Magnetic resonance (MR) imaging has become a mainstay for the detection and characterization of hepatic lesions, since it can detect and characterize the majority of benign focal liver lesions. This article will review the MR technique and the imaging findings for a variety of benign hepatic lesions.
Dr. Fisher is an instructor in Radiology and a Fellow in
Magnetic Resonance Imaging, and Dr. Siegelman is an Associate
Professor of Radiology and the Chief of the Magnetic Resonance
Imaging Section at the Hospital of the University of
Pennsylvania, Philadelphia, PA.
Magnetic resonance imaging (MRI) has become a mainstay for the
detection and characterization of hepatic lesions. A common
indication is for further evaluation of a mass detected at computed
tomography or ultrasound, particularly discrimination of benign
masses from metastases in a patient with a known extrahepatic
malignancy. This article will review the MR imaging features of
benign hepatic lesions.
At the Hospital of the University of Pennsylvania in
Philadelphia, abdominal MRI is performed on 1.5 Tesla systems with
high-performance gradients. Use of a phased-array multicoil
provides improved image quality and lesion detection in comparison
with the conventional body coil.
T1-weighted images are obtained with breath-hold fast gradient echo
pulse sequences with the echo time (TE) varied to provide both
in-phase and opposed-phase images. These gradient echo sequences
provide the equivalent information of a T1-weighted spin-echo
sequence and also allow for the detection and characterization of
hepatic steatosis and the presence of lipid within hepatocellular
T2-weighted images are acquired using a respiratory-triggered,
fat-saturated, fast-spin echo pulse sequence, which has been shown
to be the optimal technique for obtaining breathing-averaged
T2-weighted abdominal images.
A heavily T2-weighted pulse sequence is acquired using a
breath-hold, single-shot, fast spin-echo pulse sequence with an
effective TE of at least 160 milliseconds. Supplementing moderately
T2-weighted pulse sequences with a heavily T2-weighed pulse
sequence allows improved discrimination of benign cysts and
hemangiomas from hepatic metastases.
A fat-saturated, two-dimensional or three-dimensional
gradient echo T1-weighted sequence allows breath-hold imaging of
the entire liver for precontrast and gadolinium-enhanced images in
the arterial, portal venous, and equilibrium phases.
Simple hepatic cysts are congenital lesions seen in 2.5% of the
population, increasing in prevalence with age and in females.
On MR imaging, hepatic cysts are well-demarcated, round or oval
lesions of very low signal intensity on T1-weighted images and of
very high signal intensity on T2-weighted images with no internal
structures or gadolinium enhancement.
Patients with autosomal-dominant polycystic kidney disease
(ADPCKD) may develop multiple intrahepatic cysts with potential
complications of hemorrhage, infection, biliary obstruction, and,
Patients with ADPCKD may also have peribiliary cysts, which
represent cystic dilation of the peribilary glands that surround
the central bile ducts and are thought to be congenital in
Peribiliary cysts may also be present with extrahepatic portal vein
obstruction, idiopathic portal hypertension, cirrhosis, cirrhosis
with hepatocellular carcinoma, and septicemia.
With severe liver disease, development of peribilary cysts is
probably related to an impaired intrahepatic hemodynamic state,
whereas in septicemia, inflammatory obstruction of glandular
conduits is thought to be causal.
On cross-sectional imaging studies, peribiliary cysts parallel the
portal tracts and may appear as either a string of beads (figure 1)
or as a tubular structure if the individual cyst walls cannot be
The presence of peribiliary cysts on both sides of the larger
portal tracts allows differentiation from dilated bile ducts, which
appear only on one side.
Hemangiomas, the most common benign hepatic neoplasm, are
composed of endothelial-celllined vascular channels with a
supporting fibrous stroma. Hemangiomas demonstrate smooth, round,
or lobular margins.
On T2-weighted images, hemangiomas are hyperintense, approaching
the signal intensity of cerebrospinal fluid (figures 2A and B).
Three patterns of gadolinium enhancement have been described:
immediate homogenous enhancement; peripheral, nodular, centripetal
enhancement progressing to homogeneity; and peripheral nodular
enhancement with a persistent hypointense central region.
Centripetal enhancement is the most common enhancement pattern
(figures 2C through E).
Immediate homogenous enhancement is seen in some hemangiomas
smaller than 1.5 cm.
Rapid filling-in of these smaller hemangiomas is thought to be
related to the smaller vascular spaces and larger interstitium
present in these lesions.
On delayed gadolinium-enhanced images, regions of persistent
central hypointensity in comparison with liver may be present in
hemangiomas larger than 5.0 cm.
Heterogeneity of large or giant hemangiomas is related to the
presence of hemorrhage, thrombosis, extensive hyalinization,
liquefaction, and fibrosis.
On T2-weighted images, the central cleft-like portion (figures 3A
and B) of large hemangiomas is hyperintense in comparison with the
remainder of the mass and corresponds to the region of
hypointensity on the gadolinium-enhanced images (figures 3C and D);
these findings reflect cystic degeneration or liquefaction.
Metastases from neuroendocrine tumors, mucinous adenocarcinomas,
and leiomyosarcomas may mimic hemangiomas or cysts on T2-weighted
Dynamic gadolinium-enhanced images usually allow distinction of
hypervascular or cystic metastases from hemangiomas and benign
Hypervascular hepatic metastases usually demonstrate intact ring
enhancement on images obtained during the arterial phase of
Peripheral enhancement of metastases may be thin-rim, thick-rind,
but not peripheral nodular, like hemangiomas. The peripheral
washout sign, defined as a lesion with a peripheral rim of
hypointensity relative to its center on delayed gadolinium-enhanced
images, has a low sensitivity (24.5%) but 100% specificity for
malignant liver lesions and would therefore exclude a diagnosis of
Outwater et al
found that the subset of rapidly and uniformly enhancing
hemangiomas showed significantly increased signal intensity and
contrast-to-noise ratios on a heavily T2-weighted pulse sequence
allowing discrimination from hypervascular malignant liver lesions,
which may appear identical to hemangiomas on dynamic
Benign hepatocellular neoplasms
Cysts, hemangiomas, and metastases appear hypointense to liver
on T1-weighted images due to increased free water protons. Hepatic
masses isointense or hyperintense to liver on T1-weighted images
obtained with high-field magnets are usually of hepatocellular
This specificity for hepatocellular masses does not necessarily
apply for T1-weighted images obtained with low-field magnets or
magnets with nonenhanced gradients that preclude use of a TE short
enough to avoid T2-weighted contamination.
Focal nodular hyperplasia
Focal nodular hyperplasia (FNH) is considered to be a
hyperplastic response of hepatic parenchyma to a preexisiting
This benign tumor-like lesion contains disorganized nodules of
hepatocytes and Kupffer cells without central veins or portal
tracts. The nodules are separated by fibrous septa, which contain
small bile ducts that lack communication with the normal biliary
FNH is usually solitary (70% to 80% of cases) and is usually <5
cm in diameter.
FNH is most often found in women (80% to 95% of cases) in their
third or fourth decades of life, but can occur at all ages and in
Oral contraceptive medications do not cause, but may promote, the
growth of FNH.
Typical MR imaging features of FNH include isointensity or
slight hypointensity compared with liver on T1-weighted images and
slight hyperintensity or isointensity compared with liver on
T2-weighted images (figures 4A through C).
FNH is usually homogenous in signal intensity except for a central
scar, which is hypointense to the lesion and surrounding liver on
T1-weighted images and hyperintense on T2-weighted images.
After administration of gadolinium-chelates, FNH shows marked
hyperintensity in the arterial phase and isointensity in the portal
venous phase (figures 4D and E).
The central scar demonstrates late enhancement.
This characteristic pattern of MR imaging findings is seen in
approximately 50% to 70% of these lesions.
Atypical imaging features of FNH include nonvisualization or
nonenhancement of the central scar.
Hepatocellular adenoma is a benign neoplasm of hepatocytes with
an absence of normal portal structures.
Hepatocellular adenomas are seen in association with use of oral
and glycogen storage disease types I and III.
Complications include acute hemorrhage (seen in 50% of patients in
) and rare malignant transformation.
On MR imaging, hepatic adenomas have a variable appearance with
heterogeneity often seen on either the T1-weighted or T2-weighted
On T1-weighted images, the majority of hepatic adenomas have
portions that are hyperintense or isointense to the liver (figure
Hyperintensity on T1-weighted images can be due to the presence of
intratumoral lipid, hemorrhage, or concentrated hepatocytes.
Chemical shift imaging can confirm the presence of lipid.
Most commonly, hepatic adenomas have components that are
hyperintense to surrounding liver on T2-weighted images, although
they can be isointense or hypointense (figure 5F).
Heterogeneity on T2-weighted images is related to hemorrhage or
In the report by Chung et al,
13 of 15 adenomas showed early enhancement on dynamic breath-hold
gradient echo imaging (figure 5B). Arterial enhancement of hepatic
adenoma is not as great as that of FNH, and a central scar is not
Arrive et al
identified a peritumoral rim in 31% of hepatic adenomas. Pathologic
correlation in all cases revealed a pseudocapsule composed of
compressed adjacent hepatic parenchyma and mild fibrosis. The
peripheral rim was usually hypointense to liver on T1-weighted
images. On T2-weighted images, the rim had variable signal
intensity and was hypointense, isointense, or hyperintense to
adjacent liver. In the 11 cases in which gadolinium was
administered, only 2 showed enhancement of the rim.
At least one of the following three imaging features was found
by Arrive et al
in 88% of hepatic adenomas: tumor heterogeneity, peripheral
pseudocapsule, or hyperintensity on T1-weighted spin-echo images.
These features may allow differentiation from FNH, but not from
hepatocellular carcinoma, and pathologic evaluation is recommended.
The probability of a lesion representing either a hepatic adenoma
or hepatocellular carcinoma can often be predicted based on the
clinical setting, as hepatic adenomas usually occur in young women
on oral contraceptive medications and hepatocellular carcinoma
usually occurs in older men with chronic hepatitis cirrhosis.
Liver adenomatosis is a distinct clinical entity defined by the
presence of multiple (arbitrarily >10) hepatic adenomas in an
otherwise normal liver.
In contrast to liver adenoma, liver adenomatosis affects both men
and women, is unrelated to use of oral contraceptive medications,
and is commonly associated with increases in serum alkaline
phosphatase and g-glutamyl transpeptidase.
The MR imaging characteristics of individual lesions in liver
adenomatosis are similar to those occurring in women using oral
Hepatic abscesses may be pyogenic, fungal, or amebic in
etiology. In the United States, most hepatic abscesses are
pyogenic, but worldwide, amebic abscesses are the most common.
Pyogenic abscesses originate from biliary or hematogenous sources.
Biliary sources include cholecystitis or ascending cholangitis, as
well as complications from biliary surgery or interventional
Hematogenous spread may occur through the portal vein from enteric
sources or the hepatic artery in septicemia.
The MR imaging appearance of hepatic abscesses is nonspecific.
The clinical history is often contributory. The presence of
multiple lesions demonstrating high T2-weighted signal,
perilesional edema, and rim enhancement is suggestive of abscesses.
Mendez et al
reported a cluster of small abscesses found in 5 of 8 patients with
pyogenic abscesses of biliary origin. This "cluster sign" is an
insensitive but specific finding of pyogenic abscess (figure 6B),
and is rarely present with metastatic disease.
Rim enhancement of abscesses assists in the discrimination from
other lesions with high T2-weighted signal such as cysts and
Hepatosplenic fungal disease is usually caused by Candida and
occurs in the setting of profound neutropenia. MR imaging has
proven superior to CT in detecting hepatosplenic fungal disease.
In the acute presentation (¾ 2 weeks of possible infection), fungal
microabscesses are seen as foci of high signal intensity on
fat-suppressed T2-weighted images.
The lesions are minimally hypointense to liver on both unenhanced
and enhanced T1-weighted images, and perilesional enhancement is
not observed in most patients.
Focal hepatic steatosis and focal fatty sparing
Focal hepatic steatosis and focal fatty sparing can result in
hepatic "pseudolesions" that may be mistaken for malignancy.
Chemical shift imaging can confirm the presence of microscopic
lipid with loss of signal intensity demonstrated on opposed-phase
images in comparison with in-phase images (figures 7A through C).
Imaging features suggestive of focal hepatic steatosis or sparing
include periligamentous and periportal locations, geographic
margins with lack of mass effect, and lack of distortion of
traversing blood vessels.
Decreased portal venous blood supply to the medial segment of the
left hepatic lobe from aberrant gastric venous drainage is thought
to result in the fatty sparing in this location (figures 8A and B).
Focal fatty sparing or pseudolesions around the falciform ligament
may be due to aberrant blood supply from the internal thoracic
Why focal hepatic steatosis can occur in the same locations as
focal fatty sparing is uncertain, but it may be due to decreased
delivery of unknown substances from the portal vein or relative
ischemia secondary to diminished portal venous supply.
Magnetic resonance can detect and characterize the majority of
benign focal liver lesions. The ability to detect intratumoral
lipid, characterize hepatocellular neoplasms, and distinguish
between solid and nonsolid liver lesions makes MR an ideal imaging
modality for hepatic lesion evaluation.