Hyperintense benign liver lesions on spin-echo T1-weighted MR images: pathologic correlations

How to Differentiate Borderline Hepatic Nodules in Hepatocarcinogenesis: Emphasis on Imaging Diagnosis

BACKGROUND

Rapid advances in liver imaging have improved the evaluation of hepatocarcinogenesis and early diagnosis and treatment of hepatocellular carcinoma (HCC). In this situation, detection of early-stage HCC in its development is important for the improvement of patient survival and optimal treatment strategies. Because early HCCs are considered precursors of progressed HCC, precise differentiation between a dysplastic nodule (DN), especially a high-grade DN, and early HCC is important. In clinical practice, these nodules are frequently called "borderline hepatic nodules."

SUMMARY

This article discusses radiological and pathological characteristics of these borderline hepatic nodules and offers an understanding of multistep hepatocarcinogenesis by focusing on the descriptions of the imaging changes in the progression of DN and early HCC. Detection and accurate diagnosis of borderline hepatic nodules are still a challenge with contrast enhanced ultrasonography, CT, and MRI with extracellular contrast agents. However, gadoxetic acid-enhanced MRI may be useful for improving the diagnosis of these borderline nodules.

KEY MESSAGES

Since there is a net effect of incomplete neoangiogenesis and decreased portal venous flow in the early stage of hepatocarcinogenesis, borderline hepatic nodules commonly show iso- or hypovascularity. Therefore, precise differentiation of these nodules remains a challenging issue. In MRI using hepatobiliary contrast agents, signal intensity of HCCs on hepatobiliary phase (HBP) is regarded as a potential imaging biomarker. Borderline hepatic nodules are seen as nonhypervascular and hypointense nodules on the HBP, which is important for predicting tumor behavior and determining appropriate therapeutic strategies.

MR characterization of focal liver lesions: pearls and pitfalls

Magnetic resonance (MR) can characterize specific tissue subtypes, thus facilitating focal liver lesion diagnosis. Focal liver lesions that are isointense to hyperintense to liver on T1-weighted images are usually hepatocellular in origin. Chemical shift imaging can narrow the differential diagnosis by detecting the presence of lipid or iron. T2 and heavily T2-weigthed fast spin echo imaging can differentiate solid from nonsolid focal liver lesions. The authors illustrate these MR imaging pearls and the uncommon exceptions (pitfalls). The authors hope that you will find this less traditional contribution to the Magnetic Resonance Clinics of North America helpful in clinical practice.

Magnetic resonance imaging in cirrhosis: what's new?

Cirrhosis is the main risk factor for the development of hepatocellular carcinoma (HCC). The major causative factors of cirrhosis in the United States and Europe are chronic hepatitis C infection and excessive alcohol consumption with nonalcoholic steatohepatitis emerging as another important risk factor. Magnetic resonance imaging is the most sensitive imaging technique for the diagnosis of HCC, and the sensitivity can be further improved with the use of diffusion-weighted imaging and hepatocyte-specific contrast agents. The combination of arterial phase hyperenhancement, venous or delayed phase hypointensity "washout feature," and capsular enhancement are features highly specific for HCC with reported specificities of 96% and higher. When these features are present in a mass in the cirrhotic liver, confirmatory biopsy to establish the diagnosis of HCC is not necessary. Other tumors, such as cholangiocarcinoma, sometimes occur in the cirrhotic at a much lower rate than HCC and can mimic HCC, as do other benign lesions such as perfusion abnormalities. In this article, we discuss the imaging features of cirrhosis and HCC, the role of magnetic resonance imaging in the diagnosis of HCC and other benign and malignant lesions that occur in the cirrhotic liver, and the issue of nonspecific arterially hyperenhancing nodules often seen in cirrhosis.

MR findings of steatotic focal nodular hyperplasia and comparison with other fatty tumours

OBJECTIVES

To correlate MR findings with pathology in steatotic FNHs and to compare the MR findings with those of other fatty tumours developed on noncirrhotic liver in a consecutive series of resected lesions.

METHODS

Our population included resected FNH with intralesional steatosis (n = 25) and other resected fatty tumours selected as controls (hepatocellular adenomas and angiomyolipomas, n = 34). Lesions were classified into three groups: those with typical FNH without (group 1) or with (group 2) fat on MR and those with atypical lesions (group 3). In group 3, diagnostic criteria for other fatty tumours were applied.

RESULTS

There were 9 lesions in group 1 (15.3 %), 4 in group 2 (16.8 %) and 46 in group 3 (77.9 %). Group 3 contained 12 FNHs (26 %) and all the other fatty tumours. In group 3, the association of lesion homogeneity, signal intensity similar to or slightly different from adjacent liver on in-phase T1- and T2-weighted sequences, and strong arterial enhancement was observed in 7/12 (58 %) of steatotic FNHs and 3/34 (9 %) of other tumours.

CONCLUSION

On MR, fat within a typical FNH should not reduce the diagnostic confidence. We recommend further investigations including liver biopsy if necessary when fatty tumours exhibit atypical MR findings.

Imaging of multifocal hepatic lesions in pediatric patients

Imaging plays a vital role in detection and characterization of multifocal liver lesions in children. Numerous causes for these lesions exist, including benign and malignant neoplasms, infectious lesions, and congenital and inflammatory conditions. The imaging spectrum of multifocal liver lesions in children is presented with emphasis on key imaging features, differential diagnoses and helpful relevant clinical features.

Systematic review of haemorrhage and rupture of hepatocellular adenomas

BACKGROUND

Although benign in itself, hepatocellular adenoma (HCA) can be complicated by hormone-induced growth, and subsequent haemorrhage and rupture. The exact risk of haemorrhage and rupture is not known. This systematic review of the literature was carried out with the aim of estimating the risk of haemorrhage and rupture in HCA.

METHODS

A systematic literature search of the PubMed and Embase databases was performed for all articles relevant to haemorrhage and/or rupture of HCA, published between 1969 and March 2011.

RESULTS

Twenty-eight articles met the selection criteria, containing a total of 1176 patients. Haemorrhage was reported with an overall frequency of 27·2 per cent among patients, and in 15·8 per cent of all HCA lesions. Rupture and intraperitoneal bleeding were reported in 17·5 per cent of patients. Bleeding was the first symptom in 68·5 per cent of patients with a bleeding HCA. Six of 13 articles reporting the size of HCA lesions in which bleeding occurred mentioned haemorrhage in HCAs smaller than 5 cm.

CONCLUSION

Haemorrhage and rupture are common in patients with HCA.

Gamut of focal fatty lesions in the liver: imaging manifestations with emphasis on magnetic resonance imaging

A wide variety of hepatic lesions contain fat within them in a proportion good enough to be demonstrable on imaging. With the biological behaviors quite different from each other, they form a clinico-radio-pathologic spectrum worth remembering. We present a review of common and uncommon focal hepatic lesions containing fat (micro- and macroscopic) within them and emphasize the role of imaging in their diagnosis.

Magnetic resonance imaging of the liver: New imaging strategies for evaluating focal liver lesions

The early detection of focal liver lesions, particularly those which are malignant, is of utmost importance. The resection of liver metastases of some malignancies (including colorectal cancer) has been shown to improve the survival of patients. Exact knowledge of the number, size, and regional distribution of liver metastases is essential to determine their resectability. Almost all focal liver lesions larger than 10 mm are demonstrated with current imaging techniques but the detection of smaller focal liver lesions is still relatively poor. One of the advantages of magnetic resonance imaging (MRI) of the liver is better soft tissue contrast (compared to other radiologic modalities), which allows better detection and characterization of the focal liver lesions in question. Developments in MRI hardware and software and the availability of novel MRI contrast agents have further improved the diagnostic yield of MRI in lesion detection and characterization. Although the primary modalities for liver imaging are ultrasound and computed tomography, recent studies have suggested that MRI is the most sensitive method for detecting small liver metastatic lesions, and MRI is now considered the pre-operative standard method for diagnosis. Two recent developments in MRI sequences for the upper abdomen comprise unenhanced diffusion-weighted imaging (DWI), and keyhole-based dynamic contrast-enhanced (DCE) MRI (4D THRIVE). DWI allows improved detection (b = 10 s/mm²) of small (< 10 mm) focal liver lesions in particular, and is useful as a road map sequence. Also, using higher b-values, the calculation of the apparent diffusion coefficient value, true diffusion coefficient, D, and the perfusion fraction, f, has been used for the characterization of focal liver lesions. DCE 4D THRIVE enables MRI of the liver with high temporal and spatial resolution and full liver coverage. 4D THRIVE improves evaluation of focal liver lesions, providing multiple arterial and venous phases, and allows the calculation of perfusion parameters using pharmacokinetic models. 4D THRIVE has potential benefits in terms of detection, characterization and staging of focal liver lesions and in monitoring therapy.

Focal liver lesions hyperintense on T1-weighted magnetic resonance images

This article reviews focal liver lesions hyperintense on T1-weighted magnetic resonance (MR) images and describes the underlying etiologies associated with their T1 signal intensity. Although focal liver lesions are commonly detected because of their iso- or hypointensity on T1-weighted images, lesions (benign or malignant) may present with T1 hyperintensity when they contain T1 shortening elements--such as fat, hemorrhage, copper, melanin, and highly concentrated proteins. Our discussion includes the description of state-of-the-art T1-weighted MR sequences and the imaging features of lesions on pre- and postcontrast MR images that are characteristic for lesion composition and useful for making accurate diagnosis.

MR Imaging of hepatocellular carcinoma in the cirrhotic liver: challenges and controversies

The incidence of hepatocellular carcinoma (HCC) is expected to increase in the next 2 decades, largely due to hepatitis C infection and secondary cirrhosis. HCC is being detected at an earlier stage owing to the implementation of screening programs. Biopsy is no longer required prior to treatment, and diagnosis of HCC is heavily dependent on imaging characteristics. The most recent recommendations by the American Association for the Study of Liver Diseases (AASLD) state that a diagnosis of HCC can be made if a mass larger than 2 cm shows typical features of HCC (hypervascularity in the arterial phase and washout in the venous phase) at contrast material-enhanced computed tomography or magnetic resonance (MR) imaging or if a mass measuring 1-2 cm shows these features at both modalities. There is an ever-increasing demand on radiologists to detect smaller tumors, when curative therapies are most effective. However, the major difficulty in imaging cirrhosis is the characterization of hypervascular nodules smaller than 2 cm, which often have nonspecific imaging characteristics. The authors present a review of the MR imaging and pathologic features of regenerative nodules and dysplastic nodules and focus on HCC in the cirrhotic liver, with particular reference to small tumors and lesions that may mimic HCC. The authors also review the sensitivity of MR imaging for the detection of these tumors and discuss the staging of HCC and the treatment options in the context of the guidelines of the AASLD and the imaging criteria required by the United Network for Organ Sharing for transplantation. MR findings following ablation and chemoembolization are also reviewed.

Small hyperintense hepatic lesions on T1-weighted images in patients with cirrhosis: evaluation with serial MRI and imaging features for clinical benignity

PURPOSE

The aim of this study was to evaluate the frequency and magnetic resonance imaging (MRI) features of clinically benign, small (<2 cm) hyperintense hepatic lesions in the cirrhotic liver on T1-weighted MR images seen at serial MRI.

MATERIALS AND METHODS

This study included 189 patients with cirrhosis, who underwent hepatic MRI more than twice with an interval of at least 12 months. The initial MR images were reviewed for the presence of small hyperintense lesions on T1-weighted images. The size, location and signal intensity on T2-weighted images as well as enhancement patterns of the corresponding lesions were recorded.

RESULTS

On the initial T1-weighted MR images, 43 small hyperintense hepatic lesions were detected in 23 (12%) of 189 patients. Twelve (28%) of 43 lesions showed early enhancement and were pathologically diagnosed as hepatocellular carcinoma (HCC) during the follow-up period. Thirty-one (72%) of 43 lesions showed no early enhancement with various signal intensity on T2-weighted images (hyperintensity=4, isointensity=20, hypointensity=7). Among these 31 lesions, 12 showed no interval change, while 11 disappeared (n=10) or decreased in size (n=1). In the remaining eight lesions, seven were diagnosed as HCC on the basis of pathologic confirmation or the interval growth.

CONCLUSION

Small hyperintense hepatic lesions on T1-weighted magnetic resonance (MR) images without early enhancement on the arterial-phase contrast-enhanced dynamic studies in patients with cirrhosis usually showed no interval growth or disappeared during the serial MRI. These lesions with additional findings of iso- or hypointensity on the T2-weighted MR images without "washout effect" on the contrast-enhanced equilibrium-phase images may more frequently be clinically benign or hyperplastic nodules than HCCs.

Fat-containing nodules in the cirrhotic liver: chemical shift MRI features and clinical implications

OBJECTIVE

The purpose of this study was to determine the ability of MRI to predict malignancy in fat-containing nodules in the cirrhotic liver.

MATERIALS AND METHODS

In 38 patients with cirrhotic livers, focal lesions > or = 5 mm containing fatty components were identified on chemical shift gradient-echo MRI. Positive predictive values (PPVs) for benignity and malignancy were calculated on the basis of lesion size, T1-weighted hypointensity, T2-weighted hyperintensity, and arterial hypervascularity on the initial MR images. The number of the fatty nodules (group A, up to 4; group B, numerous) in individual patients was also correlated with the malignant potential of the lesions that were verified pathologically or by follow-up imaging studies.

RESULTS

In 31 group A patients, 21 (47%) of the 45 lesions showed a malignant course, and their mean diameter (18.8 mm) was larger (p = 0.007) than that (10.5 mm) of benign lesions. In seven group B patients, all 35 lesions (the five largest lesions in each patient; mean diameter, 7.8 mm) proved to be benign. The PPV of larger (> or = 15 mm) fat-containing nodules for malignancy was 85% (11/13 lesions). Six (55%) of 11 immediately diagnosed hepatocellular carcinomas were entirely hypointense on unenhanced in-phase T1-weighted images. The PPV of T2-weighted hyperintensity and arterial hypervascularity for the diagnosis of malignancy was 100% in group A patients.

CONCLUSION

In the cirrhotic liver, large size (> or = 15 mm) and T1-weighted hypointensity on in-phase images strongly suggest malignancy of the fat-containing nodules. The presence of numerous nodules < 1 cm suggests that the lesions are benign.

Use of accumulation images obtained by arterial-phase contrast-enhanced harmonic grayscale ultrasonography to evaluate tumor vessels in focal nodular hyperplasia and other hepatic tumors

PURPOSE

To evaluate the usefulness of accumulation images obtained by arterial-phase contrast-enhanced harmonic grayscale ultrasonography for examining tumor vessels in focal nodular hyperplasia and other hepatic lesions.

METHODS

After injecting a galactose-palmitic acid contrast agent, we used conventional contrast-enhanced harmonic grayscale ultrasonography to scan 8 focal nodular hyperplasia lesions, 21 hepatocellular carcinomas, 2 cholangiocellular carcinomas, 12 hepatic metastases, 17 hemangiomas, and 2 angiomyolipomas. We then accumulated and superimposed consecutive conventional images (accumulation images) and compared them with corresponding conventional images to evaluate serial images of hepatic tumor vessels.

RESULTS

Serial tumor vessel findings obtained from accumulation images were superior to those obtained from conventional images in 51 (77%) of the 66 various hepatic lesions examined. Evidence of the spoke-wheel artery pattern in 2 of the 8 focal nodular hyperplasia lesions was equivocal in the conventional images, but accumulation images clearly depicted serial images of spoke-wheel arteries, clearly indicating a diagnosis of focal nodular hyperplasia. Accumulation images allowed the diagnosis of two additional focal nodular hyperplasia lesions that had not been correctly diagnosed as focal nodular hyperplasia from conventional images.

CONCLUSION

Accumulation images obtained by arterial-phase contrast-enhanced harmonic grayscale ultrasonography are useful in evaluating hepatic tumor vessels, especially spoke-wheel arteries, which specifically indicate focal nodular hyperplasia.

Fat-containing lesions of the liver: radiologic-pathologic correlation

Fat-containing tumors of the liver are a heterogeneous group of tumors with characteristic histologic features, variable biologic profiles, and variable imaging findings. Benign liver lesions that contain fat include focal or geographic fatty change (steatosis), pseudolesions due to postoperative packing material (omentum), adenoma, focal nodular hyperplasia, lipoma, angiomyolipoma, cystic teratoma, hepatic adrenal rest tumor, pseudolipoma of the Glisson capsule, and xanthomatous lesions in Langerhans cell histiocytosis. Malignant liver lesions that can contain fat include hepatocellular carcinoma, primary and metastatic liposarcoma, and hepatic metastases. Identification of fat within a liver lesion can be critical in characterization of the lesion. The imaging characteristics of a lesion coupled with the pattern of intratumoral fatty change are helpful in narrowing the differential diagnosis. Although the presence of fat can be demonstrated with computed tomography or ultrasound, magnetic resonance imaging is the most specific imaging technique for demonstration of both microscopic and macroscopic fat.

Diagnosis of focal nodular hyperplasia of the liver by needle biopsy

Focal nodular hyperplasia (FNH) of the liver can be a difficult diagnosis to establish in limited diagnostic samples such as a needle-core tissue biopsy, especially for pathologists with limited experience with the lesion. To characterize the features that can be used to make the diagnosis, we reviewed and analyzed the clinicopathologic features of 100 consecutive cases submitted for consultation in which we were confident of the diagnosis of FNH in needle biopsy material. A diagnosis of FNH was correctly made by the contributing pathologist in 24 of the 100 referred cases. Most of the patients (81%) were women of childbearing age with a mean age of 36.75 +/- 9.82 years. Most of the patients (70%) were asymptomatic at diagnosis. The most consistent diagnostic histological feature of FNH in needle biopsy was the presence of ductular reaction with varied intensity at the junction of the fibrous septa with the hepatocellular component, which was present in all 100 cases. Thick abnormal arteries were seen in all but 2 cases (n = 98). Features of chronic cholestasis with cholate stasis and accumulation of copper (demonstrable by the rhodanine stain) and copper-binding protein (demonstrable with the Victoria blue stain) were nearly as common (n = 94). A confident diagnosis of FNH can be made with a needle biopsy, especially if the biopsy is known to come from a mass, and the lesion contains characteristic fibrosis with ductules at the interface between hepatocytes and the fibrous region, prominent arteries, and benign hepatocytes with features of chronic cholestasis.

MRI of atypical focal nodular hyperplasia of the liver: radiology-pathology correlation

OBJECTIVE

The purpose of our study was to determine the MRI features of atypical focal nodular hyperplasia of the liver and to compare them to pathology findings.

MATERIALS AND METHODS

We retrospectively reviewed MRI and pathology findings in 27 focal nodular hyperplasia lesions with atypical MRI features. Six criteria for typical focal nodular hyperplasia were required: iso- or hypointensity on T1-weighted sequences and iso- or slight hyperintensity on T2-weighted sequences; homogeneous signal intensity; central hyperintense area on T2-weighted sequences; marked lesion contrast enhancement; accumulation of gadolinium chelates within the central area on delayed contrast-enhanced T1-weighted sequences; and absence of capsule.

RESULTS

The most common atypical radiology features included absence of, or an atypical, stellate area; heterogeneity on both T1- and T2-weighted images; and high-intensity signal on T1-weighted sequences. MRI-pathology correlation showed that T1 hyperintensity with no other atypical MRI feature (n = 3) could be explained by steatosis, sinusoidal dilatation, or hemorrhage. In addition, in two patients with lesions smaller than 3 cm in diameter, the only atypical MRI feature was absence of a stellate area.

CONCLUSION

These findings suggest a lesion that is hyperintense on T1-weighted sequences or that lacks a stellate area but is smaller than 3 cm in diameter can be diagnosed as focal nodular hyperplasia provided all other MRI criteria for this diagnosis are present. In such cases, close monitoring on MRI without invasive diagnostic procedures may be warranted. However, in large lesions (> 3 cm) without a stellate area and in lesions with heterogeneity, histopathology examination is mandatory to rule out other diagnoses.

Evaluation of hepatic focal nodular hyperplasia with contrast-enhanced gray scale harmonic sonography: initial experience

OBJECTIVE

To assess the potential of contrast-enhanced gray scale harmonic sonography in the evaluation of the typical vascular and enhancement patterns of hepatic focal nodular hyperplasia.

METHODS

Thirteen patients with 13 lesions of hepatic focal nodular hyperplasia underwent contrast-enhanced gray scale harmonic sonography. After the injection of a microbubble contrast agent (SH U 508A), gray scale harmonic sonographic studies using a Coded Harmonic Angio technique were performed with a combination of a period of continuous scanning to assess the vascular pattern (vascular imaging) and interval delay scanning to determine the sequential enhancement pattern (acoustic emission imaging). Each imaging pattern was categorized and analyzed by consensus of 2 experienced radiologists.

RESULTS

In 12 (92%) of 13 lesions, vascular imaging during the arterial phase showed central arteries of a spoked wheel pattern, whereas the remaining lesion had stippled vascularity. On acoustic emission imaging, 11 (85%) of 13 lesions were hyperechoic during the early phase, and the remaining 2 (15%) were isoechoic compared with surrounding parenchyma. Ten (77%) of 13 lesions remained either hyperechoic (5 of 13) or isoechoic (5 of 13) during the delay phase, whereas the remaining 3 lesions (23%) were hypoechoic.

CONCLUSIONS

Contrast-enhanced gray scale harmonic sonography showed the typical vascularity of a spoked wheel pattern during the vascular phase and persistent enhancement on serial acoustic emission imaging in most cases of hepatic focal nodular hyperplasia, and thereby it can be a promising technique in noninvasive diagnosis of this entity.

Telangiectatic focal nodular hyperplasia: US, CT, and MR imaging findings with histopathologic correlation in 13 cases

PURPOSE

To review the ultrasonographic (US), computed tomographic (CT), and magnetic resonance (MR) imaging findings in 13 patients with telangiectatic focal nodular hyperplasia (FNH) and to compare imaging features with histopathologic results from resected specimens.

MATERIALS AND METHODS

US, helical multiphasic CT, and MR images in 13 patients with pathologically proven telangiectatic FNH were reviewed retrospectively. Two abdominal radiologists evaluated lesions for number, size, heterogeneity, surface characteristics, presence of a central scar, presence of a pseudocapsule, US appearance, attenuation at CT, signal intensity at MR imaging, and presence of associated lesions. Imaging and pathologic findings were compared.

RESULTS

Sixty-one lesions (5-140 mm in diameter) were seen at imaging. Lesions were multiple in eight of 13 (62%) patients. Imaging characteristics were heterogeneity in 26 of 61 lesions (43%), well-defined margins in 43 of 61 (70%), lack of a central scar in 56 of 61 (92%), presence of a pseudocapsule in three of 61 (5%), hyperintensity on T1-weighted MR images in 17 of 32 (53%), strong hyperintensity on T2-weighted MR images in 24 of 54 (44%), and persistent enhancement on delayed contrast material-enhanced CT or T1-weighted MR images in 23 of 38 (61%). No specific US pattern was noted. Two patients had additional lesions: One had classic FNH, and the other had a cavernous hemangioma. Hyperintensity on T1-weighted MR images was due to sinusoidal dilatation. Hyperintensity on T2-weighted MR images correlated well with the presence of inflammation.

CONCLUSION

Telangiectatic FNH differs from typical FNH at imaging: Atypical FNH features often observed with telangiectatic FNH are lack of a central scar, lesion heterogeneity, hyperintensity on T1-weighted MR images, strong hyperintensity on T2-weighted MR images, and persistent contrast enhancement on delayed contrast-enhanced CT or T1-weighted MR images.

Atypical focal nodular hyperplasia of the liver: imaging features of nonspecific and liver-specific MR contrast agents

OBJECTIVE

The objective of our study was to describe the functional and differential uptake features of atypical focal nodular hyperplasia using different MR contrast agents and to evaluate their potential role in the diagnosis and characterization of focal nodular hyperplasia.

MATERIALS AND METHODS

Contrast-enhanced MR images of 45 patients with 85 focal nodular hyperplasia lesions were retrospectively reviewed. In these patients, sonographic findings were nonspecific (n = 37), or CT features were inconclusive (n = 8). Non-liver specific gadolinium chelates were used in 18 patients (48 lesions) suspected of having either focal nodular hyperplasia or hemangioma. The following liver-specific agents were used in patients with suspected focal nodular hyperplasia or metastases: mangafodipir trisodium, 30 patients (55 lesions); ferumoxides, six patients (16 lesions); and SHU 555 A, six patients (six lesions). Individual lesions were quantified by signal intensity and assessed qualitatively by homogeneity, contrast enhancement, and presence of a central scar.

RESULTS

At unenhanced MR imaging, the triad of homogeneity, isointensity, and central scar was found in 22% of the focal nodular hyperplasia lesions. On mangafodipir trisodium-enhanced T1-weighted images, all focal nodular hyperplasia lesions showed contrast uptake: in 64% of the lesions, uptake was equal to parenchyma; 25%, greater than the parenchyma; and 11%, less than the parenchyma. On iron oxide-enhanced T2-weighted images, all focal nodular hyperplasia lesions showed uptake of the contrast agent, but contrast uptake in the lesions was less than in the surrounding parenchyma. Dynamic gadolinium chelate-enhanced MR imaging showed early and vigorous enhancement of focal nodular hyperplasia lesions with rapid washout in 88%. Atypical imaging features of the lesions included hyperintensity on T1-weighted images, necrosis and hemorrhage, and inhomogeneous or only minimal contrast uptake.

CONCLUSION

For patients in whom the diagnosis of focal nodular hyperplasia cannot be established on unenhanced or gadolinium-enhanced MR imaging, homogeneous uptake of liver-specific contrast agent with better delineation of central scar may help to make a confident diagnosis of focal nodular hyperplasia.

CT findings and mistopathology of intratumoral steatosis in focal nodular hyperplasia: case report and review of the literature

Focal nodular hyperplasia (FNH) is a benign hepatic lesion characterized by homogeneous enhancement following intravenous contrast. The authors report a patient with a markedly heterogeneous FNH due to extensive intratumoral fat.

Histologic scoring of liver biopsy in focal nodular hyperplasia with atypical presentation

The contribution of radio-guided transcutaneous biopsy in the diagnosis of focal nodular hyperplasia (FNH) of the liver was compared with the findings on surgical specimens to assess its contribution in clinical and radiologic atypical cases. This retrospective study involved 30 patients with atypical tumors on imaging who underwent liver biopsy and then surgery. All surgical specimens were diagnosed as FNH, either classical (n = 18) or nonclassical (n = 12). Imaging data were reviewed according to 4 radiologic criteria on magnetic resonance imaging (MRI) and/or computed tomography (CT) scan (hypervascularity, homogeneity, nonencapsulation, and presence of a central scar), and classified depending on the number of criteria found (group I, 4 of 4; group II, 3 of 4; group III, 2 or fewer). Histologic assessment of ultrasound (US)-guided liver biopsy recorded major diagnostic features (fibrous bands, thick-walled vessels, reactive ductules, and nodularity) and minor features (sinusoidal dilatation and perisinusoidal fibrosis). "Definite FNH" (3 or 4 major features) was diagnosed in 14 biopsies, "possible FNH" (2 major and 1 or 2 minor features) in 7 cases, and "negative for FNH" (2 or fewer major features without minor features) in 9 cases. The diagnosis of FNH on biopsy was reached in 14 cases (58.3%) in patients with 2 or fewer imaging criteria (group III; n = 24). Biopsies with a diagnosis of "possible FNH" corresponded to a large proportion of telangiectatic-type FNH on the specimen. In conclusion, liver biopsy does not appear to be necessary in cases in which imaging is typical. However, the absence of radiologic diagnostic criteria in FNH does not preclude a positive diagnosis on liver needle biopsy. Using the proposed histologic scoring system, surgical management may be avoided in these cases.

Benign liver neoplasms

A variety of benign focal liver lesions are easily characterized with currently available imaging techniques and contrast agents. The most common benign liver lesions, such as hemangioma, bile duct cyst, and FNH, reveal characteristic cross-sectional imaging features that allow an accurate diagnosis. For atypical variants and more uncommon lesions, including HCA, angiomyelioma, infantile hemagioendothelioma, and mesenchymal hamartoma, integration of clinical data can often help in the interpretation of imaging studies. Finally, for the remaining lesions, such as hepatic adenomatosis, the imaging findings may not be specific enough to negate the need for a tissue biopsy.

Magnetic resonance imaging techniques

In this article we describe state-of-the art techniques for magnetic resonance imaging of the liver. T1-weighted, T2-weighted, and heavily T2-weighted pulse sequences are discussed. Gadolinium-enhanced hepatic parenchymal imaging and magnetic resonance angiography are also described. A comprehensive MR imaging examination of the liver affords evaluation of focal and diffuse hepatic parenchymal disease, biliary disease, and vascular pathology.

Imaging the fatty liver

Even though various imaging techniques are available to detect fat, chemical-shift imaging is the most accurate for both qualitative and quantitative measurement of fat. It can be very useful in liver studies, not only because it definitively demonstrates fatty liver but also because it improves lesion detection and characterization in some cases.

Nondiffuse fatty change of the liver: discerning pseudotumor on MR images enhanced with ferumoxides-initial observations

PURPOSE

To clarify the findings of nondiffuse fatty change of the liver on ferumoxides-enhanced magnetic resonance (MR) images.

MATERIALS AND METHODS

Of 202 patients who underwent ferumoxides-enhanced MR imaging, eight who had nondiffuse fatty change of the liver at computed tomography (CT) were examined as study subjects. MR imaging findings before and 1 hour after ferumoxides administration were compared with CT findings.

RESULTS

Focal fatty areas of the liver showing low attenuation on CT images were depicted as areas of relatively high intensity on the ferumoxides-enhanced T1-weighted images in all patients. On enhanced T2-weighted images, focal fatty change showed relatively high intensity in three and isointensity in one of the four patients. Focal spared areas appearing as areas of relatively high attenuation on CT images were depicted as areas of relatively low intensity on the ferumoxides-enhanced T1- and T2-weighted images in all patients.

CONCLUSION

Although prior reports of hepatic MR imaging with ferumoxides indicated that there is accumulation of ferumoxides within focal fatty areas that are no longer seen after the administration of contrast medium, this study revealed that focal fatty change and focal spared areas of fatty liver may be pseudotumors because of the relatively high intensity of fatty areas of the liver. Radiologists can distinguish these conditions from hepatic tumors by using the opposed-phase gradient-echo sequence or the fat-saturation technique.

Magnetic resonance imaging (MRI) and diseases of the liver and biliary tract. Part 1. Basic principles, MRI in the assessment of diffuse and focal hepatic disease

Magnetic resonance imaging (MRI) relies on the physical properties of unpaired protons in tissues to generate images. Unpaired protons behave like tiny bar magnets and will align themselves in a magnetic field. Radiofrequency pulses will excite these aligned protons to higher energy states. As they return to their original state, they will release this energy as radio waves. The frequency of the radio waves depends on the local magnetic field and by varying this over a subject, it is possible to build the images we are familiar with. In general, MRI has not been sufficiently sensitive or specific in the assessment of diffuse liver disease for clinical use. However, because of the specific characteristics of fat and iron, it may be useful in the assessment of hepatic steatosis and iron overload. Magnetic resonance imaging is useful in the assessment of focal liver disease, particularly in conjunction with contrast agents. Haemangiomas have a characteristic bright appearance on T2 weighted images because of the slow flowing blood in dilated sinusoids. Focal nodular hyperplasia (FNH) has a homogenous appearance, and enhances early in the arterial phase after gadolinium injection, while the central scar typically enhances late. Hepatic adenomas have a more heterogenous appearance and also enhance in the arterial phase, but less briskly than FNH. Hepatocellular carcinoma is similar to an adenoma, but typically occurs in a cirrhotic liver and has earlier washout of contrast. The appearance of metastases depends on the underlying primary malignancy. Overall, MRI appears more sensitive and specific than computed tomography with contrast for the detection and evaluation of malignant lesions.

Fibrolamellar carcinoma of the liver: radiologic-pathologic correlation

Fibrolamellar carcinoma is a malignant hepatocellular tumor with distinct clinical and pathologic differences from hepatocellular carcinoma. It differs from hepatocellular carcinoma in demographics, condition of the affected liver, tumor markers, and prognosis. Fibrolamellar carcinoma characteristically manifests as a large hepatic mass in adolescents or young adults (without gender predominance). Cirrhosis; elevated alpha-fetoprotein levels; and typical risk factors for hepatocellular carcinoma such as viral hepatitis, alcohol abuse, and metabolic disease are typically absent. Fibrolamellar carcinoma is characterized pathologically by cords of tumor cells surrounded by abundant collagenous fibrous tissue arranged in a parallel or lamellar distribution. Fibrotic lamellae often coalesce to form a central scar. Fibrolamellar carcinoma characteristically appears on radiologic images as a lobulated heterogeneous mass with a central scar in an otherwise normal liver. Radiologic evidence of cirrhosis, vascular invasion, or multifocal disease--findings typical of hepatocellular carcinoma--is uncommon in fibrolamellar carcinoma. Imaging features of fibrolamellar carcinoma overlap with those of other scar-producing lesions including focal nodular hyperplasia (FNH), hepatocellular adenoma and carcinoma, hemangioma, metastases, and cholangiocarcinoma. FNH, in particular, may simulate fibrolamellar carcinoma, since both have similar demographic and clinical characteristics. Because some believe that radiologic diagnosis of FNH is possible, it is important to understand the imaging appearance of fibrolamellar carcinoma to avoid misdiagnosing this malignant tumor as a FNH.

Magnetic resonance imaging of focal and diffuse hepatic disease

MRI is a powerful tool in the detection and characterization of both focal and diffuse liver pathology. Because of superior soft tissue characterization, direct multi-planar capabilities and lack of ionizing radiation, current state of the art MRI is useful when contrast CT is relatively contraindicated or not definitive. This article reviews the MRI findings of the most common focal and diffuse liver diseases encountered in clinical practice. Reviews of current MR techniques and MR contrast agents used in liver imaging have been recently published. For this article, discussion of specific techniques and use of contrast is addressed for each pathological entity discussed.