eMedicine Specialties > Radiology > Gastrointestinal
Focal Nodular Hyperplasia: Imaging
Updated: Feb 3, 2009
Radiography
Findings
Plain radiographs have little to offer in the diagnosis of focal nodular hyperplasia (FNH). Radiographs may demonstrate other causes of abdominal pain in symptomatic patients, including gallstones, nonspecific hepatomegaly, and other soft tissue masses. The presence of calcification in a liver lesion suggests a diagnosis other than FNH because only 1% of patients with FNH have calcification.24
Degree of Confidence
Plain radiography has low specificity and sensitivity in the diagnosis of focal nodular hyperplasia.
Computed Tomography
Enhanced axial CT scan through the liver in the arterial phase in a 38-year-old woman referred for gallbladder scanning (same patient as in Images 2-3). The mass demonstrates intense enhancement.
Delayed portal venous phase enhanced axial CT scan in a 38-year-old woman referred for gallbladder scanning (same patient as in Images 2-4). Image shows stretching of the portal vein and the right hepatic vein around the mass (M).
Findings
On nonenhanced CT scans, focal nodular hyperplasia (FNH) may appear as an isoattenuating or slightly hypoattenuating mass. Nonenhanced images are important because FNH may be missed without a precontrast study (see Images 4-5).
For the optimal evaluation of FNH, a helical CT scan with a 4-phase study should be performed. This evaluation should include nonenhanced and hepatic arterial, portal venous, and delayed–phase examinations.20,25,26
After the administration of contrast material, the lesion becomes hyperattenuating relative to the surrounding liver in the arterial phase; this occurs approximately 20-30 seconds after the bolus of contrast agent is administered. In the portal venous phase, 70-90 seconds after the bolus injection, FNH is less conspicuous and becomes isoattenuating with the rest of the liver. During the delayed phase, approximately 5-10 minutes after the bolus injection, FNH is isoattenuating with normal liver.
In 15-33% of patients, conventional CT scans show the hypoattenuating stellate central scar with a central core and radiating fibrous septa. The central scar may become hyperattenuating on delayed images because of delayed contrast washout from the scar; however, the central scar does not go through a hypoattenuating phase on helical CT scans. The scar is demonstrated as a hyperattenuating region in the portal venous phase. The central artery traversing the central scar may show early enhancement in the arterial phase.
Attal et al described US, CT, and MR features of telangiectatic FNH and correlated their findings with histopathologic findings in 13 cases.27 The study showed that there are a number of differences between telangiectatic FNH lesions and typical FNH lesions: atypical FNH features that are often observed in telangiectatic FNH include the lack of a central scar, lesion heterogeneity, hyperintensity on T1-weighted MRI, strong hyperintensity on T2-weighted MRI, and persistent contrast enhancement on delayed contrast-enhanced CT or T1-weighted MRI.27
Degree of Confidence
When characteristic features are seen in the appropriate clinical setting, one may be fairly confident of the diagnosis. Unfortunately, CT features of other benign and malignant lesions can mimic those of focal nodular hyperplasia (FNH).
Because of the nature and pathogenesis of FNH, it is difficult to obtain an accurate diagnosis of FNH on the basis of the clinical presentation and radiographic studies. Between 1999 and 2006, Shen et al explored the diagnosis and treatment of FNH by studying 86 patients with pathologically confirmed diagnoses of FNH.28 In 80 of the patients, there was a solitary focus; in 6 patients, there were multiple foci. In 69 patients, the diameter of the tumor was less than 5 cm; in 15 patients, the tumor diameter was 5-10 cm; and in 2 patients, the diameter of the tumor was greater than 10 cm.28
Overall, a correct preoperative diagnosis was made in 59.3% of patients (51/86). Doppler color-flow imaging provided a correct preoperative diagnosis in 32.9%; CT provided a correct diagnosis in 60.3%, and MRI, in 77.4%. All of the patients underwent tumor resection, and all displayed good curative results.28
The investigators concluded that CT and MRI are both important methods for diagnosing FNH but that it is difficult to make a definitive preoperative diagnosis in partial classic and in all nonclassic cases of FNH. As a result of their findings, Shen et al suggested that patients undergo tumor resection if they have clinical symptoms or if the diagnosis is indefinite.28
False Positives/Negatives
Although triple-phase CT scanning accurately characterizes most FNH lesions, CT findings are not as definitive in some patients with FNH. Rarely, a false-positive diagnosis of FNH occurs in cases of fibrolamellar hepatocellular carcinoma, as well as in cases involving other well-differentiated variants of hepatocellular carcinoma.
Magnetic Resonance Imaging
Dynamic MRIs in a 36-year-old woman referred for a gallbladder sonography, during which the patient was found to have a vague ill-defined hypoechoic mass in the right lobe of the liver (not shown). (Top left) Gadolinium-enhanced T1-weighted MRI demonstrates an ill-defined low-signal-intensity mass. (Top right) The mass enhances intensely in the arterial phase after the administration of contrast medium. (Bottom left) Minor enhancement persists in the portal venous phase. (Bottom right) The lesion becomes isointense relative to the liver on delayed images.
Findings
Focal nodular hyperplasia (FNH) usually displays a homogeneous signal intensity on MRI (see Image 1).21,29,8,30,31,32
In 94-100% of cases of FNH, the FNH lesion is isointense to hypointense on T1-weighted images; in 6% of cases, the signal intensity on T1-weighted images is hyperintense. On T2-weighted images, the lesion is slightly hyperintense to isointense in 94-100% of cases.
The central scar of FNH is hypointense on T1-weighted images, but on T2-weighted images, the central scar shows a pattern of variable signal intensity. On T2-weighted images, the scar appears hyperintense in 75% of cases; it appears hypointense in 25% of cases.24
After the administration of a gadolinium-based contrast agent, the enhancement pattern parallels that of contrast-enhanced CT. Dense enhancement is seen in the arterial phase; the lesion becomes isointense during the portal venous phase and isointense on delayed images. Late and prolonged enhancement of the central stellate scar occasionally occurs.
MRI findings are not pathognomonic for FNH, but the use of MRI reticuloendothelial agents, such as superparamagnetic iron oxide (SPIO) and ultrasmall superparamagnetic iron oxide (USPIO), increase the specificity. On SPIO-enhanced T2-weighted images, FNH shows decreased signal intensity because of iron uptake by Kupffer cells. This finding is not specific to FNH, because hepatocellular adenoma and hepatocellular carcinoma also may contain Kupffer cells.
Gadolinium-ethoxybenzyl-diethylenetriamine pentaacetic acid (Gd-EOB-DTPA)-enhanced MRI has been shown to be superior to unenhanced MRI alone or spiral CT in the characterization of FNH.33
Attal et al described the features of US, CT, and MRI in cases of telangiectatic FNH; they compared the findings with histopathologic findings in 13 cases of FNH. The results of the study showed that telangiectatic FNH differs from typical FNH on imaging: the atypical features that were often observed with telangiectatic FNH were the lack of a central scar, heterogeneity of lesions, hyperintensity on T1-weighted MRI, strong hyperintensity on T2-weighted MRI, and persistent contrast enhancement on delayed contrast-enhanced CT or T1-weighted MRI.27
Gadolinium-based contrast agents (gadopentetate dimeglumine [Magnevist], gadobenate dimeglumine [MultiHance], gadodiamide [Omniscan], gadoversetamide [OptiMARK], gadoteridol [ProHance]) have been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see the eMedicine topic Nephrogenic Fibrosing Dermopathy. The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MRA scans.
NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble moving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness. For more information, see the FDA Public Health Advisory or Medscape.
Degree of Confidence
For patients with focal nodular hyperplasia (FNH), MRI findings are not pathognomonic for the disease. However, the use of MRI reticuloendothelial agents, such as USPIO and SPIO, can increase the specificity of MRI. In the diagnosis of FNH, MRI has a sensitivity of 70% and a specificity of 98%.24
MRI generally allows differentiation from other hypervascular liver lesions. Moreover, with the development of hepatospecific MRI contrast agents, MRI provides both functional and morphologic information, which is useful in the detection and characterization of FNH lesions.34
False Positives/Negatives
A false-positive diagnosis of FNH may occur with fibrolamellar hepatocellular carcinoma and other well-differentiated forms of hepatocellular carcinoma. On SPIO-enhanced T2-weighted images, hepatocellular adenoma and hepatocellular carcinoma may show decreased signal intensity, because Kupffer cells may be present.
Ultrasonography
Longitudinal sonogram through the liver and gallbladder in a 38-year-old woman referred for gallbladder scanning. Image shows an ill-defined hyperechoic mass in the right lobe of the liver.
Longitudinal sonogram (more medial section than in Image 2) in a 38-year-old woman referred for gallbladder scanning. Sonogram shows mass effect from the tumor, as demonstrated by the arching of the portal vein anteriorly.
Findings
In cases of focal nodular hyperplasia (FNH), US findings are variable. The lesion may appear as a homogeneous mass that is isoechoic, hypoechoic, or hyperechoic. FNH has a mass effect that may displace intrahepatic blood vessels. In only 18% of cases is a central scar present (see Images 2-3).35,36,22
Doppler sonograms demonstrate an enlarged afferent blood vessel with central arterial hypervascularity and centrifugal filling to the periphery in a spokelike manner. Large draining veins may be seen at the periphery of the mass. High-velocity Doppler signals with arterial pulsatility may be recorded from arteriovenous shunts. Echo-enhanced Doppler US has a high sensitivity for detection of the feeding artery and for depiction of the radial vascular architecture in FNH lesions, especially for lesions that are located in the liver's left lobe. Power Doppler US has increased sensitivity for FNH and may help distinguish FNH from hepatocellular carcinoma.
Dynamic contrast-enhanced US is increasingly being used to diagnose FNH. Ungermann et al used dynamic contrast-enhanced US to study the presence of a spoke-wheel pattern and the typical symptoms of FNH, in relation to lesion size, in 28 patients.37 According to the investigators, contrast-enhanced US may be the final diagnostic method for lesions that are larger than 3 cm and have a typical spoke-wheel structure. They concluded, however, that if the spoke-wheel pattern is not present and if there is no central scar, the diagnosis of FNH cannot be made specifically on the basis of contrast-enhanced US alone.37
In a study of 13 cases of FNH, Attal et al described US, CT, and MR features of telangiectatic FNH and correlated their findings with histopathologic findings. They found that telangiectatic FNH differed from typical FNH. The atypical FNH findings that were often observed with telangiectatic FNH were the lack of a central scar, heterogeneous lesion formation, hyperintensity on T1-weighted MRI, strong hyperintensity on T2-weighted MRI, and contrast enhancement on delayed contrast-enhanced CT or T1-weighted MRI.27
Degree of Confidence
The lesion of focal nodular hyperplasia may be difficult to detect, because it is often hypoechoic to normal liver tissue. The specificity of US is low, but the specificity may be increased with Doppler US and echo enhancement. As is the case with other cross-sectional imaging, however, a specific diagnosis is sometimes not possible because the FNH lesion is similar to lesions of other benign and malignant diseases.
False Positives/Negatives
The lesion may be missed entirely if the signal is isoechoic. US findings of FNH overlap those of hepatic adenomas and hepatocellular carcinomas, although the sensitivity and specificity improve with the use of Doppler US, particularly power Doppler and echo-enhanced Doppler US.
Nuclear Imaging
Technetium-99m sulfur colloid scans in a 38-year-old woman referred for gallbladder scanning (same patient as in Images 2-5). Images show complete filling of the mass depicted on sonograms and CT scans.
Findings
The best imaging modalities for characterizing FNH are those modalities that can delineate the lesion's central scar or that can show Kupffer cell activity. The best modalities for identifying the central scar are CT and MRI; Kupffer cell activity is best demonstrated by radionuclide scans. In the future, however, MRI superparamagnetic contrast agents may challenge radionuclide scanning.
Detection of Kupffer cells in FNH has historically been achieved using technetium-99m (99m Tc) sulfur colloid scanning (see Image 6). In 60-70% of FNH patients, these scans show normal or increased uptake of99m Tc sulfur colloid. In 30-40% of patients, Kupffer cells are not sufficiently concentrated in the FNH lesion; the lesion may even be photon deficient.24 The uptake of99m Tc – hepatoiminodiacetic acid (HIDA) is normal or increased in 40-70% of patients, but the lesion may be photon deficient in as many as 60% of patients. With99m Tc-tagged RBCs, uptake is increased during the early phase; subsequently, the uptake is decreased.24
Degree of Confidence
99m Tc sulfur colloid uptake in patients with FNH depends on the concentration of Kupffer cells in the FNH lesion. Unfortunately, other hepatocellular neoplasms, such as a hepatocellular adenoma and hepatocellular carcinoma, may also have Kupffer cells and demonstrate99m Tc sulfur colloid uptake.
False Positives/Negatives
Hepatic adenoma, hemangioma, hepatoblastoma, liver herniation, and hepatocellular carcinoma may be similar in appearance on99m Tc sulfur colloid scans.
Angiography
Findings
Angiographic findings demonstrate a discretely marginated mass. When the mass is small, the arteries supplying the mass break up into small branches, which appear to permeate the FNH and form a reticular pattern. These branches are not dilated, but the overall impression is that of increased vascularity. Vascularity may be decreased within the central stellate scar.
In the parenchymal phase, a fine, homogeneous granularity is demonstrated; occasionally, a lucent ring is seen around the mass.
In large tumors, the dilated main feeding artery perforates the center of the tumor. Peripheral arteries arise from the central artery; these are arranged in a spoke-wheel pattern.
Degree of Confidence
Although the typical angiographic findings are present in only 33% of patients, the diagnosis of FNH may still be suggested.24 FNH may appear similar to an adenoma.
False Positives/Negatives
In only 33% of cases are the characteristic findings of FNH demonstrated; therefore, lesions may be missed, or an incorrect diagnosis, such as a hepatocellular adenoma, may be made in up to 67% of patients.24
More on Focal Nodular Hyperplasia |
| Overview: Focal Nodular Hyperplasia |
 Imaging: Focal Nodular Hyperplasia |
| Follow-up: Focal Nodular Hyperplasia |
| Multimedia: Focal Nodular Hyperplasia |
| References |
| Further Reading |
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Further Reading
Guidelines and clinical studies:
Procedure guideline for hepatic and splenic imaging 3.0. Society of Nuclear Medicine, Inc. 1999 Feb (revised 2003 Jul 20). 5 pages. NGC:003579
ACR Appropriateness Criteria® liver lesion characterization. American College of Radiology. 1998 (revised 2006). 7 pages. NGC:005115
A Comparison of Contrast Enhanced Ultrasound (CEUS) and Contrast Enhanced Computed Tomography (CT) or Magnetic Resonance Imaging (MRI) for Characterization of Focal Liver Masses
Keywords
focal nodular hyperplasia, FNH, liver tumors, hepatic tumors, Kupffer cells, Kupffer's hepatic central stellate scar
