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Med Ultrason 2024:0, 1-7 Online rst
DOI:
Ahead of print
Comments on and illustrations of the WFUMB CEUS liver guidelines:
Rare malignant neuroendocrine and predominant epithelioid
liver lesions
Ehsan Safai Zadeh1, Katharina Paulina Huber2, Christian Görg3, Kathleen Möller4,
Christian Jenssen5, Adrian Lim6, Heike Taut7, Yi Dong8, Xin Wu Cui9, Christoph F Dietrich10
1Department of Biomedical Imaging and Image-Guided Therapy, Medical University of Vienna, Vienna, Austria,
2Department of General Internal Medicine and Psychosomatics, University Hospital Heidelberg, Germany,
3Interdisciplinary Center of Ultrasound Diagnostics, University Hospital Giessen and Marburg, Philipps University
Marburg, Marburg, Germany, 4Medical Department I/Gastroenterology; SANA Hospital Lichtenberg, Berlin,
Germany, 5Medical Department, Krankenhaus Maerkisch-Oderland, Brandenburg Institute of Clinical Medicine
at Medical University Brandenburg, Germany, 6Imperial College London and Healthcare NHS Trust, London, UK,
7Children’s Hospital, Universitätsklinikum Dresden, Technische Universität Dresden, Germany, 8Department of
Ultrasound, Xinhua Hospital Aliated to Shanghai Jiaotong University School of Medicine, Shanghai, China,
9Department of Medical Ultrasound, Tongji Hospital, Tongji Medical College, Huazhong University of Science and
Technology, Wuhan, China, 10Department Allgemeine Innere Medizin, Kliniken Hirslanden, Beau Site, Salem und
Permanence, Bern, Switzerland
Received 21.10.2023 Accepted 28.12.2023
Med Ultrason
2024:0 Online rst, 1-7
Corresponding author: Prof. Dr. med. Christoph F. Dietrich
Department Allgemeine Innere Medizin (DAIM)
Kliniken Beau Site, Salem und Permanence,
Hirslanden, Bern
CH-3036 Bern, Switzerland
Phone: +41 764408150
E-mail: c.f.dietrich@googlemail.com
Introduction
The guidelines for the utilization of contrast-en-
hanced ultrasound (CEUS) in the assessment of focal
liver lesions (FLLs) have been published by the World
Federation for Ultrasound in Medicine and Biology
(WFUMB) [1-5]. The primary focus of these guidelines
revolves around improving the detection and characteri-
zation of prevalent FLLs. Comprehensive descriptions
of both conventional ultrasound (US) including Doppler
techniques [6] and CEUS features pertaining to atypi-
cal FLLs have emerged. Existing literature, supported
by histological gold-standard, encompasses the study of
cholangiocellular adenoma [7], peliosis [8-10], heman-
gioendothelioma [11,12], and hepatocellular carcinoma
(HCC) in the non-cirrhotic liver. Numerous papers and
reports have been published on these rare and specialized
hepatic lesions. These encompass the characterization
of brolamellar hepatocellular carcinoma [13,14], very
small HCC (<10 mm) [15], mixed HCC and cholangio-
cellular carcinoma [16], nodular regenerative hyperpla-
sia [17], sarcoma [18], inammatory pseudotumour [19],
Abstract
The diagnosis or rare, non-hematologic malignant lesions of the liver may be a challenge owing to the rarity of the disease,
and is usually made by histological conrmation. Ultrasound with color Doppler and contrast-enhanced, if required, taking
into account the clinical background of the patient, may help to focus the dierential diagnosis. In this review, we describe the
pathological and ultrasound features of rare malignant neuroendocrine and predominantly epithelioid liver lesions including
primary neuroendocrine tumor of the liver, Invasive mucinous cystic neoplasm of the liver, and also hepatoblastoma.
Keywords: ultrasound; CEUS; primary neuroendocrine tumor; MCN-L; cystadenocarcinoma; hepatoblastoma
DOI: 10.11152/mu-4321
Comments on the WFUMB CEUS liver guidelines: Rare malignant
neuroendocrine liver lesions
2Ehsan Safai Zadeh et al Comments on the WFUMB CEUS liver guidelines: Rare malignant neuroendocrine liver lesions
sarcoidosis [20-23], tuberculosis [24, 25], hydatid cysts
[26-29], alveolar echinococcosis [27], schistosomiasis
[30,31], ascariasis [32,33], fasciolosis [34], clonorchis
and opisthorchis [35], toxocariasis [36], bacillary angio-
matosis [37], and amyloidosis with spontaneous hem-
orrhage [38], as well as rare FLLs in pediatric patients
[39,40]. More recently rare bacterial [41], parasitic [42],
and autoimmune focal liver lesions [43], bile duct lesions
[44], other benign FLL [45,46], and FLL other than HCC
in the cirrhotic liver [47,48] have been featured as well
[41-43,49].
Rare non-hematologic malignant hepatic lesions en-
compass those arising from mesenchymal origins, such
as diverse types of sarcoma, as well as those predomi-
nantly originating from non-mesenchymal tissue, includ-
ing primary neuroendocrine tumors, invasive mucinous
cystic neoplasm of the liver, and hepatoblastoma of the
liver. In this review, we describe the pathological and US
features of rare predominant non-mesenchymal lesions.
Nevertheless, it is imperative to highlight that the major-
ity of the description of tumor features on various im-
aging modalities have predominantly been derived from
isolated or limited case series.
Primary neuroendocrine tumor of the liver
Primary hepatic neuroendocrine tumors (PHNETs)
are very rare, accounting for approximately 0.46% of all
primary liver tumors [50]. Edmondson reported the rst
case of a PHNET in 1958 [51]. This condition is pre-
dominantly found in adults and is more common in the
right lobe of the liver, and it accounts for only 5% of
all neuroendocrine tumors [52]. PHNETs are commonly
found in people around the age of 50 years, with no gen-
der predominance. Most tumors are singular, but they can
also be multiple. Owing to the extremely slow growth of
PHNETs, obvious clinical symptoms are rare unless they
progress. Only a minority reveal the symptoms of classi-
cal carcinoid syndrome, such as skin ushing, diarrhea,
and abdominal pain [53]. In terms of the various imag-
ing features, it is always dicult to dierentiate PHNETs
from HCC or cholangiocarcinoma. Therefore, postopera-
tive histological and immunohistochemical evaluation
play an important role in diagnosing the disease. Further-
more, it is necessary to follow up with some patients for
an extended period to exclude other diagnoses. Common
pathological characteristics of primary neuroendocrine
tumors include gray-yellow, well-dened, and multiple
irregular hemorrhagic lesions or cystic areas. Through
the hematoxylin–eosin staining method, insular, nested,
trabecular, or mixed patterns of cell growth can be ob-
served [54]. Approximately 70% of the tumors can be
surgically removed, with a subsequent 5-year survival
rate in approximately 78% of patients. For inoperable
cases, various pharmacological treatments are available
to control the disease, including systemic 5-uorouracil,
hepatic artery embolization, and octreotide therapy [54,
55].
Cross-sectional imaging
On contrast-enhanced computed tomography, con-
trast enhancement is observed in the arterial phase, with
continuous enhancement into the venous phase [50]. The
tumor density on CT images may be lower than that of
the liver parenchyma. On Magnetic Resonance Imaging
(MRI) (g 1A,B), on T2-weighted and diusion-weight-
ed images, the PHNETs show a well-circumscribed, lob-
ular or multiple-nodular mass with high signal intensity.
Furthermore, the lesions are well-circumscribed, hetero-
geneous, and hypointense on T1-weighted images. Post
contrast T1-weighted images, show marked enhancement
of the solid tumor component in the early arterial phase,
persisting enhancement in the portal venous phase, and
high signal intensity or a clear defect in the 5-minute de-
layed hepatobiliary phase [56].
B-US and CEUS
On B-mode US, the lesions are visualized as hyper-
echoic (g 1C) (60%) or mixed echoic (30%), inhomo-
geneous, and sometimes with cystic components [57].
The lesions may have a similar pattern to that of heman-
giomas. However, in contrast to hemangiomas, vessels
are detected in the lesions on color Doppler US (g 1D).
On CEUS, lesions commonly show marked arterial en-
hancement followed by washout in the portal and/or late
phases (g 1E-H) [58-60].
Invasive mucinous cystic neoplasm of the liver
Mucinous cystic neoplasm of the liver (MCN-L)
and invasive mucinous cystic neoplasm of the liver (I-
MCN-L) are extremely rare tumors of the liver. To date,
less than 200 cases have been described in the literature
[61,62]. They originate from the bile duct epithelium
and are usually multilocular. These neoplasms present as
solitary hepatic lesions consisting of multiple cysts with
varying contents and surrounded by a thick capsule [62].
I-MCN-L (previously known as cystadenocarcinomas)
are rare, with an incidence of 0.41% of all hepatic malig-
nant epithelial tumors [62,63]. However, a high risk of up
to 20% of malignant transformation has been described
for MCN-L (previously known as biliary cystadenomas)
[64]. Furthermore, the nding of benign areas in cystad-
enocarcinomas histologically, have led to the hypothesis
that I-MCN-L develop via malignant transformation
from MCN-L [62].
3
Med Ultrason 2024; 0: 1-7
These tumors grow very slowly and can reach enor-
mous dimensions before they are symptomatic. They
frequently cause only non-specic abdominal symptoms,
thus the diagnosis remains dicult despite the broad va-
riety of imaging techniques available [62]. In some cases
of cystadenomas as well as cystadenocarcinomas, tumor
markers such as AFP, CEA, CA 125, or CA 19-9 may be
elevated in serum or intracystic tissue. However, dier-
entiation between benign and malignant cystadenomas is
not possible using tumor markers alone [62,64]. Benign
histology obtained by needle biopsy cannot exclude ma-
lignancy of the lesions because, in cystadenocarcinomas,
benign and malignant tumor areas are often located side
by side [62]. Currently, radical tumor resection with a
negative margin is considered the treatment of choice,
not only for malignant, but also benign cystadenomas of
the liver, because it is not possible to distinguish between
MCN-L and I-MCN-L radiologically or macroscopically.
In addition, the high malignant transformation rate of
MCN-L should be taken into account [62,64]. For pa-
tients with an inoperable or advanced tumor stage, radio-
therapy and chemotherapy can be considered [65].
Cross-sectional imaging
A reliable dierentiation between benign and malig-
nant cystic hepatobiliary lesions is not possible based on
current imaging modalities. In the diagnosis of biliary
cystic liver tumors, the roles of US and CT have been
described as complementary [62,64].
On CT (g 2A), these tumors appear hypodense and
show irregularly thickened walls, internal septa, and mu-
cosal nodules. Individual areas may show dierent densi-
ty values, and these are probably due to dierent concen-
trations of mucinous, serous, or partly hemorrhagic uid
[62]. Compared with US, CT provides a better overview
and therefore better assessment of size, extension, and
anatomic relationships with neighboring organs [62]. On
contrast-enhanced CT, contrast enhancement is observed
in the area of the septa and walls, and this is similar to
that of the liver parenchyma. Intramural or septal calci-
cations may also be detectable [62].
On MRI (g 2B), cysts present as homogeneous low
intensity on T1-weighted images compared with the nor-
mal liver parenchyma. On T2-weighted images, they
show high-intensity signal, similar to uid-lled cavities
and can be clearly demarcated from the normal liver tis-
sue [62]. MRI is considered complementary to US and
CT for the preoperative diagnosis of these tumors and the
accurate assessment of the anatomical relationship of the
tumor with neighboring organs [62,64].
B-US and CEUS
US is considered the method of choice in the pre-
operative diagnosis of hepatobiliary cystic tumors. The
Fig 1. A 40-year-old female patient with non-specic abdominal pain and a sonographically detected hyperechoic hepatic lesion.
Visualization of the lesion on magnetic resonance imaging (courtesy of Prof. Dr. Mahnken, Department of Radiology, University
Hospital Marburg) (A), positron emission tomography computed tomography (courtesy of Prof. Dr. Luster, Department of Nuclear
Medicine, University Hospital Marburg) (B), and B-mode ultrasound (C). On color Doppler sonography, vessels are detectable in
the lesion (D). On contrast-enhanced ultrasound, the lesion shows hyperenhancement after 23 s (E), with increasing hypoenhance-
ment after 3 min (F), 5 min (G), and 7 min (H). An ultrasound-guided biopsy was performed, and the diagnosis of well-dierentiated
primary hepatic neuroendocrine tumor (G1, Ki67: 0.5%) was conrmed histologically.
4Ehsan Safai Zadeh et al Comments on the WFUMB CEUS liver guidelines: Rare malignant neuroendocrine liver lesions
lesions present as oval or roundish cystic masses with
multiple septa (g 2C). These may vary in number and
thickness. Wall irregularities and nodular, papillary
mucosal changes can also be seen on US and are rela-
tively typical of cystadenomas and cystadenocarcinomas
[62,64]. On CEUS, the septa and wall irregularities may
demonstrate contrast enhancement (g 2E, F).
Hepatoblastoma
Hepatoblastoma incidence rates are approximately
10.5 and 5.2 cases per million children under 1 year and
between 1 to 4 years, respectively. Beyond these age
ranges, the occurrence of hepatoblastoma are insucient
to establish a reliable incidence rate [66]. However, hepa-
toblastoma accounts for approximately 90% of hepatic
malignancies in children aged below 5 years and is the
most common type of liver malignancy in this age group
[67,68]. Hepatoblastomas can be classied into two
main subtypes: the more frequent epithelial type, and the
mixed type, which is characterized by a combination of
epithelial and mesenchymal components [69]. The mixed
type accounts for approximately 20-30% of all hepato-
blastoma tumors and exhibits a variable combination of
the two components [69]. The main symptoms associated
with hepatoblastoma include abdominal distension and
Fig 3. A 1-year-old male boy with a slightly hyperechoic liver lesion with accompanying satellite lesion (green arrow) and detect-
able intralesional vessels on CDS (A). On contrast enhanced ultrasound (B), after 2 minutes, the largest lesion (green arrow) shows
marked wash-out. Furthermore, multiple satellite lesions are demarcated (white arrows).
Fig 2. A 57-year-old female patient with a polycystic liver space lesion and upper abdominal pain. Visualization of the lesion on com-
puted tomography (courtesy of Prof. Dr. Mahnken, Department of Radiology, University Hospital Marburg) (A), magnetic resonance
imaging (B), and B-mode ultrasound (C, D). On contrast-enhanced ultrasound, the lesion shows marked enhancement after 30 s
(E) and 1 min (F). Histologically, a diagnosis of mucinous cystic neoplasia (hepatobiliary cystadenoma) was conrmed, followed by
tumor resection in accordance with the tumor board’s decision.
5
Med Ultrason 2024; 0: 1-7
weight loss [68,70]. Typically, hepatoblastoma presents
as a large solid mass with multiple compartments, vary-
ing in size, and may exhibit pseudocystic areas, necrosis,
and calcications. The diagnosis is aided by a signicant
increase in alpha-fetoprotein levels. CT and MRI are the
primary methods used for oncological staging [68,71].
The specic role of CEUS in hepatoblastoma, particu-
larly in follow-up examinations, has not been clearly de-
ned [68].
Cross-sectional imaging
On CT, hepatoblastoma is typically visualized as a
well-dened heterogeneous mass, which generally ap-
pears hypoattenuating in comparison to the surrounding
liver [72]. There are often occurrences of necrotic and
hemorrhagic areas. Calcication may be present [72]. On
MRI, a typical hepatoblastoma presents as a tumor with
heterogeneously increased signal intensity on T2-weight-
ed images, decreased signal intensity on T1-weighted
imaging, and shows heterogeneous enhancement pat-
terns during contrast administration. However, the tumor
remains predominantly hypointense compared to the sur-
rounding liver tissue throughout all phases of contrast
enhancement. Additionally, calcications may be present
within the tumor mass, and variable incidences of hemor-
rhage and necrosis contribute to the heterogeneous pat-
terns [73].
B-US and CEUS
On B-US, hepatoblastomas exhibit heterogeneity and
variable echogenicity. Hepatoblastoma can present as a
solitary dominant mass with accompanying satellite le-
sions, multiple nodules distributed throughout the liver,
or rarely, as a diusely inltrative mass aecting the en-
tire liver [74]. Calcications may be observed [74]. In-
ternal hemorrhage and necrosis are relatively common.
Color Doppler US is a valuable modality for identifying
potential invasion of the hepatic and portal veins [74].
On CEUS, the special features of hepatoblastoma include
initial peripheral hyperenhancement during the arterial
phase and pronounced wash-out in the subsequent late
portal venous phase (g 3, g 4) [75].
Conclusion
Similar to common liver tumors, the diagnosis of the
previously mentioned tumors should be made taking into
account the clinical background of patients. Primary neu-
roendocrine tumors of the liver may mimic the appear-
ance of a hemangioma on B-US. On CEUS, the wash-
out may appear late owing to marked neoangiogenesis.
Therefore, the lesion should be observed for at least 5
minutes. Hepatoblastomas are characterized by hyper-
enhancement and a marked wash-out phenomenon. Any
cyst with enhancement of the septa or irregular walls on
CEUS should be considered as a potential I-MCN-L re-
quiring further evaluation.
Conict of interest: none
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