]
(Fig. 5).
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Fig. 5. —49-year-old man with oral floor infection and hematogenous
sepsis. Contrast-enhanced sonogram (obtained 111 sec after injection) shows
subcapsular anechoic (avascular) partially loculated homogeneous fluid
collection (arrows) of spleen (proven to be abscess at aspiration). S
= spleen.
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Tumors
Small capillary hemangiomas, homogeneously hyperechoic on unenhanced scans
[4,
5], usually show an enhancement
pattern similar to that of adjacent splenic tissue, being constantly
isoechoic. A hyperechoic lesion on baseline images that becomes undetectable
on enhanced scans is diagnosed as a hemangioma
[2] (Figs.
6A, and
6B).
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Fig. 6B. —22-year-old woman with vague abdominal pain and incidental
detection of spleen hemangioma. S = spleen. Contrast-enhanced sonogram
(obtained 62 sec after injection) fails to recognize any splenic focal
lesion.
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Larger, cavernous hemangiomas show a greater enhancement degree, with rapid
or slow opacification. Filling-in can be centripetal or diffuse (Figs.
7A,
7B,
7C, and
7D). Contrast enhancement is
very dense and prolonged, with a possible back shadowing in large
hemangiomas.
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Fig. 7A. —54-year-old man with previous colonic carcinoma and increased
tumor markers. Baseline sonogram detects splenic solitary hypoechoic lesion
(arrow). Hypoechoic splenic nodules are usually malignant
[4,
5].
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Fig. 7B. —54-year-old man with previous colonic carcinoma and increased
tumor markers. Contrast-enhanced sonogram (obtained 21 sec after injection)
shows hypoechoic nodule with thick regular enhancing rim (arrow).
Disregard black sector-shaped artifact covering middle third of spleen.
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Fig. 7C. —54-year-old man with previous colonic carcinoma and increased
tumor markers. Contrast-enhanced sonogram (obtained 133 sec after injection)
shows centripetal filling of lesion (arrow), diagnostic for
hemangioma. Disregard artifact mentioned in B.
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Fig. 7D. —54-year-old man with previous colonic carcinoma and increased
tumor markers. Contrast-enhanced CT scan correlates well with
contrast-enhanced sonogram (B) in showing lesion (arrow).
Nodule was unchanged on sonography (not shown) performed 6 months later.
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Lymphoma
Lymphoma nodules and hematogenous metastases have a similar appearance.
Both can be isoechoic (undetectable) or hypoechoic on unenhanced images
[4,
5] but become evident after
contrast medium injection as clear hypoechoic defects (Figs.
8A, and
8B). The lesion-to-parenchyma
contrast gradient increases progressively while moving to the late phase of
parenchymal opacification. Regularly deposited (usually in lymphoma lesions)
or anarchically disposed (usually in metastases) vessels can be seen first
encircling and then entering the nodule and are especially recognizable during
the early phase of opacification. Tumor tissue itself enhances less than the
surrounding parenchyma.
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Fig. 8B. —63-year-old woman with uterine carcinoma. Contrast-enhanced
sonogram (obtained 101 sec after injection) confirms perisplenic effusion
(short arrow) but in addition shows hypoechoic defect (long
arrow) due to metastasis. Liver metastases (not shown) were also
found.
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Subtle echo pollution can be seen on real-time videos during the late phase
of enhancement (Figs. 9A, and
9B). This finding is due to
microcirculation visualization, achievable with low-mechanical-index
techniques. Subtle echo pollution is especially frequent in primary and
secondary malignancies [2]. In
case of successful chemotherapy, the lesion becomes almost anechoic on
contrast-enhanced scans with absence of intranodular vessels and
microcirculation [2].
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Fig. 9B. —31-year-old man with Hodgkin's disease involving spleen.
Contrast-enhanced sonogram (obtained 53 sec after injection) clearly shows two
hypoechoic lesions (arrows). Small echoic dots within nodules appear
on real-time videos as moving pollution (microcirculation).
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Trauma
Injuries show a decreased or absent enhancement and are clearly seen as
opacification defects, better evident during the late phase of enhancement
[6,
7]. A contusion appears as
ill-defined, slightly hypoechoic areas, whereas a laceration is seen as a
clearly hypoechoic band, linear or branched, that is usually perpendicular to
the spleen surface (Figs. 10A,
10B,
11A,
11B, and
11C).
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Fig. 11B. —31-year-old man with blunt trauma. Contrast-enhanced sonogram
(obtained 177 sec after injection) shows hypoechoic band (arrows) due
to transverse complete laceration of spleen. S = spleen. K = left kidney.
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Contrast extravasation, indicating active bleeding, is detected as an
early-phase hyperechoic pool or jet within the splenic parenchyma or
perisplenic hematomas [6]
(Fig. 12). Differential
diagnosis includes calcifications (already visible on baseline images), normal
vessels (different appearance and disposition), pseudoaneurysms (limited
practical value of differentiation), and uninjured parenchymal areas within
large lesions caused by contusions and lacerations (there is a different
appearance with lower echogenicity).
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Fig. 12. —40-year-old woman with blunt trauma. Contrast-enhanced
sonogram (obtained 44 sec after injection) shows hyperechoic pooling
(arrow) of extravasated contrast medium pointing toward spleen
surface. F = perisplenic fluid, S = spleen.
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In many instances, emergent baseline sonography shows perisplenic fluid but
fails to show defined parenchymal injuries. Instead, contrast-enhanced
sonography allows direct visualization of trauma lesions
[2,
6].
Accessory Spleen
An accessory spleen has an enhancement pattern constantly paralleling that
of the adjacent spleen. On early-phase scans, a small artery can be seen
emerging from the splenic pedicle and entering perpendicularly the
correspondent accessory spleen pole (Figs.
13A, and
13B). These findings allow
differentiation from other perisplenic abnormalities
[2,
8].
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Fig. 13A. —39-year-old man with lymphoma and nonfocal spleen
enlargement. S = spleen. Contrast-enhanced sonogram (obtained 15 sec after
injection) shows feeding pedicle (long arrow) entering enlarged
accessory spleen (short arrow).
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Fig. 13B. —39-year-old man with lymphoma and nonfocal spleen
enlargement. S = spleen. Contrast-enhanced sonogram (obtained 134 sec after
injection) shows identical texture between spleen and accessory spleen
(arrow).
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Surgical Complications
Splenic recess fluid collections after splenectomy appear as an anechoic
loculation. Septic collections (abscesses) show internal strand and rim
enhancement. Postsplenectomy hematomas appear as complex nonenhancing
pseudomasses (Figs. 14A, and
14B).
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Fig. 14A. —23-year-old woman with acute anemia 12 hr after splenectomy
for spleen injury. Baseline sonogram shows ill-defined and inhomogeneous left
subphrenic pseudomass (arrows). K = left kidney.
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Fig. 14B. —23-year-old woman with acute anemia 12 hr after splenectomy
for spleen injury. Contrast-enhanced sonogram (obtained 28 sec after
injection) shows contrast pooling (curved arrow) adjacent to large
hematoma (straight arrows). Active bleeding from splenic pedicle was
found at surgery.
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Limitations of Contrast-Enhanced Sonography
Some limitations of splenic sonography clearly also persist on
contrast-assisted studies, including difficulty in imaging deep pole and
subphrenic regions, partial need for patient inspiration, and possible
shadowing from left colonic flexure. In addition, because most splenic
abnormalities are hypovascular (hypoechoic) after contrast injection, lesion
characterization is only partially improved on contrast-enhanced studies
(although the same limitation may be applied to CT and MRI of focal splenic
lesions and pseudolesions).
Pitfalls
There are also some potential pitfalls. During the early phase of
parenchymal opacification, the spleen may appear inhomogeneous, but the
transient nature of eventual pseudolesions allows proper assessment. Densely
opacified superficial portions of splenic parenchyma may transiently obscure
deeply located ones. Finally, opacified arteries may resemble contrast
pooling.
Although sonography has a limited intrinsic field of view,
low-mechanical-index imaging allows enough time to explore accurately the
enhanced splenic parenchyma, even in case of severe splenic enlargement.
Summary
The spleen is very well suited for contrast-enhanced sonography, being
normally superficial, small, and homogeneous (except for small vessels
adjacent to the hilum) and showing intense and persistent enhancement. After a
brief post-contrast injection inhomogeneity has passed, most abnormalities
become readily evident and their conspicuity increases over time; barely
evident abnormalities on baseline scans are easily seen after contrast
injection.
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Top
Abstract
Introduction
