Exophytic Benign and Malignant Hepatic Tumors: CT Imaging Features

Abstract

Our objective is to describe the CT features of exophytic hepatic tumors those may pose a diagnostic challenge because of the uncertainty of tumor origin. The beak sign and the feeding artery of a tumor are useful diagnostic indicators of exophytic hepatic tumors. Two- or three-dimensional reformation images are also helpful for diagnosis. The CT features of exophytic hepatic tumors are similar to those of the usual intrahepatic tumors except for their location.

Full text

Korean J Radiol 9(1), February 2008 67
Exophytic Benign and Malignant Hepatic
Tumors: CT Imaging Features
Our objective is to describe the CT features of exophytic hepatic tumors those
may pose a diagnostic challenge because of the uncertainty of tumor origin. The
beak sign and the feeding artery of a tumor are useful diagnostic indicators of
exophytic hepatic tumors. Two- or three-dimensional reformation images are also
helpful for diagnosis. The CT features of exophytic hepatic tumors are similar to
those of the usual intrahepatic tumors except for their location.
f the center of a tumor lies beyond the confines of the liver and the tumor
originates from the liver, it can be defined as an exophytic hepatic tumor
(1). Benign tumors such as a hepatic cyst, hemangioma, hepatic adenoma,
focal nodular hyperplasia, and angiomyolipoma and malignant tumors such as a
hepatocellular carcinoma, cholangiocellular carcinoma, and metastases may show
exophytic growth. Although the use of CT can demonstrate the presence of the tumor
itself, making a correct diagnosis is often challenging for radiologists because of the
uncertainty of the tumor origin.
In the diagnosis of exophytic hepatic tumors, the first step is to determine whether
the tumor has originated from the liver. The ‘beak sign’ and the ‘prominent feeding
artery sign’ are useful for identifying the origin of the tumor (2). Two- or three-
dimensional reformation images are also helpful. The second step is to recognize the
specific imaging features of a tumor such as the dynamic enhancement pattern, fatty
component, homogeneity, etc. The aim of this pictorial essay is to show the CT
features of various exophytic hepatic tumors.
Benign Exophytic Hepatic Tumors
Hepatic Cyst
Most of the hepatic cysts identified on CT can be diagnosed with confidence. The CT
features of simple hepatic cysts are a well-defined intrahepatic lesion, water attenua-
tion, round shape, thin wall, no septation, absence of internal structure, and no
enhancement after administration of contrast material (3). If a hepatic cyst
demonstrates exophytic growth, it may be misinterpreted as a pancreatic (Fig. 1) or
omental cystic mass (Fig. 2). If a cyst is seen adjacent to the liver, the possibility of
exophytic hepatic cyst should be considered and careful evaluation of the coronal and
sagittal reformation images is mandatory.
Hemangioma
The majority of hepatic hemangiomas identified on CT can be diagnosed accurately
Hyoung Jung Kim, MD1
Dong Ho Lee, MD1
Joo Won Lim, MD1
Young Tae Ko, MD1
Kyoung Won Kim, MD2
Index terms:
Computed tomography (CT)
Liver
Neoplasm
DOI:10.3348/kjr.2008.9.1.67
Korean J Radiol 2008;9:67-75
Received January 18, 2007; accepted
after revision April 25, 2007.
1Department of Radiology, Kyung Hee
University Medical Center, Seoul 130-
702, Korea; 2Department of Radiology,
University of Ulsan College of Medicine
and Asan Medical Center, Seoul 138-736,
Korea
Address reprint requests to:
Hyoung Jung Kim, MD, Department of
Radiology, Kyung Hee University Medical
Center, 1, Hoegi-dong, Dongdaemun-gu,
Seoul 130-702, Korea.
Tel. (822) 958-8621
Fax. (822) 968-0787
e-mail: radhjkim@khu.ac.kr
I

by CT examinations alone from the characteristic imaging
features of these lesions. On hepatic artery phase dynamic
CT, they show peripheral nodular or globular enhance-
ment (4). With time, contrast enhancement progresses
centripetally (4). The reported incidence of exophytic
hemangiomas was about 12% in cirrhotic patients (5).
However, pedunculated hemangiomas are very rare (6).
Pedunculated hemangiomas can be asymptomatic or can
be complicated by torsion and infarction. Pedunculated
exophytic hemangiomas may show a thin pedicle that
contains a feeding artery and draining vein, and this
pedicle connects the hemangioma to the liver (Fig. 3).
Other usual exophytic hemangiomas just show the beak
sign (Fig. 4).
Hepatocellular Adenoma
A hepatocellular adenoma is a rare benign tumor that is
usually encountered in young women that use oral contra-
ceptives. Macroscopically, a hepatocellular adenoma is a
spherical, sometimes pedunculated, well demarcated, often
encapsulated solitary liver tumor (7). Exophytic growth or
distortion of the hepatic contour was present in 25% of
cases (8). Angiographically, a hepatocellular adenoma
presents as a hypervascular mass with centripetal flow (9).
On non-enhanced and enhanced CT images, adenomas are
usually heterogeneous because of fatty infiltration,
hemorrhage, and necrosis (7). Therefore, identification of
the feeding artery and the heterogeneous attenuation on
CT may provide clues for the diagnosis of an exophytic
hepatic adenoma (Fig. 5).
Focal Nodular Hyperplasia
Focal nodular hyperplasia is the second most common
benign neoplasm of the liver. It is more common in women
and it is seen predominantly during the third and fifth
decades of life. Grossly, a focal nodular hyperplasia is a
well-circumscribed, solitary mass that is often located on
the surface of the liver or is pedunculated (10). In one
study, a subcapsular location was seen in 81% of cases and
exophytic growth or distortion of the hepatic contour was
seen in 32% of the cases (10). On dynamic CT, the lesion
enhances brightly and homogeneous on hepatic arterial
Kim et al.
68 Korean J Radiol 9(1), February 2008
AB
Fig. 1. A 64-year-old woman with an exophytic hepatic cyst.
A. A contrast-enhanced CT scan shows a well-defined, cystic
mass (arrow) in the pancreas. Mural nodule or septation is not
noted. The lesion was initially interpreted as a mucinous cystic
neoplasm of the pancreas.
B. A photograph taken during surgery shows a cyst (arrow) arising
from the caudate lobe.
C. A sagittal reformation image shows a cyst with beak sign (arrow)
in its contact surface with the caudate lobe; however, this cyst
shows a dull edge (arrowhead) in its contact surface with the
pancreas.
C

Exophytic Benign and Malignant Hepatic Tumors
Korean J Radiol 9(1), February 2008 69
AB
Fig. 2. A 72-year-old woman with an exophytic hepatic cyst.
A. A contrast-enhanced CT scan shows a well-defined, cystic
mass (arrow) adjacent to the greater curvature side of the
stomach. Initially, the lesion was interpreted as an omental cyst,
lymphangioma, or duplication cyst. Thin band-like opacity
(arrowhead) is suspicious at the anteromedial aspect of the cystic
mass.
B. A photograph taken during surgery shows a thin stalk (arrow)
that connects the cyst with the lateral segment, crossing over the
stomach (S).
C. A coronal reformation image shows a thin stalk (arrow) connect-
ing the cyst with the lateral segment.
C
Fig. 3. A 53-year-old woman with a pedunculated hemangioma.
A. A contrast-enhanced CT scan during hepatic arterial phase shows a small nodular lesion (arrow) adjacent to the greater curvature
side of the stomach. There is a vascular pedicle (arrowheads) connecting nodule with the lateral segment (prominent feeding artery
sign). It shows dense peripheral enhancement.
B. A contrast-enhanced CT scan during portal venous phase shows centripetal enhancement of this small nodule (arrow).
AB

Kim et al.
70 Korean J Radiol 9(1), February 2008
Fig. 4. A 51-year-old woman with an exophytic hemangioma.
A, B. Contrast-enhanced CT scans show a large low density mass in the lesser sac. The beak sign is seen in its contact surface with the
caudate lobe (arrow in A) and dense peripheral globular enhancement (arrowheads) is noted. A Tc-99m RBC scan (not shown) shows a
blood pooling mass in the same location as on the CT image.
AB
AB
Fig. 5. A 23-year-old woman with an exophytic hepatocelluar
adenoma.
A. A contrast-enhanced CT scan during hepatic arterial phase
shows a heterogeneous and mild high-density mass (arrows),
below the right lobe. Prominent subcapsular vessels are noted
(arrowhead). The beak sign is not definite on serial axial images
(not shown).
B. On a contrast-enhanced CT scan during portal venous phase,
the mass (arrows) shows persistent heterogeneity and a slightly
decreased density.
C. An oblique coronal maximum-intensity-projection image during
hepatic arterial phase shows a large branch (arrowhead) from the
right hepatic artery supplying this mass (arrows).
C

phase, and it enhances similar to that of normal liver on
portal venous phase and delayed phase images (10).
Therefore, identification of the feeding artery, the
homogeneity except for the central scar, and strong
enhancement during hepatic arterial phase on CT images
may provide clues for the diagnosis of an exophytic focal
nodular hyperplasia (Fig. 6).
Angiomyolipoma
Hepatic angiomyolipomas are usually solitary and
predominantly seen in women. Histologically, they are
composed of smooth muscle, fat, and vessels in various
combinations. As far as we know, there is only one report
describing a pedunculated or exophytic angiomyolipoma
arising from the liver (11). Angiographically, angiomy-
olipomas are hypervascular and they may show aneurysms
(12). Angiomyolipomas can have various CT appearances
because of the variable fatty component that ranges
between 5% and 90% (13). Identification of the feeding
artery arising from the liver and the fatty component of
the mass on CT may provide clues for the diagnosis of an
exophytic angiomyolipoma (Fig. 7).
Exophytic Benign and Malignant Hepatic Tumors
Korean J Radiol 9(1), February 2008 71
AB
Fig. 6. A 26-year-old man with an exophytic focal nodular hyperplasia.
A. A contrast-enhanced CT scan during hepatic arterial phase shows a homogeneous
high-density mass (arrow) in the left lobe. The feeding artery (arrowhead) is noted in
the central portion of the mass.
B. On a coronal reformation image during the portal venous phase, the beak sign is
noted in its contact surface with the lateral segment (arrow).
C. An oblique coronal volume rendering image during hepatic arterial phase shows a
prominent left hepatic artery (arrow) and a small central artery (arrowhead) supplying
this mass.
D. A pathological specimen shows the beak sign (arrow) in its contact surface with the
lateral segment and a small central artery (arrowhead) within the fibrous scar.
C
D

Kim et al.
72 Korean J Radiol 9(1), February 2008
AB
Fig. 7. A 52-year-old woman with an exophytic angiomyolipoma.
A. A contrast-enhanced CT scan during hepatic arterial phase
shows a fatty mass in the lateral segment of the liver. This fatty
mass shows the beak sign (arrow) in its contact surface with the
lateral segment. The left hepatic artery (arrowhead) is enlarged
and it is a prominent feeding artery supplying this fatty mass.
B. On a contrast-enhanced CT scan during portal venous phase, 4
cm below (A), most of the huge fatty mass (arrows) is located in
the peritoneal cavity.
C. Hepatic arteriography shows a dilated left hepatic artery (arrow)
and prominent tumor vessels.
C
Fig. 8. A 57-year-old woman with an exophytic hepatocellular carcinoma with duodenal invasion.
A. A contrast-enhanced CT scan during hepatic arterial phase shows a large necrotic mass, compressing the lateral wall of the
duodenum (D). The solid portion of this mass (arrow) shows iso-density in comparison with the liver parenchyma.
B. On a contrast-enhanced CT scan during portal venous phase, the solid portion of this mass (arrow) shows low density in comparison
with the liver parenchyma. The beak sign (arrowhead) is noted in its contact surface with the right lobe. The fine nodular hepatic surface
suggests liver cirrhosis. The lateral wall of the duodenum (D) is not definite.
AB

Malignant Exophytic Hepatic Tumors
Hepatocellular Carcinoma
Hepatocellular carcinoma (HCC) is the most common
primary malignant hepatic tumor. Exophytic growth or
pedunculation is not a novel finding of HCCs. It has been
reported that exophytic HCCs constitute 0.2 4.2% of all
HCCs (14, 15). It is well known that HCC may show
retroperitoneal extension and thus mimic a right adrenal
tumor (16). However, exophytic growth of HCCs may be
seen in any lobe or segment of the liver. This tumor may
invade the duodenum and mimic a duodenal gastrointesti-
nal stromal tumor (Fig. 8). Bile duct and portal vein
invasion are late presentations in usual intrahepatic HCCs
and they may be seen in exophytic HCCs. Most intraductal
masses are contiguous with the parenchymal HCCs (17).
Therefore, an exophytic hepatic mass contiguous with a
bile duct mass is a similar finding to a usual intrahepatic
HCC with bile duct invasion, except for location (Fig. 9).
On dynamic CT, an intraductal HCC shows high density
during hepatic arterial phase and washout during portal
venous phase. Therefore, typical enhancement pattern of
HCC, surrounding cirrhotic liver, and bile duct dilatation
by the mass may be clues for the diagnosis of an exophytic
HCC.
Mass-forming Intrahepatic Cholangiocarcinoma
A mass-forming intrahepatic cholangiocarcinoma
(peripheral cholangiocarcinoma) arises from the intrahep-
atic bile duct epithelium and grows into a focal mass.
Grossly, this neoplasm consists of a peripheral zone of
neoplastic cells without fibrosis and a fibrosed central zone
due to a desmoplastic reaction provoked by the neoplastic
cells (18). On dynamic CT, minimal to moderate peripheral
enhancement is followed by progressive and concentric
Exophytic Benign and Malignant Hepatic Tumors
Korean J Radiol 9(1), February 2008 73
A
C
Fig. 9. A 57-year-old man with an exophytic hepatocellular
carcinoma and bile duct invasion.
A. A contrast-enhanced CT scan during hepatic arterial phase
shows a small high-density mass (arrow) posterior to the lateral
segment. Dense tubular enhancement (arrowhead) in the lateral
segment shows a connection with this small mass.
B. On a contrast-enhanced CT scan during portal venous phase,
the small mass (arrow) and tubular lesion (arrowhead) shows low
density in comparison with liver parenchyma. A fine nodular
hepatic surface and hypertrophied lateral segment suggest liver
cirrhosis.
C. On endoscopic retrograde cholangiography, there is a filling
defect (arrow) in the B2 duct, which was seen as a tubular high
density on hepatic arterial phase image (A). On surgery, it was
confirmed as an exophytic hepatocellular carcinoma and bile duct
invasion.
B

filling of the tumor with contrast material (19). Any
prominent feeding artery or draining vein is not noted in
an exophytic cholangiocellular carcinoma, as this tumor is
not highly vascularized. Therefore, its typical enhancement
pattern, the surrounding non-cirrhotic liver, and the beak
sign may be clues to reaching a correct diagnosis (Fig. 10).
Metastasis
Metastases are by far the most common malignant
tumors of the liver. The CT appearance depends on the
tumor size, the vascularity, and the degree of hemorrhage
and necrosis. Although a single metastasis or oligonodular
involvement may be seen, multiple metastatic lesions are
the general rule. If one considers that various benign and
malignant hepatic tumors may show exophytic growth, it is
not surprising that a metastasis may show exophytic
growth. Multiplicity and a known or suspicious primary
site are the keys to reach a correct diagnosis (Fig. 11).
CONCLUSION
Various benign and malignant hepatic tumors may show
exophytic growth. The CT features of exophytic hepatic
tumors are similar to those of their intrahepatic counter-
parts. If the tumors adjacent to the liver show CT features
that are typical for hepatic neoplasms, then the exophytic
hepatic tumors should be considered in a differential
diagnosis and attention should be given to the clues
implying a hepatic origin before making a final diagnosis.
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