DOI:10.2214/AJR.05.1368
AJR 2007; 188:154-159
© American Roentgen Ray Society
Transient Hepatic Intensity Differences: Part 1, Those Associated with Focal Lesions
Stefano Colagrande1,
Nicoletta Centi1,
Roberta Galdiero2 and
Alfonso Ragozzino2
1 Department of Clinical Physiopathology, Section of Radiodiagnostics,
University of Florence, Viale Morgagni 85, Florence 50134, Italy.
2 Section of Radiodiagnostics, Ospedale SM Grazie Pozzuoli, Naples, Italy.
Received August 8, 2005;
accepted after revision October 21, 2005.
Address correspondence to S. Colagrande
(stefano.colagrande{at}unifi.it)
Abstract
OBJECTIVE. The purpose of our study was to evaluate, on MRI,
transient hepatic signal intensity differences (THID) that have already been
seen on CT as transient hepatic attenuation differences (THAD) and to show the
range of appearance of such arterial phenomena, when associated with focal
lesions, in an effort to correlate morphology, cause, and pathogenesis.
CONCLUSION. Hepatic arterial phenomena visualized on MRI should be
known and recognized to avoid incorrect diagnoses and to improve the
characterization of focal liver lesions because their shape can lead to an
understanding of pathogenetic mechanisms.
Keywords: arterial phenomena • dynamic MRI • hemodynamics • liver • liver disease • liver perfusion abnormalities • MRI • THID • transient hepatic intensity differences
Introduction
Transient hepatic attenuation differences (THAD) are areas of parenchymal
enhancement visible during the hepatic artery phase on helical CT that are
caused by the dual hepatic blood supply. In fact, there are compensatory
relationships between two liver sources of blood supply so that arterial flow
increases when portal flow decreases as a result of communication among the
main vessels, sinusoids, and peribiliary venules that open in response to
autonomic nervous system and humoral factors activated by liver demand for
oxygen and metabolites.
Today hepatic arterial phase evaluation may also be easily performed on
MRI, on which perfusion alterations can also be observed; we call these
"transient hepatic signal intensity differences" (THID). Perfusion
phenomena have been associated with many liver disorders
[1-3].
This article intends to show the range of appearance on MRI of such arterial
phenomena as has already been shown for helical CT
[2], using the same
comprehensive diagnostic organization that attempts to correlate morphology,
cause, and pathogenesis.
The first ascertainable feature of transient hepatic intensity differences
is an association with a focal liver lesion. Therefore, we have organized our
article into two parts, the first regarding transient hepatic intensity
differences associated with a focal lesion, and the second
[4] concerning transient
hepatic intensity differences without a focal lesion.
Focal lesions can determine two morphologic types of transient hepatic
intensity differences through four pathogenetic mechanisms: directly by a
siphoning effect (lobar multisegmental shape) or indirectly by means of portal
hypoperfusion (sectorial shape) due to portal branch compression or
infiltration, by thrombosis resulting in a portal branch blockade, or by flow
diversion caused by an arterioportal shunt.
Lobar Multisegmental Shape
Lobar multisegmental transient hepatic intensity differences occur when a
hypervascular focal lesion, usually large and benign, or an abscess induces an
increase in the primary arterial inflow, which leads to surrounding parenchyma
hyperperfusion (the "siphoning effect"), in the absence of any
demonstrable portal hypoperfusion. These signal intensity differences do not
assume a triangular shape; nevertheless, a straight border (a clear line that
separates arterial phenomena from adjacent parenchyma) may be present. A
hypervascular tumor likely acts on the right or left hepatic artery, producing
enhancement of the hepatic lobe containing the lesion
[2,
5,
6] (Figs.
1A,
1B,
1C, and
1D).
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Fig. 1A —34-year-old woman with fibronodular hyperplasia in left
hepatic lobe determining homolateral lobar transient hepatic intensity
difference (lobar siphoning effect). Axial T2-weighted MR image (TR/TE,
830/80) shows slightly hyperintense nodule (arrow) in left hepatic
lobe.
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Fig. 1B —34-year-old woman with fibronodular hyperplasia in left
hepatic lobe determining homolateral lobar transient hepatic intensity
difference (lobar siphoning effect). Axial gradient-echo T1-weighted
gadolinium-enhanced arterial phase MR images (216/1.5) show rapid enhancement
of lesion (arrow, B) and arterial phenomenon
(arrowheads) of parenchyma in segments II-IV.
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Fig. 1C —34-year-old woman with fibronodular hyperplasia in left
hepatic lobe determining homolateral lobar transient hepatic intensity
difference (lobar siphoning effect). Axial gradient-echo T1-weighted
gadolinium-enhanced arterial phase MR images (216/1.5) show rapid enhancement
of lesion (arrow, B) and arterial phenomenon
(arrowheads) of parenchyma in segments II-IV.
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Fig. 1D —34-year-old woman with fibronodular hyperplasia in left
hepatic lobe determining homolateral lobar transient hepatic intensity
difference (lobar siphoning effect). Axial gradient-echo T1-weighted
gadolinium-enhanced portal phase MR image (216/1.5) shows no parenchymal
enhancement in segments II-IV.
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Sometimes smaller tumors are active on the primary branch of the right or
left hepatic artery, with segmental siphoning and signal hyperintensity only
of the segment containing the tumor (Figs.
2A,
2B, and
2C); on the contrary, rarely,
the contralateral segment in the hepatic lobe containing the tumor may show
lower signal intensity than the opposite lobe (the tumor "steals"
blood flow from the ipsilobar contralateral segment)
[6]. Biochemical mediators, if
any, are unknown; increased arterial inflow and consequential hyperenhancement
may simply be caused by arterial vascular bed enlargement due to tumor
("sump effect"). In that way, the remainder of the healthy
parenchyma surrounding the tumor can also receive a greater blood supply than
usual [5,
6].
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Fig. 2A —58-year-old woman with hemangioma in left hepatic lobe
inducing homolateral transient hepatic intensity difference in liver segment
II (segmental siphoning effect). Axial T2-weighted MR image (TR/TE, 862/320)
shows highly hyperintense nodule (arrow) in left hepatic lobe,
segment II.
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Fig. 2B —58-year-old woman with hemangioma in left hepatic lobe
inducing homolateral transient hepatic intensity difference in liver segment
II (segmental siphoning effect). Axial gradient-echo T1-weighted
gadolinium-enhanced arterial phase MR images (216/1.5) show enhanced lesion
(arrow, B) and arterial phenomenon (arrowheads)
involving only parenchyma of segment II.
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Fig. 2C —58-year-old woman with hemangioma in left hepatic lobe
inducing homolateral transient hepatic intensity difference in liver segment
II (segmental siphoning effect). Axial gradient-echo T1-weighted
gadolinium-enhanced arterial phase MR images (216/1.5) show enhanced lesion
(arrow, B) and arterial phenomenon (arrowheads)
involving only parenchyma of segment II.
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Fig. 3A —58-year-old woman with inflammatory pseudotumor in right
hepatic lobe causing homolateral lobar transient hepatic intensity difference
(lobar siphoning effect). Axial T2-weighted MR image (TR/TE, 12,000/84) shows
large hyperintense mass (arrow).
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Fig. 3B —58-year-old woman with inflammatory pseudotumor in right
hepatic lobe causing homolateral lobar transient hepatic intensity difference
(lobar siphoning effect). Axial gradient-echo T1-weighted gadolinium-enhanced
arterial phase MR images (146/2) show hypointense pseudotumor (arrow,
B) and arterialization (arrowheads) surrounding lesion.
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Fig. 3D —58-year-old woman with inflammatory pseudotumor in right
hepatic lobe causing homolateral lobar transient hepatic intensity difference
(lobar siphoning effect). Axial T2-weighted (12,000/82) (D) and axial
gradient-echo T1-weighted (E) gadolinium-enhanced arterial phase
(146/2) MR images obtained 3 months after A and B show
pseudotumor size reduction (D) and consequent disappearance of arterial
phenomenon (E). Note right pleural effusion.
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Fig. 3E —58-year-old woman with inflammatory pseudotumor in right
hepatic lobe causing homolateral lobar transient hepatic intensity difference
(lobar siphoning effect). Axial T2-weighted (12,000/82) (D) and axial
gradient-echo T1-weighted (E) gadolinium-enhanced arterial phase
(146/2) MR images obtained 3 months after A and B show
pseudotumor size reduction (D) and consequent disappearance of arterial
phenomenon (E). Note right pleural effusion.
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Fig. 4A —43-year-old man with large subcapsular liver abscess in right
lobe producing homolateral lobar transient hepatic intensity difference (lobar
siphoning effect). Axial T2-weighted MR image (TR/TE, 12,000/84) shows large
hyperintense lesion (arrow).
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Fig. 4B —43-year-old man with large subcapsular liver abscess in right
lobe producing homolateral lobar transient hepatic intensity difference (lobar
siphoning effect). Axial gradient-echo T1-weighted gadolinium-enhanced
arterial phase MR image (146/2) shows hypointense mass and lobar
arterialization (arrowheads) in surrounding parenchyma.
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In cases of phlogistic lesions (Figs.
3A,
3B,
3C,
3D,
3E,
4A, and
4B), inflammatory mediators
spread in the parenchyma around the lesion and induce hyperemia and then the
sump effect. In addition, the same generic benign histologic type can be
associated with lobar transient hepatic intensity differences if the nodule is
large so that the sump effect occurs, or associated with sectorial
arterialization, if the lesion is small and induces portal hypoperfusion (by
means of compression, an arterioportal shunt, or portal thrombosis). This
phenomenon may occur not only in abscesses (Figs.
4A,
4B,
5A, and
5B) but also in association
with angiomas or other focal benign lesions. Finally, when the causal focal
lesion becomes smaller, vanishing of the siphoning effect can be observed as
well (Figs. 3A,
3B,
3C,
3D, and
3E).
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Fig. 5A —32-year-old man with liver abscess in right lobe that is
inducing sectorial wedge-shaped transient hepatic intensity difference. Axial
T2-weighted MR image (TR/TE, 12,000/84) shows hyperintense lesion
(arrow) in segment V.
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Fig. 5B —32-year-old man with liver abscess in right lobe that is
inducing sectorial wedge-shaped transient hepatic intensity difference. Axial
gradient-echo T1-weighted gadolinium-enhanced arterial phase MR image (146/2)
shows sectorial arterial phenomenon (arrowhead) in right hepatic lobe
due to portal hypoperfusion secondary to portal branch thrombosis
(arrow) induced by abscess.
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Sectorial Shape
Sectorial transient hepatic intensity differences follow portal vessel
dichotomy and appear as triangular areas, with at least a straight border that
is a result of the strict relationship between the portal hypoperfused area
and the arterial reaction.
Sectorial transient hepatic intensity differences are associated not only
with benign or malignant (
70%) tumors
[7] but also with liver
abscesses, probably due to portal hypoperfusion as well as to the spread of
inflammatory mediators [8]
(Figs. 5A and
5B). They can be either wedge-
or fan-shaped [2], depending on
where the associated focal lesion is situated.
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Fig. 6A —50-year-old man with small round hemangioma beneath Glisson's
capsule in right hepatic lobe and intralesional arterioportal shunt producing
sectorial wedge-shaped arterial phenomenon. Axial T2-weighted (TR/TE, 830/80)
(A) and axial gradient-echo unenhanced T1-weighted (216/1.5) (B)
MR images show right hepatic lobe nodule (arrow) that is strongly
hyperintense in A and hypointense in B.
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Fig. 6B —50-year-old man with small round hemangioma beneath Glisson's
capsule in right hepatic lobe and intralesional arterioportal shunt producing
sectorial wedge-shaped arterial phenomenon. Axial T2-weighted (TR/TE, 830/80)
(A) and axial gradient-echo unenhanced T1-weighted (216/1.5) (B)
MR images show right hepatic lobe nodule (arrow) that is strongly
hyperintense in A and hypointense in B.
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Fig. 6C —50-year-old man with small round hemangioma beneath Glisson's
capsule in right hepatic lobe and intralesional arterioportal shunt producing
sectorial wedge-shaped arterial phenomenon. Axial gradient-echo T1-weighted
iron-oxide-enhanced arterial phase (C) and 10-minute delayed phase
(D) MR images (216/1.5) show wedge-shaped arterial phenomenon
(arrowhead, C) of parenchyma and late enhancement of
hemangioma (arrow, D).
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Fig. 6D —50-year-old man with small round hemangioma beneath Glisson's
capsule in right hepatic lobe and intralesional arterioportal shunt producing
sectorial wedge-shaped arterial phenomenon. Axial gradient-echo T1-weighted
iron-oxide-enhanced arterial phase (C) and 10-minute delayed phase
(D) MR images (216/1.5) show wedge-shaped arterial phenomenon
(arrowhead, C) of parenchyma and late enhancement of
hemangioma (arrow, D).
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Fig. 6E —50-year-old man with small round hemangioma beneath Glisson's
capsule in right hepatic lobe and intralesional arterioportal shunt producing
sectorial wedge-shaped arterial phenomenon. Axial sonogram (E),
pulsed-wave Doppler sonogram (F), and color Doppler sonogram (G)
(all obtained with convex, 3.5-MHz probe) show sectorial hypoechoic area
(spare in fatty liver) that has same location and shape as sectorial arterial
phenomenon (E), arteriovenous pulsed waves (F), and color
pattern flow (G) inside hemangioma, indicating an intralesional
shunt.
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Fig. 6F —50-year-old man with small round hemangioma beneath Glisson's
capsule in right hepatic lobe and intralesional arterioportal shunt producing
sectorial wedge-shaped arterial phenomenon. Axial sonogram (E),
pulsed-wave Doppler sonogram (F), and color Doppler sonogram (G)
(all obtained with convex, 3.5-MHz probe) show sectorial hypoechoic area
(spare in fatty liver) that has same location and shape as sectorial arterial
phenomenon (E), arteriovenous pulsed waves (F), and color
pattern flow (G) inside hemangioma, indicating an intralesional
shunt.
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Fig. 6G —50-year-old man with small round hemangioma beneath Glisson's
capsule in right hepatic lobe and intralesional arterioportal shunt producing
sectorial wedge-shaped arterial phenomenon. Axial sonogram (E),
pulsed-wave Doppler sonogram (F), and color Doppler sonogram (G)
(all obtained with convex, 3.5-MHz probe) show sectorial hypoechoic area
(spare in fatty liver) that has same location and shape as sectorial arterial
phenomenon (E), arteriovenous pulsed waves (F), and color
pattern flow (G) inside hemangioma, indicating an intralesional
shunt.
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When an associated focal lesion is inside the arterial phenomenon,
centrally or laterally positioned, and induces an arterioportal shunt (Figs.
6A,
6B,
6C,
6D,
6E,
6F, and
6G) or portal thrombosis
(Figs. 7A,
7B, and
7C), the sectorial transient
hepatic intensity difference is wedge-shaped. Because arterioportal shunts
occur frequently in hepatocellular carcinoma, arterial phenomena associated
with this malignancy are common; nevertheless, they are more frequently caused
by large tumors inducing portal vein invasion or thrombosis.
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Fig. 7A —65-year-old man with liver cirrhosis and hepatocellular
carcinoma causing sectorial wedge-shaped transient hepatic intensity
difference induced by portal thrombosis secondary to tumor. Axial
gradient-echo T1-weighted gadolinium-enhanced arterial phase MR image (TR/TE,
146/2) shows strongly enhancing nodule (white arrow) and related
satellite (black arrow).
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Fig. 7B —65-year-old man with liver cirrhosis and hepatocellular
carcinoma causing sectorial wedge-shaped transient hepatic intensity
difference induced by portal thrombosis secondary to tumor. Axial
gradient-echo T1-weighted gadolinium-enhanced arterial phase MR image (146/2)
shows arterialization (black arrowhead) and portal thrombosis
(white arrowhead).
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Fig. 7C —65-year-old man with liver cirrhosis and hepatocellular
carcinoma causing sectorial wedge-shaped transient hepatic intensity
difference induced by portal thrombosis secondary to tumor. Axial T2-weighted
MR image (12,000/82) confirms portal thrombosis (arrowhead) and shows
slight signal intensity changes in triangular area of arterial phenomenon due
to small increase in amount of free water.
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In nodular lesions smaller than 3 cm, the incidence of arterioportal shunts
is higher in angiomas (21%) than in hepatocellular carcinomas (4%)
[1,
9]. In these cases, shunts lead
to a mixing of venous low-pressure and arterial high-pressure blood and then
to portal flow diversion, with relative portal hypoperfusion of contiguous
parenchyma and an arterial reaction. If persistent, these changes can
determine focal metabolic alterations, resulting in a triangular area, fatty
in normal liver or spare in fatty liver (Figs.
6A,
6B,
6C,
6D,
6E,
6F, and
6G).
When an associated focal lesion is situated at the apex of the arterial
phenomenon and causes portal compression (Figs.
8A,
8B, and
8C) or portal branch
infiltration (Figs. 9A and
9B), the sectorial transient
hepatic intensity difference is fan-shaped; this shape is the type most
frequently linked to malignancies (Figs.
10A,
10B, and
10C).
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Fig. 8A —27-year-old woman with echinococcus cyst and sectorial
fan-shaped transient hepatic intensity difference. Axial T2-weighted MR image
(TR/TE, 12,000/84) shows hyperintense round cyst (arrow) and slight
hyperintensity of liver parenchyma at site of arterial phenomenon
(arrowheads), probably due to increase in amount of free water.
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Fig. 8B —27-year-old woman with echinococcus cyst and sectorial
fan-shaped transient hepatic intensity difference. Axial gradient-echo
T1-weighted gadolinium-enhanced arterial phase MR images (TR/TE, 146/2) show
lesion (arrows) positioned at apex of fan-shaped arterial phenomenon
(arrowheads) caused by portal compression.
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Fig. 8C —27-year-old woman with echinococcus cyst and sectorial
fan-shaped transient hepatic intensity difference. Axial gradient-echo
T1-weighted gadolinium-enhanced arterial phase MR images (TR/TE, 146/2) show
lesion (arrows) positioned at apex of fan-shaped arterial phenomenon
(arrowheads) caused by portal compression.
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Fig. 9A —56-year-old man with sectorial fan-shaped transient hepatic
intensity difference associated with cholangiocellular carcinoma. Axial
iodinated contrast-enhanced arterial phase helical CT image shows sectorial
arterial phenomenon (arrowheads) apparently not associated with focal
lesion.
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Fig. 9B —56-year-old man with sectorial fan-shaped transient hepatic
intensity difference associated with cholangiocellular carcinoma. Axial
gradient-echo T1-weighted gadolinium-enhanced arterial phase MR image (TR/TE,
216/1.5) obtained 3 months after A shows small hypointense focal lesion
(arrow) at apex of fan-shaped arterial phenomenon, causing portal
branch infiltration and subsequent portal hypoperfusion.
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Fig. 10A —59-year-old man with large hepatic intraparenchymal
metastasis from colon carcinoma and correlated sectorial fan-shaped transient
hepatic intensity difference. Axial T2-weighted MR image (TR/TE, 12,000/84)
shows hyperintense parahilar nodule (arrow) with associated slight
signal intensity change (arrowhead) due to small increase in amount
of free water. Note small fluid collection near Glisson's capsule.
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Fig. 10B —59-year-old man with large hepatic intraparenchymal
metastasis from colon carcinoma and correlated sectorial fan-shaped transient
hepatic intensity difference. Axial gradient-echo fat-suppressed T1-weighted
unenhanced (146/2) (B) and axial gradient-echo fat-suppressed
T1-weighted gadolinium-enhanced arterial phase (146/2) (C) MR images
show wide fan-shaped arterial phenomenon with straight border
(arrowhead, C) due to hypointense neoplastic lesion at its
apex (arrow), causing portal compression. Note how segment III is
also slightly enhanced. Although this transient hepatic intensity difference
could look like lobar type because of distribution, this arterial phenomenon
is undoubtedly sectorial because lesion, being hypodense and hypoenhancing,
causes portal compression and not a primary increase in arterial flow.
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Fig. 10C —59-year-old man with large hepatic intraparenchymal
metastasis from colon carcinoma and correlated sectorial fan-shaped transient
hepatic intensity difference. Axial gradient-echo fat-suppressed T1-weighted
unenhanced (146/2) (B) and axial gradient-echo fat-suppressed
T1-weighted gadolinium-enhanced arterial phase (146/2) (C) MR images
show wide fan-shaped arterial phenomenon with straight border
(arrowhead, C) due to hypointense neoplastic lesion at its
apex (arrow), causing portal compression. Note how segment III is
also slightly enhanced. Although this transient hepatic intensity difference
could look like lobar type because of distribution, this arterial phenomenon
is undoubtedly sectorial because lesion, being hypodense and hypoenhancing,
causes portal compression and not a primary increase in arterial flow.
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Transient hepatic intensity differences are not usually seen on T2-weighted
images, probably because no changes occur in the amount of free water in the
area of the differences [7];
however, when arterial reaction is intense, a slight T2 hyperintensity can be
observed (Figs. 7A,
7B,
7C,
8A,
8B,
8C,
10A,
10B, and
10C).
Sometimes arterial phenomena have no clear explanation. When the arterial
phenomenon is due to portal hypoperfusion caused by a focal lesion, the
diameter of the causal lesion is not related to the area (size) of the
arterial phenomenon; then a small lesion can cause a wide area of
arterialization. As a consequence, a sectorial arterial phenomenon may
sometimes be the only warning sign of a hidden nodular lesion that is not
detectable for size or contrast reasons and yet causes portal compression. In
these cases, arterialization may herald an underlying abnormality and precedes
the MRI or CT detection of the nodular lesion (Figs.
9A and
9B). The latter possibility
must be considered whenever a sectorial arterialization has no other
explanation [10].
Finally, arterial phenomena not connected to a focal liver lesion, due to
cirrhosis, to an arterioportal shunt, or to a small portal branch thrombosis,
may have a round appearance and might mimic a hypervascular nodule, making
diagnosis difficult [1] (see
part 2 of this article
[4]).
Conclusion
As happens at CT, arterial phenomena are visualized more and more often on
MRI because of the shorter acquisition time. These phenomena should be known
and recognized to avoid an incorrect diagnosis and to improve the
characterization of focal liver lesions because their shape can lead to
understanding of the pathogenic mechanisms.
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M. Torabi, K. Hosseinzadeh, and M. P. Federle
CT of Nonneoplastic Hepatic Vascular and Perfusion Disorders1
RadioGraphics,
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1967 - 1982.
[Abstract]
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F. Hughes-Cassidy, J. Wong, D. Aguirre, A. D. Chavez, T. Wolfson, A. Gamst, and C. Sirlin
Transient Homogeneously Enhancing Hepatic Masses: Can Size Predict Benignity?
Am. J. Roentgenol.,
February 1, 2008;
190(2):
300 - 307.
[Abstract]
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[PDF]
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S. Colagrande, N. Centi, R. Galdiero, and A. Ragozzino
Transient Hepatic Intensity Differences: Part 2, Those Not Associated with Focal Lesions
Am. J. Roentgenol.,
January 1, 2007;
188(1):
160 - 166.
[Abstract]
[Full Text]
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Abstract
Introduction
