Dr. Anderson and Dr. Soto are at the Department of Radiology, Boston University Medical Center, Boston, MA. Dr. Kruskal is at Department of Radiology,Beth Israel Deaconess Medical Center, Boston, MA.
liver tumors are exceedingly common and frequently encountered in daily
clinical practice. And while their typical appearances pose no
significant diagnostic challenge, the atypical appearances may pose
difficulty, given their unfamiliarity to many radiologists. Also, an
overlap in imaging characteristics in some cases may preclude the
definitive differentiation between benign tumors or the confident
exclusion of more ominous, malignant lesions. Therefore, understanding
the common and uncommon appearances of frequently encountered benign
liver tumors as well as the expected appearance of rarely seen tumors is
important. Strategies for confidently diagnosing liver tumors or, in
some cases, concluding that additional imaging or an invasive procedure
is warranted, are equally vital.
While various methods of
categorizing benign liver tumors are possible, a classification based on
their cell of origin offers an intuitive,simple approach. Thus, we will
consider benign liver tumors of epithelial and nonepithelial origin,
with the epithelial tumors further classified into tumors of either
cholangiocellular or hepatocellular origin. Of the nonepithelial tumors,
those of mesenchymal cell origin will be considered.
Benign hepatic tumors of cholangiocellular origin
cysts are extremely common, identified on imaging in > 10% to 15% of
the population, and their isolated, simple appearance typically poses
no diagnostic difficulty.1 Simple hepatic cysts are
epithelial lined; the epithelium is similar to that of the bile ducts.
While their etiology has not been definitively established, isolated
hepatic cysts are hypothesized to be hamartomatous tissue.2 Simple hepatic cysts are typically incidentally discovered, with rare complications including infection and cyst rupture.3
cysts are also associated with polycystic liver diseases, which consist
of a heterogeneous group of disorders of biliary epithelium,including
autosomal-dominant polycystic kidney disease, isolated polycystic liver
disease, and the fibropolycystic liver diseases.4 Patients
with autosomal-dominant polycystic kidney disease (ADPKD) demonstrate
multiple cysts in the kidney, liver, and pancreas, and while their liver
is often enlarged with numerous cysts, function tends to be preserved.
Isolated polycystic liver disease, which is far less common thanADPKD,
is characterized by numerous hepatic cysts and an absence of renal
cysts. Finally, the fibropolycystic liver diseases include various
disorders, including congenital hepatic fibrosis, Caroli disease,
autosomal recessive polycystic kidney disease (ARPKD), and biliary
hamartoma. Of the fibropolycystic liver diseases, patients with
congenital hepatic fibrosis and Caroli disease often develop recurrent
acute cholangitis and portal hypertension secondary to peribiliary
fibrosis (Figure 1). In addition, Caroli disease patients are at
increased risk for developing cholangiocarcinoma (Figure 1).5 Biliary
hamartomas, also referred to as von Meyenburg complex, are common,
benign lesions characterized by the presence of numerous, small cystic
lesions in the liver parenchyma ranging from 2 mm to 15 mm (Figure 2).6 On
both computed tomography(CT) and magnetic resonance imaging (MRI),
biliary hamartomas are characterized as small cystic lesions, the cystic
nature of which may be more readily apparent on MRI; in some cases,
uniform or peripheral enhancement of these lesions has been reported.7
Biliary cystadenomas are rare, typically multilocular neoplasms of the bile ducts that are more frequently encountered in women.2 These
predominantly cystic tumors frequently consist of proteinaceous fluid,
and a thick capsule, internal septations, and areas of calcification
maybe identified on imaging.8 In addition, nodular, enhancing
soft-tissue components may be identified within these lesions, but do
not definitively indicate the presence of a malignant
cystadenocarcinoma. Given the significant overlap of imaging findings
between biliary cystadenomas and malignant biliary cystadenocarcinomas,
which precludes definitive differentiation, surgical consultation is
Intraductal papillary neoplasm of the bile ducts
papillary neoplasm (IPN) of the bile ducts encompasses a range of
clinical and histologic features and is characterized by the presence of
intraluminal tumors of the bile ducts, which often produce mucobilia as
a distinctive feature (Figure 3).9 This entity parallels the
more commonly encountered and familiar intraductal papillary mucinous
neoplasm (IPMN) of the pancreas, in that the tumors range from benign to
malignant, and are classified as adenoma, borderline tumor, carcinoma
in situ, or carcinoma, though most cases are reportedly at least
carcinoma in situ, a distinction from IPMN of the pancreas. On imaging,
biliary dilatation is often present, related to the mucobilia, which is
associated with this disease process, is often present on imaging. In
addition, cystic intrahepatic mass lesions may be identified; in some
cases, direct communication with adjacent intrahepatic bile ducts may
also be identified on imaging.9
cysts represent retention cysts of peribiliary glands, identified along
the course of the portal veins, predominantly in the centralliver.10 Peribiliary
cysts are associated with advanced and portal hypertensive liver
disease and are also present in patients with polycysticliver disease.11 Uncommon
complications of peribiliary cysts include obstructive jaundice and
hepatolithiasis. On imaging, peribiliary cysts may be misinterpreted as
intrahepatic biliary dilatation, given their cystic nature and their
presence along the bile ducts. Their central location as well as the
direct visualization of their discrete cystic nature, which is typically
apparent on MRI, offers useful imaging features in differentiating
peribiliary cysts from biliary dilatation.
Intrahepatic bile duct adenoma
bile duct adenomas are rare, benign tumors composed of disorganized but
mature peribiliary gland acini and tubules. The etiology of these
lesions remains uncertain, but they are thought to represent bile
ductular reaction to a focal insult. On imaging, the lesions have been
reported to be located in the periphery of the liver and to demonstrate
early peripheral as well as delayed, persistent enhancement after
contrast administration (Figure 4).12 On MRI, relative hypointensity on both T1- and T2-weighted images has been reported (Figure 4).13
Benign hepatic tumors of hepatocellular origin
Focal nodular hyperplasia
Focal nodular hyperplasia (FNH) represents the second-most common benign tumor of the liver with a reported incidence of 0.9%.14 Typically
an incidental finding on imaging studies, FNH is theorized to represent
a hyperplastic response to a localized vascular abnormality, given its
association with benign vascular neoplasms, including hemangiomas. The
differentiation of FNH from other hepatocellular lesions, such as
hepatic adenoma and hepatocellular carcinoma, is clinically important
and may be confidently achieved with noninvasive imaging.
prominent central scar is identified, FNH is often subtle on
ultrasound, with only minimal differences in echogenicity compared to
the normal liver parenchyma. On contrast CT, FNH is characterized by
brisk, homogeneous enhancement, save for the central scar (Figure 5). On
subsequent, later phases of enhancement, the lesions typically become
increasingly isoattenuating with respect to the adjacent liver
parenchyma while the central scar may demonstrate enhancement,
particularly on a more delayed phase of image acquisition. The presence
of a central scar, a useful imaging feature in the confident diagnosis
of FNH, has been reported in 50% of cases withCT imaging.15 Similar
enhancement characteristics, including the central scar, have been
reported on MRI. Compared to ultrasound and CT,MRI has both a higher
sensitivity and specificity for FNH and detects the central scar more
frequently.16 In cases in which a central scar is not readily
identified or typical imaging features are not present, hepatocellular
contrast agents may improve confidence in differentiatingFNH from other
hepatocellular lesions (Figure 5). In the case of gadobenate
dimeglumine, 97% of FNH are reported to be hyper- or isointense with
respect to the adjacent liver parenchyma on the hepatocellular phase of
image acquisition.17 In the case of gadoxetic acid, 100%
ofFNH has been reported to be hyperintense with respect to the adjacent
liver parenchyma on the hepatocellular phase of image acquisition.18 These
contrast agents may increase reader confidence in the diagnosis or
exclusion of FNH based on differences in enhancement patterns between
this tumor and other hepatocellular lesions, discussed below.
adenomas are rare, benign liver tumors that are almost exclusively
identified in young women taking oral contraceptives. In addition to
estrogen-containing oral contraceptives, androgen-containing steroids
and type I glycogen storage disease have been associated with hepatic
adenomas.19 While typically solitary, multiple adenomas may
be present; when > 10 adenomas are present, this is referred to as
liver adenomatosis. Hepatic adenomas consist of hepatocytes arranged in
sheets and cords instead of the typical lobular architecture, and they
also include dilated sinusoids fed by prominent arteries.20 Feared
complications of hepatic adenomas include a risk of hemorrhage, given
the aforementioned tumoral architecture, as well malignant degeneration,
and, therefore, their accurate diagnosis is of significant clinical
On ultrasound, hepatic adenomas are
often echogenic with respect to the adjacent liver parenchyma, a finding
that may reflect intratumorallipid or hemorrhage. Hemorrhage may also
result in an increase in heterogeneity of the tumors on ultrasound.19 Intratumoral
fat and hemorrhagemay be readily identified on CT, especially on
unenhanced images. On contrast images, heterogeneous arterial
enhancement is often identified,reportedly less marked compared to the
brisk enhancement seen in FNH. On MRI, intratumoral fat may be readily
assessed using chemical shift imaging, present in the overwhelming
majority of cases in certain subtypes of hepatic adenoma assessed by
MRI.21 Hepatic adenomas have mixed appearances on T1-weighted
images, but they may be hyperintense secondary to the presence of
hemorrhage or fat. On T2-weighted images, most hepatic adenomas are
hyperintense with respect to the adjacent liver parenchyma (Figure 6).19 On
contrast MR images, enhancement patterns similar to those described on
CT are expected. The use of hepatocellular contrast agents offers
additional data that may diagnose or exclude hepatic adenomas. With
gadobenate dimeglumine, 100% of hepatic adenomas are reported to be
hypointense with respect to the adjacent liver on the hepatocellular
phase of image acquisition.17 However, with gadoxetic acid,
hepatic adenomas have been reported to be hyperintensewith respect to
the adjacent liver on the hepatocellular phase of image acquisition,
which yields overlapping imaging features with FNH and precludes
definitive differentiation in these cases.18,22 However, in
cases in which hepatic adenomas are hyperintense with respect to the
adjacent liver on the hepatocellular phase of image acquisition, the
degree of hyperintensity has been reported to be useful in
differentiating hepatic adenoma from FNH.22
Benign hepatic tumors of mesenchymal origin
hemangiomas are the most common solid, benign liver tumor; they consist
of blood-filled spaces lined by endothelium, along with a variable
presence of thrombi, calcification, fibrosis, and scarring. On
unenhanced CT, relative hypoattenuation of hemangiomas are the expected
appearance, though this may vary with the state of the surrounding liver
parenchyma. For instance, in cases of significant hepatic steatosis,
hepatic hemangiomas may be relatively hyperattenuating with respect to
the adjacent, abnormally hypoattenuating liver parenchyma (Figure 7). On
MRI, marked T2 hyperintensity is a useful, specific imaging feature of
hepatic hemangiomas (Figure 8). On contrast imaging (CT as well as MRI),
3 general enhancement patterns may be expected, which somewhat depend
on lesion size. In small hemangiomas, immediate uniform enhancement, so
called “flash-filling,” may be observed.23 The most common
pattern consists of a peripheral nodular enhancement that progresses
centripetally over time to uniform enhancement on more delayed phases of
image acquisition. Finally, especially in larger hemangiomas and giant
hemangiomas (defined as having a diameter exceeding 5 cm), the early
peripheralnodular enhancement may progress centripetally, but a
persistent lack of uniform enhancement is seen on the more delayed
phases of image acquisition.23 Additional atypical imaging
features of hepatic hemangiomas include calcifications, a multilocular
appearance, fluid-fluidlevels, hyalinization—which results in less
marked T2 hyperintensity and a reduction in the degree of
enhancement—and a pedunculated morphology, among others (Figure 8).23 The
presence of hepatic hemangiomas is less common in cirrhotic livers;
this is thought to be related to obliteration secondary to fibrosis.
While hemangiomas in cirrhotic livers may pose a diagnostic dilemma
given the increased incidence of hepatocellular carcinoma in this
patient population, the expected imaging features of hemangiomas are
typically present, allowing for confident diagnosis of this benign
Benign, macroscopic fat-containing liver lesions of mesenchymal origin include hepatic angiomyolipomas and hepatic lipomas.25
Hepatic angiomyolipoma (AML) is a benign mesenchymal tumor composed of
mature adipose tissue, thick-walled vessels, and smooth muscle. Any
single component may dominate, and the relative composition of
angiomyolipomas strongly dictates the imaging appearance.Compared to
renal angiomyolipomas, there is a lesser degree of association between
hepatic angiomyolipomas and tuberous sclerosis.26 Similar to
renal angiomyolipomas, complications of hepatic AMLs include hemorrhage.
The macroscopic fat hepatic AMLs may be readily identified on CT as
well as on MRI with fat-suppression techniques, and brisk enhancement of
the hepatic AMLs is often observed on contrast imaging.27 Hepatic
lipomas are even rarer than hepatic angiomyolipomas; they consist of
homogeneous macroscopic fat with expected,characteristic imaging
features on both CT and MRI.25,28
Most benign liver tumors, even those of
atypical appearance, may confidently be diagnosed with noninvasive
imaging. Familiarity with the spectrum of imaging appearances of these
exceedingly common tumors is useful in preventing misdiagnoses or
inappropriate invasive interventions. A classification based on the cell
of origin offers an intuitive approach to categorize the myriad benign
- Carrim ZI, Murchison JT. The prevalence of simple renal and hepatic cysts detected by spiral computed tomography. Clin Radiol. 2003;58:626-629.
- Mortelé KJ, Ros PR. Cystic focal liver lesions in the adult: Differential CT and MR imaging features. Radiographics. 2001;21:895-910.
H, Uchida S, Yokokura Y, et al. Nonparasitic solitary huge liver cysts
causing intracystic hemorrhage or obstructive jaundice. J Hepatobiliary Pancreat Surg. 2002;9:764-768.
- Strazzabosco M, Somlo S. Polycystic liver diseases: Congenital disorders of cholangiocyte signaling. Gastroenterology. 2011;140:1855-1859.
- Bockhorn M, Malagó M, Lang H, et al. The role of surgery in Caroli’s disease. J Am Coll Surg. 2006;202:928-932.
- Lev-Toaff AS, Bach AM, Wechsler RJ, et al. The radiologic and pathologic spectrum of biliary hamartomas. AJR Am J Roentgenol. 1995;165: 309-313.
Semelka RC, Hussain SM, Marcos HB, Woosley JT. Biliary hamartomas:
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Lim JH, Jang KT, Rhim H, et al. Biliary cystic intraductal papillary
mucinous tumor and cystadenoma/cystadenocarcinoma: differentiation by
CT. Abdom Imaging. 2007;32:644-651.
- Lim JH, Zen Y, Jang KT, et al. Cyst-forming intraductal papillary
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aspects. AJR Am J Roentgenol. 2011;197:1111-1120.
- Terayama N, Matsui O, Hoshiba K, et al. Peribiliary cysts in liver cirrhosis: US, CT, and MR findings. J Comput Assist Tomogr. 1995;19: 419-423.
- Gupta S, Seith A, Dhiman RK, et al. CT of liver cysts in patients with autosomal dominant polycystic kidney disease. Acta Radiol. 1999;40: 444-448.
Tajima T, Honda H, Kuroiwa T, et al. Radiologic features of
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- Maeda E, Uozumi K, Kato N, et al. Magnetic resonance findings of bile duct adenoma with calcification. Radiat Med. 2006;24:459-462.
IR, Albrecht S, Bilbao J, et al. Multiple focal nodular hyperplasia of
the liver associated with vascular malformation of various organs and
neoplasia of the brain: Anew syndrome. Mod Pathol. 1989;2:456–462.
G, Federle MP, Grazioli L, et al. Focal nodular hyperplasia: CT
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SM, Terkivatan T, Zondervan PE, et al. Focal nodular hyperplasia:
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A, Haraida S, Kraus A, et al. Enhancement of focal liver lesions at
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- Grazioli L, Federle MP, Brancatelli G, et al. Hepatic adenomas: Imaging and pathologic findings. Radiographics. 2001;21:877-892.
- Micchelli ST, Vivekanandan P, Boitnott JK, et al. Malignant transformation of hepatic adenomas. Mod Pathol. 2008;21:491-497.
H, Bioulac-Sage P, Laurent C, et al. Hepatocellular adenomas: Magnetic
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Grazioli L, Bondioni MP, Haradome H, et al. Hepatocellular adenoma and
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- Vilgrain V, Boulos L, Vullierme MP, et al. Imaging of atypical hemangiomas of the liver with pathologic correlation. Radiographics. 2000;20:379-397.
- Brancatelli G, Federle MP, Blachar A, Grazioli L. Hemangioma in the cirrhotic liver: Diagnosis and natural history. Radiology. 2001;219:69-74.
Basaran C, Karcaaltincaba M, Akata D, et al. Fat-containing lesions of
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Hirasaki S, Koide N, Ogawa H, et al. Tuberous sclerosis associated with
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