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317
Focal Liver:
Michael J. Le& Sanjay Saini1 Bernd Hamm2 Mathias Taupitz2 Peter F. Hahn1 Eric Seneterre1 Joseph T. Ferrucci1
Nodular
Hyperplasia
MR Findings
of the
in 35 Proved
MR images of 28 patients with 35 lesions of hepatic focal reviewed to determine the frequency of findings considered (isointensity
on Ti-
and
T2-weighted
pulse
sequences,
Cases
nodular hyperplasia were typical of this condition
a central
hyperintense
scar
on
T2-weighted images, and homogeneous signal intensity). Fifteen lesions were imaged at 0.6 T with TI- and T2-weighted spin-echo (SE) pulse sequences; 20 lesions were imaged at 1.5 T with Ti-weighted SE and gradient-echo pulse sequences and T2weighted SE pulse sequences. Diagnosis of focal nodular hyperplasia was made pathologically in 25 patients, with nuclear scintigraphy in four, and with follow-up imaging
in six. Only seven lesions (20%) were isointense relative to normal liver on both Ti- and T2-weighted images. On Ti-weighted SE images, 21 lesions (60%) were isointense relative to normal liver, 12 (34%) were hypointense, and two (6%) were hypenntense. On T2-weighted SE images, 12 lesions (34%) were isointense and 23 (66%) were hyperintense
relative
out the lesion,
except
for the presence
on MR
scar. All three MR imaging
hyperplasia
has
a wide
range
characof signal
imaging.
156:317-320,
AJR
of a central
in three cases (9%). hepatic focal nodular
tenstics were present We conclude that intensity
liver. A central scar was present in 17 lesions (49%) and to the lesion on Ti-weighted images and hyperintense on T2lesions (57%) were of homogeneous signal intensity through-
to normal
was hypointense relative weighted images. Twenty
February
1991
Recently, a number of small series have been published detailing the MR appearances of focal nodular hyperplasia (FNH) [1 -4]. The largest of these [3] concluded that FNH has a fairly consistent MR appearance: (1) isointensity on Ti and T2-weighted sequences; (2) a central scar, which is hyperintense on T2weighted sequences; and (3) homogeneous signal intensity except for the presence of a central scar. However, using improved pulse sequence timing parameters that provide better lesion-liver contrast than those used in previous studies, we noticed more variable signal intensities in our FNH cases. Therefore, we decided to analyze the MR findings in our patients with FNH by performing a retrospective analysis of 35 hepatic FNH lesions, imaged at high and mid field, to determine the prevalence and clinical usefulness of the aforementioned MR characteristics.
-
Received July 27, 1990; accepted August 28, 1990.
after revision
Department of Radiology. Massachusetts General Hospital and Harvard Medical School, 32 Fruit St., Boston, MA 021 14. Address reprint requests to S. Saini. 2 Department of Radiology, Freie Universitat Ber1
in, Universitatsklinikum Steglitz, 30, D 1000 Berlin 45, Germany. 0361-803X/91/1 0 American
562-0317
Roentgen
Ray Society
Hindenburgdamm
Materials
and Methods
patients, six men and 22 women 20-55 years old (mean, 37 years), with 35 liver lesions detected by CT or sonography underwent MR imaging for the purpose of tissue characterization. In i 2 patients with i 5 lesions, MR imaging was performed with a 0.6-T Twenty-eight
imaging system (Teslacon, General Electric Medical Systems, Milwaukee, WI). With the 0.6-T unit, Ti -weighted spin-echo (SE) images, 275/i 4 (TR/TE), and multiecho T2-weighted SE images, 2350/60,i20,i 80, were acquired. Sixteen patients with 20 lesions superconducting
were with
imaged
on a i .5-T superconducting system SE 500/i 5 and gradient-echo
Ti -weighted
(Siemens Magnetom, Erlangen, Germany) (GRE) 1 00/5/80#{176}(TR/TE/flip angle) pulse
318
LEE
sequences
and double-echo
T2-weighted
SE 2500/i
5,90
pulse
with tissue histology
in 25
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sequences.
Pathologic
proof of FNH was obtained
of 35 lesions
needle biopsy core specimens (n = 1 4) or surgical resection (n = i i ). In the remaining i 0 of 35 lesions, diagnosis of FNH was made with mTc sulfur colloid nuclear scintigraphy (n = 4), or typical radiologic features on MR imaging
via percutaneous
(three
unchanged
patients)
with that of adjacent
image,
intensity
formed
of
angiography
central
because
(three
patients),
with
remainder three (9%) previously sity on all the lesion, T2-weighted
AJR:156,
February
1991
had a heterogeneous appearance (Fig. 3). Only of 35 FNH lesions demonstrated all three of the reported [3] typical MR features (Fig. 1) (isointenpulse sequences, signal homogeneity throughout and a central scar of increased signal intensity on images).
an
over
Qualitative analysis by three of the authors weighted
and
6 months. of liver lesions was reaching a consensus
appearance
as compared
i 4- or i 6-gauge
ET AL.
signal scars.
normal liver on each Ti
homogeneity,
and the presence
Quantitative
analysis
of the retrospective
unavailability
of magnetic
large number
of patients.
storage
nature tapes
Discussion
performed in conference on lesion signal intensity
could raw
and
not
of the study
containing
-
T2-
and signal be
per-
and data
the for
a
Results The mean size of all 35 FNH lesions was 5.7 cm (range, 1 .5-1 2.0 cm). On Ti -weighted SE images, 21 (60%) of 35 lesions were isointense relative to normal liver (Fig. 1 A), 12 (34%) were hypointense relative to normal liver (Fig. 2A), and two (6%) were hyperintense relative to normal liver. The hyperintensity in one of these was shown at surgery to represent intralesional hemorrhage (Fig. 3). At 1 .5 T, four of 20 lesions were isointense, whereas the remainder were hypointense relative to normal liver (Figs. 2B and 4) on the more heavily Ti -weighted GRE pulse sequence. On T2weighted SE images 1 2 (34%) of 35 lesions (1 1 were imaged at 0.6 T and one at 1 .5 T) were isointense relative to normal liver (Fig. 1 B); the remaining 23 (66%) of 35 (four were imaged at 0.6 T and 1 9 at 1 .5 T) were hyperintense relative to normal liver (Figs. 2C and 4C). Only seven (20%) of 35 lesions were isointense on all pulse sequences. Further signal intensity classification for each field strength is given in Table 1. In 1 7 (49%) of 35 lesions, a central scar was identified that was hypointense on Ti -weighted and hyperintense on T2weighted images (Figs. 1 and 4). Twenty (57%) of 35 lesions were of homogeneous signal intensity on all imaging sequences, except for the presence of the scar (Fig. 1 ). The
Hepatic FNH is a relatively uncommon benign tumor, occurring in approximately 3% of the adult population [5]. It is typically solitary (80%), occurs primarily in women (85%), and usually is asymptomatic and discovered incidentally. Pathologically, FNH is a nonencapsubated lesion with distorted liver architecture [6]. A central scar is a characteristic gross pathobogic finding. Microscopically, stelbate fibrous bands partially or completely encircle nodules of normal hepatocytes. Recently, several studies [2-4] have proposed that MR imaging may provide a noninvasive tissue-specific diagnosis of FNH, based on the findings of lesion homogeneity, isointensity on Ti - and T2-weighted pulse sequences, and a hyperintense scar on T2-weighted images. Our results, however, suggest that hepatic FNH has a wide range of signal-intensity appearances on MR imaging. Indeed, the isointensity noted in previous studies on Ti - and T2weighted images [2-4] was present in only 20% of our lesions. We believe that this discrepancy from previous reports is due to improvement in pulse sequence timing parameters, which provide increased tissue contrast on Ti - and T2weighted images. For example, Mattison et al. [3] used less heavily Ti -weighted pulse sequences (500/28-60) and vanable T2-weighted pulse sequences (2000/30-i 50) on a lowfield system (0.35 T, Diasonics MT/S). Similarly, Schiebber et ab. [4] used less heavily weighted Ti pulse sequences (600/ 25) on a high-field system (1 .5 T, General Electric Signa). The usefulness of increased Ti weighting, as found by Edelman et al. [7], was evident in our patients when SE and GRE images were compared (i .5 T). In 1 3 of 20 lesions that were isointense relative to liver on Ti -weighted SE images, nine became hypointense relative to liven on Ti -weighted GRE
Fig. 1.-Typical MR findings of focal nodular hyperplasia (0.6 T). A, Ti-weighted MR image (275/14) shows a large, lobulated mass surrounding left portal vein (small arrows). Mass is isointense relative to normal liver, is of homogeneous signal intensity, and contains a central scar (large arrow). B, T2-weighted MR image (2350/180) shows lesion has homogeneous signal intensity and is isointense relative to normal liver. This was true on all T2-weighted images (2350/60,120,180). Central scar (arrow) appears hyperintense on this image.
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AJR:156,
February
1991
MR
OF
HEPATIC
FOCAL
NODULAR
HYPERPLASIA
Fig. 2.-Atypical, nonisointense focal nodular hyperplasia (1.5 T). A and B, Periportal mass (arrows) is hypointense relative to normal liver on Ti-weighted SE 500/15 80#{176} pulse sequence (B). C, Lesion (arrows) is hyperintense relative to normal liver on T2-weighted SE images (2500/15,90). Note absence of a central scar and lesion heterogeneity on both TI- and T2-weighted MR images.
319
pulse
sequence
(A) and TI-weighted
GRE
100/5/
[8]. The MR findings indicate that these scars have a longer Ti and T2 than the body of the lesions, suggesting a higher fractional water content, which is compatible with pathologic observations. The signal intensity of the FNH scar is important, as it may prove to be a valuable differential diagnostic clue. Scars in liver hemangiomas also are watery [9], but on MR images, differences between hemangiomas and FNH are readily appreciated. Central scars in other tumors such as fibnolamellar hepatomas are generally hypointense on Ti - and T2-weighted sequences, as might be expected from a true fibrous scar with poor vascubanity [9]. A single report in the literature describes a central scarlike area in hepatocellular carcinoma, with increased signal intensity on T2-weighted images, mimicking FNH [10]. However, Tiweighted sequences were not performed and no pathologic proof was available, indicating that this scarlike area may have been due to central necrosis. In this series, 20 of 35 lesions were of homogeneous signal intensity on all pulse sequences except for the presence of a
(14%)
Fig. 3.-Atypical focal nodular hyperplasia (0.6 T) on Ti-weighted MR image (275/14). There is no central scar. Large mass in right lobe (arrows) was hyperintense relative to normal liver on both Ti- and T2-weighted pulse sequences, caused by intralesional hemorrhage.
images, because of increased lesion-liven contrast (Fig. 4; Table 1). When results were compared at different field strengths, a discrepancy was noted only on T2-weighted images. The majority of FNH lesions (1 9/20) imaged at 1 .5 T were hypenintense relative to normal liver, whereas at 0.6 T most FNH lesions (1 1/i 5) were isointense relative to normal liver (Table 1). The reason for this discrepancy is not clear, but it may be due to population sampling errors or other unrecognized factors. Central stellate scars were present in 49% of lesions in this series and were hypointense on Ti -weighted images and hypenintense on T2-weighted images. Histopathobogicalby, FNH scars contain bile ducts, blood vessels, and a few or many chronic inflammatory cells. These scars are not commonly detected on other imaging techniques, including CT
scan.
Homogeneity
from
tumors,
alone
which
tend
is unhelpful
in distinguishing
to be heterogeneous
and
FNH hypenin-
tense on T2-weighted sequences, but may be useful when associated with other findings such as a central scar and isointensity on all sequences. In conclusion,
of hepatic of
this
series
illustrates
FNH on MR imaging
appropriate
differential
the
and stresses
diagnostic
varied
appearance
the development
considerations.
When
the characteristic triad of isointensity on Ti - and T2-weighted sequences, lesion homogeneity, and a central hypenintense
scan on T2-weighted
sequences
is present,
the
diagnosis
of
FNH is almost certain. This triad was present in only 9% of patients in this series. However, because on MR images liver metastases are rarely isointense relative to liver, isointensity on either Ti on T2-weighted pulse sequences may be sufficient to discriminate FNH from liven metastases. By using this less rigid criterion of isointensity on either Ti on T2-weighted -
-
LEE
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320
ET AL.
AJR:156,
February
1991
Fig. 4.-Effect of increasing TI weighting (1.5 T) on MR imaging. Two lesions are present. A, On Ti-weighted SE image (500/15), lesions are isointense relative to normal liver and are invisible, except for hypointense central scar (large arrow) and displacement of hepatic vessels (small arrows) in peripherally located lesion. B, On more heavily Ti-weighted GRE image (100/5/80#{176}), lesions become hypointense relative to normal liver (arrows). C, On T2-weighted SE images (2500/15,90), lesions appear hyperintense relative to normal liver (small arrows). Central scar (large arrow) in peripheral area of hyperplasia is hyperintense compared with remainder of lesion.
TABLE
1: MR Signal Intensities
i .5 T
Sequence/Signal Intensity Ti -Weighted
Iso Hypo/hyper Ti -Weighted
(n
Ti
20)
(n
0.6 T = 1 5)
(n
8 (53) 7 (47)
21 (60) 1 4 (40)
13 (65) 7 (35)
REFERENCES
Total = 35)
4(20)
-
-
i 6 (80)
-
-
3.
4. i (5)
1 i (73)
1 2 (34)
Hypo/hyper - and T2-Weighted
1 9 (95)
4 (27)
23 (66)
Iso
0 20 (1 00)
7 (47) 8 (53)
7 (20) 28 (80)
Iso
5.
i3(65)
Hypo/hyper Note-Numbers in parentheses hypo = hyper- or hypointense; SE
12(80)
3 (20)
7 (35) are percentages. =
spin echo;
GRE
Iso =
6.
25(7i)
7.
1 0 (29)
= isointense; gradient echo.
et al. Advances
RJ, Stark DD, Malt RA. MR imaging
in hepatobiliary
of hepatic
focal nodular
hyperplasia.
SE
Hypo/hyper - or T2-Weighted
1 . Ferrucci JT, Freeney PC, Stark DD, radiology. Radiology 1988;1 68:319-338
2. Butch
GRE
Iso
Ti
=
Hyperplasia
SE
Iso
Hypo/hyper T2-Weighted
in Focal Nodular
hyper/
pulse sequences, we can increase diagnostic specificity to 7i % (25/35) (Table i). However, because of fatty change, tumors such as hepatomas also may appear isointense on Ti -weighted images. In this situation, the presence of a typical central scar would increase diagnostic confidence. Further diagnostic specificity may require enhanced dynamic MR imaging [7, ii].
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i989;153:1213-1219 TJ, Sheedy PF, Johnson CM, et al. Focal nodular hyperplasia and hepatic adenoma: comparison of angiography, CT, US, and scintigraphy. Radiology i985;1 56:593-595 9. Aummeny E, Weissleder A, Sironi 5, et al. Central scars in primary liver tumors: MA features, specificity, and pathologic correlation. Radiology i989;171 :323-326 1 0. Wilbur WC, Gyi B. Hepatocellular carcinoma: MA appearance mimicking focal nodular hyperplasia. AJR i987;149:721-722 1 1 . Yoshida H, Itai Y, Ohtomo K, Kokubo T, Minami M, Yashiro N. Small hepatocellular carcinoma and cavernous hemangioma: differentiation with
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