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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 -

-

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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

8. Welch

dynamic 339-342

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