(Radiographics. 1999;19:431-451.)
© RSNA, 1999
CT and MR Imaging of Benign Hepatic and Biliary Tumors
Karen M. Horton, MD1,
David A. Bluemke, MD1,
Ralph H. Hruban, MD2,
Philippe Soyer, MD, PhD3 and
Elliot K. Fishman, MD1
1 Departments of Radiology (K.M.H., D.A.B., E.K.F.)
2 Pathology (R.H.H.), Johns Hopkins Hospital, Baltimore, Md
3 Department of Body and Vascular Imaging, Hospital Lariboisiere, Paris, France (P.S.)
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Abstract
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Benign hepatic and biliary tumors can present a difficult diagnostic challenge. Spiral computed tomography (CT) and magnetic resonance (MR) imaging are useful in the detection and characterization of these tumors. Imaging characteristics of lesions such as hepatic cyst, hemangioma, focal nodular hyperplasia (FNH), and hepatic adenoma are well known. Hepatic cysts demonstrate water attenuation at CT, are isointense relative to water at MR imaging, and do not enhance after intravenous administration of contrast material. Hemangiomas demonstrate characteristic nodular peripheral enhancement on early-phase images with subsequent fill-in centrally at both modalities. FNH classically demonstrates intense early enhancement with washout on delayed images. Although hepatic adenoma can also demonstrate intense early enhancement, it has a tendency to bleed and thus often appears more heterogeneous than FNH due to hemorrhage. Benign hepatic tumors that are less well described in the imaging literature include hepatic lipoma or angiomyolipoma, infantile hemangioendothelioma, and mesenchymal hamartoma. Hepatic lipoma has fat attenuation at CT, is isointense relative to fat at MR imaging, and does not enhance after intravenous administration of contrast material. Hepatic angiomyolipomas contain a variable amount of soft tissue in addition to fat and may therefore demonstrate enhancement at both modalities. The CT and MR imaging appearances of infantile hemangioma are similar to those of adult hemangioma. Infantile hemangioendothelioma occurs in infants under 6 months of age and is typically a larger lesion. Mesenchymal hamartoma also occurs in children, and its imaging appearance depends on the presence of stromal elements and the protein content of the cyst fluid. Familiarity with these imaging features can help distinguish particular disease entities.
Index Terms: Bile ducts, CT, 76.1211 • Bile ducts, MR, 76.1214 • Bile ducts, neoplasms, 76.31 • Liver neoplasms, 761.31 Liver neoplasms, CT, 761.1211 • Liver neoplasms, diagnosis, 761.1211, 761.1214 • Liver neoplasms, MR, 761.1214
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INTRODUCTION
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Benign liver tumors are fairly common and continue to present a significant diagnostic and therapeutic challenge. At routine imaging studies, benign masses could be mistaken for primary malignant neoplasms or metastases, resulting in unnecessary surgery or incorrect cancer staging.
Most of the recent radiology literature concerning the liver has focused on lesion detection or identification of specific features (eg, enhancement patterns) that may help distinguish benign from malignant hepatic tumors. Except for hemangioma and focal nodular hyperplasia (FNH), little is known about imaging characteristics that can help identify and distinguish among the many less common benign liver masses.
In this article, we review a wide spectrum of benign hepatic tumors and present their cross-sectional imaging characteristics. In addition, we discuss optimization of examination techniques and protocols for both computed tomography (CT) and magnetic resonance (MR) imaging, including a discussion of newer applications such as CT angiography and contrast material–enhanced MR imaging of the liver. We emphasize key differential diagnostic criteria for each of the benign hepatic masses.
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CT TECHNIQUE
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Spiral CT is currently the imaging modality of choice for evaluation of the liver and for detection of hepatic masses. Spiral CT offers many advantages over conventional dynamic CT. First, it allows rapid subsecond scanning, thus permitting scanning during different phases (arterial, portal, delayed) of hepatic enhancement. Second, partial volume averaging in imaging of liver lesions is reduced with spiral CT because axial reconstructions can be performed at optimal intervals and overlapping reconstructions can be obtained. Third, respiratory misregistration can be eliminated when the liver is scanned during a single breath hold. Finally, spiral CT data sets form the basis for three-dimensional (3D) imaging and CT angiography.
CT Protocols
Our routine abdominal CT protocol consists of a spiral CT scan of the abdomen and pelvis after oral and intravenous administration of contrast material. Typically, 120 mL (350 mg/mL iodine) of iohexol (Omnipaque; Sterling Winthrop, New York, NY) is injected at a rate of 2–3 mL/sec. The scan delay is typically 50 seconds, with a section thickness of 5 mm and a pitch of 1.6. Reconstructions are performed at 5-mm intervals.
In cases of suspected liver disease, specific liver protocols are used depending on the clinical question. For instance, for evaluation of a possible liver mass we perform a dedicated dual-phase spiral CT scan through the liver with additional delayed scans as needed. A 3–5-mm section thickness is used, with a pitch of 1–1.5 and a 3-mm reconstruction interval. If there is a known liver mass (eg, hemangioma) requiring further identification of enhancement characteristics, sequential CT scans of the liver are obtained after the intravenous administration of contrast material. This allows close observation of the dynamic enhancement pattern of the lesion.
3D CT Angiography
If 3D evaluation of the liver vasculature is desired, positive oral contrast agents such as diatrizoate meglumine (Hypaque 3%; Nycomed, Princeton, NJ) should not be used because they can interfere with 3D visualization of abdominal vessels. The appropriate scan delay is chosen to highlight either arterial flow (25 seconds) or venous flow (60 seconds). Intravenous injection rates of 3–5 mL/sec are optimal for CT angiography. Spiral CT data sets are obtained and then transferred over an Ethernet to an Infinite Reality or Onyx workstation with Reality Engine graphics (Silicon Graphics, Mountain View, Calif) for interactive volume rendering. The 3D volume set can then be manipulated by using different orientations and cut planes and by adjusting window level and width, brightness, and opacity to optimize visualization of the tumor and liver vasculature.
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MR IMAGING TECHNIQUE
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MR imaging is an important diagnostic tool in the detection and characterization of focal liver lesions. Advantages of MR imaging include multiplanar imaging capability, superior contrast resolution, and no ionizing radiation. Faster imagers and new imaging sequences allow dynamic imaging for lesion characterization.
Contrast Agents
Until recently, gadolinium chelates were the only MR imaging contrast agents approved by the U.S. Food and Drug Administration. Recently, however, other agents have been approved for hepatobiliary imaging.
Superparamagnetic Iron Oxides.—Superparamagnetic iron oxides are small iron particles that are taken up by the reticuloendothelial system, resulting in normal liver having decreased signal intensity on T2-weighted MR images (1,2). Currently, ferumoxides are used in an attempt to improve detection of metastases to the liver. Metastases do not have reticuloendothelial cells and do not take up the contrast material; consequently, they appear hyperintense relative to normal liver parenchyma on T2-weighted MR images (Fig 1).
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Figure 1a. Metastases to the liver in a 67-year-old man with colon cancer. (a) Unenhanced fast spin-echo T2-weighted (repetition time msec/echo time msec = 5,000/104) MR image demonstrates a 1.5-cm metastasis (curved arrow) in the posterior segment of the right hepatic lobe and a 3-cm cyst (straight arrow) in the left lobe. (b) Fast spin-echo T2-weighted (5,000/104) MR image obtained after administration of ferumoxide (Feridex; Advanced Magnetics, Cambridge, Mass) shows the normal liver and spleen with diffuse decreased signal intensity (cf a). The cyst (straight arrow) and the metastasis (curved arrow) do not take up the contrast agent and appear hyperintense.
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Figure 1b. Metastases to the liver in a 67-year-old man with colon cancer. (a) Unenhanced fast spin-echo T2-weighted (repetition time msec/echo time msec = 5,000/104) MR image demonstrates a 1.5-cm metastasis (curved arrow) in the posterior segment of the right hepatic lobe and a 3-cm cyst (straight arrow) in the left lobe. (b) Fast spin-echo T2-weighted (5,000/104) MR image obtained after administration of ferumoxide (Feridex; Advanced Magnetics, Cambridge, Mass) shows the normal liver and spleen with diffuse decreased signal intensity (cf a). The cyst (straight arrow) and the metastasis (curved arrow) do not take up the contrast agent and appear hyperintense.
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Although there have been some reports of benign hepatic tumors being visualized with ferumoxides, large-scale studies have not been conducted (3). Theoretically, benign tumors with functioning Kupffer cells (FNH, hepatocellular adenoma) should take up the contrast material (1). One study found that although there was accumulation of contrast material in FNH and adenoma, the tumors generally showed less signal intensity loss than normal liver and therefore had slightly higher signal intensity (3).
Other benign lesions without Kupffer cells (eg, cysts, cystadenomas, bile duct adenomas) do not take up the contrast material and therefore appear hyperintense relative to normal liver on contrast-enhanced T2-weighted MR images (Fig 1). For hemangiomas, the predominant effect of ferumoxides appears to be due to residual contrast material in the blood pool. Hemangiomas may have increased signal intensity on contrast-enhanced T1-weighted MR images but have decreased signal intensity on contrast-enhanced T2-weighted images relative to unenhanced T2-weighted images (4). More studies are needed to determine the role of ferumoxides in the evaluation of other benign tumors.
Mangafodipir Trisodium.—A more recently developed paramagnetic agent, mangafodipir trisodium (Teslascan; Nycomed, Princeton, NJ), has been approved by the U.S. Food and Drug Administration for use in MR imaging of the liver. This agent is taken up by hepatocytes and shortens T1 relaxation time, leading to increased signal intensity in normal liver parenchyma on T1-weighted MR images. The use of mangafodipir trisodium is being studied as a means of improving the detection of liver metastases that do not take up the agent and therefore appear hypointense relative to normal liver on contrast-enhanced T1-weighted MR images. Its use in the detection or characterization of benign hepatic tumors has not been investigated. However, benign tumors that are hepatocellular in origin (eg, FNH) are expected to take up the agent and show T1 shortening (Fig 2).
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Figure 2a. FNH. (a) Unenhanced fast multiplanar spoiled gradient-echo (FMPSPGR) (110/4.2) MR image demonstrates a slightly hypointense, 8 x 6-cm mass in the right lobe of the liver (arrows). (b) Unenhanced fast spin-echo (5,454/105) MR image demonstrates the mass (arrows) with signal intensity characteristics similar to those of normal liver. A small central scar with high signal intensity is also seen. (c) FMPSPGR (170/4.2) MR image obtained after the administration of mangafodipir trisodium demonstrates increased signal intensity within the liver due to uptake of the agent by hepatocytes. The mass (arrows) shows increased signal intensity because FNH contains hepatocytes. The central scar now has decreased signal intensity.
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Figure 2b. FNH. (a) Unenhanced fast multiplanar spoiled gradient-echo (FMPSPGR) (110/4.2) MR image demonstrates a slightly hypointense, 8 x 6-cm mass in the right lobe of the liver (arrows). (b) Unenhanced fast spin-echo (5,454/105) MR image demonstrates the mass (arrows) with signal intensity characteristics similar to those of normal liver. A small central scar with high signal intensity is also seen. (c) FMPSPGR (170/4.2) MR image obtained after the administration of mangafodipir trisodium demonstrates increased signal intensity within the liver due to uptake of the agent by hepatocytes. The mass (arrows) shows increased signal intensity because FNH contains hepatocytes. The central scar now has decreased signal intensity.
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Figure 2c. FNH. (a) Unenhanced fast multiplanar spoiled gradient-echo (FMPSPGR) (110/4.2) MR image demonstrates a slightly hypointense, 8 x 6-cm mass in the right lobe of the liver (arrows). (b) Unenhanced fast spin-echo (5,454/105) MR image demonstrates the mass (arrows) with signal intensity characteristics similar to those of normal liver. A small central scar with high signal intensity is also seen. (c) FMPSPGR (170/4.2) MR image obtained after the administration of mangafodipir trisodium demonstrates increased signal intensity within the liver due to uptake of the agent by hepatocytes. The mass (arrows) shows increased signal intensity because FNH contains hepatocytes. The central scar now has decreased signal intensity.
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MR Imaging Protocols
Our protocol for routine abdominal MR imaging consists of axial spin-echo T1-weighted and fast spin-echo T2-weighted MR images through the abdomen and pelvis. Typically, an 8-mm section thickness with a 2-mm gap is used for abdominal images and a 10-mm section thickness with a 2-mm gap is used for pelvic images. Additional imaging planes are used if necessary.
If liver disease is suspected, specific liver protocols are used depending on the clinical question. For instance, for better characterization of a known liver mass, a variety of MR imaging sequences (FMPSPGR, fast spin-echo T2-weighted, fast-inversion-recovery, gradient-recalled acquisition in a steady state) are performed through the liver with use of a torso coil. In addition, axial FMPSPGR MR images are obtained through the liver following injection of 10–20 mL of gadopentetate dimeglumine (Magnevist; Berlex, Wayne, NJ).
For better characterization of enhancement patterns in a known liver mass, 10–20 mL of gadopentetate dimeglumine is injected at a rate of 1–2 mL/sec through a catheter placed in a peripheral vein. Sequential FMPSPGR MR images are obtained through the lesion at 30 seconds and 60 seconds after injection, then every 60 seconds for 5 minutes (or longer if necessary).
For studies performed with ferumoxides, images should be obtained within 3 hours after contrast material administration. At our institution, unenhanced FMPSPGR and fast spin-echo T2-weighted MR images are obtained. After being diluted in 100 mL of water with 5% dextrose, a ferumoxide is administered over 30 minutes by a nurse and contrast-enhanced axial FMPSPGR and fast spin-echo T2-weighted sequences are performed.
For studies performed with mangafodipir trisodium, patients should be imaged within 10–15 minutes after contrast material administration. At our institution, unenhanced FMPSPGR MR images (with and without fat saturation) are obtained as well as unenhanced fast spin-echo T2-weighted MR images of the liver. Mangafodipir trisodium is then administered slowly over 3 minutes, and contrast-enhanced FMPSPGR MR images (with and without fat saturation) are obtained. High-resolution imaging (256 x 192 matrix) is used. With gadopentetate dimeglumine, the entire liver must be imaged during a single breath hold, and therefore only a 256 x 128 matrix can be used. With mangafodipir trisodium–enhanced early-phase and delayed images, increased imaging time can be used to decrease pixel size (and increase resolution) because imaging is performed under steady-state conditions.
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BENIGN LIVER TUMORS
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Hepatic Cysts
Hepatic cysts are common benign liver lesions that occur in 2%–7% of the population. These lesions may be isolated or multiple and vary from a few millimeters to several centimeters in diameter. Hepatic cysts are typically discovered incidentally and have no malignant potential. Certain diseases such as polycystic liver disease and polycystic kidney disease are associated with multiple hepatic cysts.
At CT, a hepatic cyst demonstrates water attenuation (0–10 HU). The wall is usually imperceptible, and the cyst does not enhance after intravenous administration of contrast material (Figs 3, 4). Similarly, at MR imaging a hepatic cyst is isointense relative to water (Fig 5) and does not enhance after administration of gadopentetate dimeglumine.
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Figure 3a. Hepatic cyst. Illustrations demonstrate the appearance of a liver cyst at contrast-enhanced spiral CT during the arterial phase (a), portal phase (b), and delayed phase (c). The liver parenchyma enhances, but the cyst does not. The walls of the cyst are imperceptible.
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Figure 3b. Hepatic cyst. Illustrations demonstrate the appearance of a liver cyst at contrast-enhanced spiral CT during the arterial phase (a), portal phase (b), and delayed phase (c). The liver parenchyma enhances, but the cyst does not. The walls of the cyst are imperceptible.
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Figure 3c. Hepatic cyst. Illustrations demonstrate the appearance of a liver cyst at contrast-enhanced spiral CT during the arterial phase (a), portal phase (b), and delayed phase (c). The liver parenchyma enhances, but the cyst does not. The walls of the cyst are imperceptible.
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Figure 4. Hepatic cyst. Contrast-enhanced spiral CT scan reveals a large cyst with water attenuation in the right hepatic lobe (arrows). The cyst is unenhanced with imperceptible walls.
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Hemangioma
Hemangioma is the most common benign liver tumor and is seen at autopsy in up to 7% of cases. Hemangiomas usually occur in women and are typically asymptomatic, incidental findings. Although hemangiomas can occur at any age, they are rarely diagnosed until adulthood. They may be isolated or multiple and often occur in the posterior segment of the right hepatic lobe (5,6). Hemangiomas are usually less than 5 cm in diameter but can be very large. They typically remain stable in size but may demonstrate growth (7).
Pathologically, hemangiomas are composed of many endothelium-lined vascular spaces separated by fibrous septa. They derive their blood supply from the hepatic artery.
At unenhanced CT, a hemangioma is hypoattenuating and well defined; at contrast-enhanced CT, it exhibits a characteristic pattern of enhancement (8,9). The tumor demonstrates nodular peripheral puddling of contrast material on early-phase images and subsequently fills in from the periphery (Figs 6–8). A central scar (if present) may not enhance, even on delayed images. Calcification within hemangiomas has been reported, although in our experience this is not common (<5% of cases).
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Figure 6a. Hemangioma. Illustrations demonstrate the appearance of a hemangioma at contrast-enhanced spiral CT during the arterial phase (a), portal phase (b), and delayed phase (c). Peripheral puddling of contrast material is characteristic of hemangiomas on early-phase images. The hemangioma subsequently fills in from the periphery. On delayed images, the mass may fill in completely and be isoattenuating or slightly hyperattenuating. Hemangiomas may not enhance completely if they are large or have a central scar.
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Figure 6b. Hemangioma. Illustrations demonstrate the appearance of a hemangioma at contrast-enhanced spiral CT during the arterial phase (a), portal phase (b), and delayed phase (c). Peripheral puddling of contrast material is characteristic of hemangiomas on early-phase images. The hemangioma subsequently fills in from the periphery. On delayed images, the mass may fill in completely and be isoattenuating or slightly hyperattenuating. Hemangiomas may not enhance completely if they are large or have a central scar.
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Figure 6c. Hemangioma. Illustrations demonstrate the appearance of a hemangioma at contrast-enhanced spiral CT during the arterial phase (a), portal phase (b), and delayed phase (c). Peripheral puddling of contrast material is characteristic of hemangiomas on early-phase images. The hemangioma subsequently fills in from the periphery. On delayed images, the mass may fill in completely and be isoattenuating or slightly hyperattenuating. Hemangiomas may not enhance completely if they are large or have a central scar.
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Figure 8a. Figures 7, 8. Hemangioma. (7a) Contrast-enhanced spiral CT scan obtained during the arterial phase demonstrates a 3-cm, low-attenuation mass in the anterior segment of the right hepatic lobe (arrows). Note the characteristic peripheral nodular puddling of contrast material. (7b) Delayed CT scan obtained at the same level demonstrates complete enhancement of the mass (arrows), which now appears slightly hyperattenuating due to delayed washout of contrast material. (8a) Contrast-enhanced spiral CT scan obtained during the arterial phase demonstrates an 8.5-cm mass in the left hepatic lobe (arrows). Characteristic puddling of contrast material is seen (cf Fig 7a). (8b) CT scan obtained at the same level during the portal phase demonstrates progressive enhancement of the lesion (arrows).
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Figure 8b. Figures 7, 8. Hemangioma. (7a) Contrast-enhanced spiral CT scan obtained during the arterial phase demonstrates a 3-cm, low-attenuation mass in the anterior segment of the right hepatic lobe (arrows). Note the characteristic peripheral nodular puddling of contrast material. (7b) Delayed CT scan obtained at the same level demonstrates complete enhancement of the mass (arrows), which now appears slightly hyperattenuating due to delayed washout of contrast material. (8a) Contrast-enhanced spiral CT scan obtained during the arterial phase demonstrates an 8.5-cm mass in the left hepatic lobe (arrows). Characteristic puddling of contrast material is seen (cf Fig 7a). (8b) CT scan obtained at the same level during the portal phase demonstrates progressive enhancement of the lesion (arrows).
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At MR imaging, hemangiomas usually appear hypointense and well defined on T1-weighted images and demonstrate a marked hyperintensity that increases with echo time on T2-weighted images (Fig 9) (5,10). After administration of gadopentetate dimeglumine, a hemangioma demonstrates the same characteristic pattern of enhancement as is seen at CT (Fig 10).
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Figure 9a. Hemangioma. T1-weighted (600/20) (a) and T2-weighted (2,500/60, 2,500/120) (b, c) MR images demonstrate the typical appearance of a liver hemangioma (arrow). Hemangiomas appear hyperintense on T2-weighted MR images with increasing echo time. b.
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Figure 9b. Hemangioma. T1-weighted (600/20) (a) and T2-weighted (2,500/60, 2,500/120) (b, c) MR images demonstrate the typical appearance of a liver hemangioma (arrow). Hemangiomas appear hyperintense on T2-weighted MR images with increasing echo time. b.
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Figure 9c. Hemangioma. T1-weighted (600/20) (a) and T2-weighted (2,500/60, 2,500/120) (b, c) MR images demonstrate the typical appearance of a liver hemangioma (arrow). Hemangiomas appear hyperintense on T2-weighted MR images with increasing echo time. b.
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Figure 10a. Hemangioma. Dynamic T1-weighted (600/15) MR images demonstrate the classic enhancement pattern of a liver hemangioma (arrows). The hemangioma demonstrates early peripheral puddling of contrast material (a), then fills in from the periphery (b). The central area does not enhance due to a central scar.
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Figure 10b. Hemangioma. Dynamic T1-weighted (600/15) MR images demonstrate the classic enhancement pattern of a liver hemangioma (arrows). The hemangioma demonstrates early peripheral puddling of contrast material (a), then fills in from the periphery (b). The central area does not enhance due to a central scar.
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Focal Nodular Hyperplasia
FNH is the second most common benign neoplasm of the liver after hemangioma. It typically occurs in young women and is usually discovered incidentally, although some patients may present with right upper quadrant pain (11). As with hepatic adenomas, there is an increased prevalence of FNH in women taking oral contraceptives (12).
FNH is thought to represent a benign hyperplastic response of the liver to a congenital arteriovenous malformation and is composed of hepatocytes, Kupffer cells, primitive bile ductules not connected with the biliary tree, and blood vessels (11). The mass is usually less than 5 cm in diameter and is often located near the liver surface. A central fibrous scar containing a small arteriovenous malformation may be present. Although FNH is highly vascular, it is unlikely to result in hemorrhage. FNH has no malignant potential, and multiple lesions may be seen at the time of presentation.
At unenhanced CT, FNH usually appears homogeneous, well defined, and hypoattenuating or isoattenuating relative to the liver; at contrast-enhanced CT, it exhibits a characteristic pattern of enhancement (6). FNH enhances brightly on early-phase images, and the contrast material subsequently washes out. On delayed scans, the mass may be isoattenuating relative to the liver and therefore imperceptible except for any mass effect. A central scar (if present) may demonstrate delayed enhancement and may remain bright on subsequent images due to delayed washout (Figs 11–13).
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Figure 11a. FNH. Illustrations demonstrate the appearance of FNH at contrast-enhanced spiral CT during the arterial phase (a), portal phase (b), and delayed phase (c). The mass enhances brightly during the arterial phase and may be completely isoattenuating on delayed scans. A central scar (if present) may demonstrate delayed enhancement that persists due to slow washout.
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Figure 11b. FNH. Illustrations demonstrate the appearance of FNH at contrast-enhanced spiral CT during the arterial phase (a), portal phase (b), and delayed phase (c). The mass enhances brightly during the arterial phase and may be completely isoattenuating on delayed scans. A central scar (if present) may demonstrate delayed enhancement that persists due to slow washout.
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Figure 11c. FNH. Illustrations demonstrate the appearance of FNH at contrast-enhanced spiral CT during the arterial phase (a), portal phase (b), and delayed phase (c). The mass enhances brightly during the arterial phase and may be completely isoattenuating on delayed scans. A central scar (if present) may demonstrate delayed enhancement that persists due to slow washout.
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Figure 13a. Figures 12, 13. FNH. (12) Contrast-enhanced spiral CT scans demonstrate the characteristic enhancement pattern of FNH (solid arrows) in the arterial phase (a), portal phase (b), and delayed phase (c). Notice that the mass enhances dramatically early but is nearly imperceptible on the delayed scan. There is also a small, nonenhancing central scar (open arrow). (13a) Early-phase contrast-enhanced spiral CT scan demonstrates an 8-cm, isoattenuating hepatic mass (solid arrows) displacing adjacent vessels. A hypoattenuating central scar is also seen (open arrow). (13b) On a delayed CT scan obtained at the same level, the mass (solid arrows) is almost imperceptible except for persistent enhancement of the central scar (open arrow).
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Figure 13b. Figures 12, 13. FNH. (12) Contrast-enhanced spiral CT scans demonstrate the characteristic enhancement pattern of FNH (solid arrows) in the arterial phase (a), portal phase (b), and delayed phase (c). Notice that the mass enhances dramatically early but is nearly imperceptible on the delayed scan. There is also a small, nonenhancing central scar (open arrow). (13a) Early-phase contrast-enhanced spiral CT scan demonstrates an 8-cm, isoattenuating hepatic mass (solid arrows) displacing adjacent vessels. A hypoattenuating central scar is also seen (open arrow). (13b) On a delayed CT scan obtained at the same level, the mass (solid arrows) is almost imperceptible except for persistent enhancement of the central scar (open arrow).
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At MR imaging, FNH is isointense relative to normal liver and demonstrates early arterial enhancement after administration of gadopentetate dimeglumine (Fig 14) (12). However, the central scar may appear hypointense on T1-weighted images and hyperintense on T2-weighted images.
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Figure 14a. Classic appearance of FNH. (a, b) Unenhanced T1-weighted (198/4.2) (a) and T2-weighted (4,500/85) (b) MR images show a lesion (arrow) with signal intensity characteristics similar to those of normal liver. (c, d) Contrast-enhanced T1-weighted (198/4.2) MR images show the lesion (arrow) enhancing brightly during the arterial phase (c), then once again becoming indistinguishable from normal liver during the delayed phase (d).
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Figure 14b. Classic appearance of FNH. (a, b) Unenhanced T1-weighted (198/4.2) (a) and T2-weighted (4,500/85) (b) MR images show a lesion (arrow) with signal intensity characteristics similar to those of normal liver. (c, d) Contrast-enhanced T1-weighted (198/4.2) MR images show the lesion (arrow) enhancing brightly during the arterial phase (c), then once again becoming indistinguishable from normal liver during the delayed phase (d).
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Figure 14c. Classic appearance of FNH. (a, b) Unenhanced T1-weighted (198/4.2) (a) and T2-weighted (4,500/85) (b) MR images show a lesion (arrow) with signal intensity characteristics similar to those of normal liver. (c, d) Contrast-enhanced T1-weighted (198/4.2) MR images show the lesion (arrow) enhancing brightly during the arterial phase (c), then once again becoming indistinguishable from normal liver during the delayed phase (d).
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Figure 14d. Classic appearance of FNH. (a, b) Unenhanced T1-weighted (198/4.2) (a) and T2-weighted (4,500/85) (b) MR images show a lesion (arrow) with signal intensity characteristics similar to those of normal liver. (c, d) Contrast-enhanced T1-weighted (198/4.2) MR images show the lesion (arrow) enhancing brightly during the arterial phase (c), then once again becoming indistinguishable from normal liver during the delayed phase (d).
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Hepatic Adenoma
Hepatic adenoma occurs almost exclusively in young women taking oral contraceptives. Occasionally, however, it is seen in men who use anabolic steroids or in patients with glycogen storage disease.
Patients present with hepatomegaly or acute onset of right upper quadrant pain due to intratumoral hemorrhage. Adenomas can regress after discontinuation of oral contraceptives, although some adenomas will continue to grow and bleed. In addition, malignant transformation is seen on rare occasions (13). Thus, because of the risk of rupture or malignant transformation, hepatic adenomas are surgically removed.
Hepatic adenomas are typically 5–10 cm in diameter. They are surrounded by a capsule and do not have the normal hepatic architecture, being composed of benign hepatocytes arranged in sheets and cords. Areas of hemorrhage and infarction are often seen within the tumor.
At CT, hepatic adenomas appear as a well-defined, hypoattenuating mass. The presence of hemorrhage and heterogeneous attenuation is usually the key to correct identification (6). The borders are well defined because of the surrounding capsule. Moreover, because hepatic adenomas are supplied by the hepatic artery, they exhibit early enhancement and may appear isoattenuating relative to the liver on delayed scans (Figs 15–17a). The MR imaging appearance of hepatic adenomas also varies depending on the presence of hemorrhage (Fig 17b).
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Figure 15a. Hepatic adenoma. Illustrations demonstrate the appearance of a hepatic adenoma at contrast-enhanced spiral CT during the arterial phase (a), portal phase (b), and delayed phase (c). Overall, the enhancement pattern is similar to that of FNH. However, many hepatic adenomas have a more complex appearance due to the presence of acute or chronic hemorrhage.
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Figure 15b. Hepatic adenoma. Illustrations demonstrate the appearance of a hepatic adenoma at contrast-enhanced spiral CT during the arterial phase (a), portal phase (b), and delayed phase (c). Overall, the enhancement pattern is similar to that of FNH. However, many hepatic adenomas have a more complex appearance due to the presence of acute or chronic hemorrhage.
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Figure 15c. Hepatic adenoma. Illustrations demonstrate the appearance of a hepatic adenoma at contrast-enhanced spiral CT during the arterial phase (a), portal phase (b), and delayed phase (c). Overall, the enhancement pattern is similar to that of FNH. However, many hepatic adenomas have a more complex appearance due to the presence of acute or chronic hemorrhage.
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Figure 17a. Hepatic adenoma. (a) Contrast-enhanced CT scan demonstrates an ill-defined, heterogeneously enhanced liver mass (arrows) with a central area of low attenuation. (b) T2-weighted MR image demonstrates high signal intensity within the mass as well as small, nodular satellite lesions. At surgery, a hepatic adenoma with hemorrhage was diagnosed.
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Figure 17b. Hepatic adenoma. (a) Contrast-enhanced CT scan demonstrates an ill-defined, heterogeneously enhanced liver mass (arrows) with a central area of low attenuation. (b) T2-weighted MR image demonstrates high signal intensity within the mass as well as small, nodular satellite lesions. At surgery, a hepatic adenoma with hemorrhage was diagnosed.
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Infantile Hemangioendothelioma
Infantile hemangioendothelioma is a benign but aggressive liver tumor that usually manifests in infants less than 6 months old who present with hepatomegaly or an abdominal mass (14). Congestive heart failure, bleeding, anemia, thrombocytopenia, or cutaneous hemangioma may also be present. Although hemangioendothelioma is a benign tumor that typically resolves spontaneously, children may die of complications such as severe heart failure (14). Malignant transformation into angiosarcoma has been reported but is rare (15,16).
Pathologically, infantile hemangioendothelioma is composed of a network of connecting vascular channels lined by endothelial cells (14). It is typically a large (1–20-cm), solitary mass but may be multifocal.
At unenhanced CT, infantile hemangioendothelioma usually appears as a large, well-defined, hypoattenuating mass. Up to 16% of these masses demonstrate calcification, and hemorrhage is not uncommon (17). After intravenous administration of contrast material, the enhancement pattern may resemble that of a hemangioma (Figs 18, 19). Multifocal lesions are usually small, frequently enhance completely, and typically do not demonstrate hemorrhage or necrosis. This appearance may be mistaken for metastases (14).
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Figure 18a. Hemangioendothelioma. Illustrations demonstrate the appearance of an infantile hemangioendothelioma at contrast-enhanced spiral CT during the arterial phase (a), portal phase (b), and delayed phase (c). These tumors are usually large and demonstrate an enhancement pattern similar to that of hemangiomas, but they occur in young children.
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Figure 18b. Hemangioendothelioma. Illustrations demonstrate the appearance of an infantile hemangioendothelioma at contrast-enhanced spiral CT during the arterial phase (a), portal phase (b), and delayed phase (c). These tumors are usually large and demonstrate an enhancement pattern similar to that of hemangiomas, but they occur in young children.
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Figure 18c. Hemangioendothelioma. Illustrations demonstrate the appearance of an infantile hemangioendothelioma at contrast-enhanced spiral CT during the arterial phase (a), portal phase (b), and delayed phase (c). These tumors are usually large and demonstrate an enhancement pattern similar to that of hemangiomas, but they occur in young children.
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Figure 19a. Hemangioendothelioma in a neonate with congestive heart failure. (a) Early-phase contrast-enhanced CT scan demonstrates a 20-cm hemangioendothelioma with peripheral lobular areas of intense enhancement. (b) Delayed CT scan shows inhomogeneous enhancement of the mass.
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Figure 19b. Hemangioendothelioma in a neonate with congestive heart failure. (a) Early-phase contrast-enhanced CT scan demonstrates a 20-cm hemangioendothelioma with peripheral lobular areas of intense enhancement. (b) Delayed CT scan shows inhomogeneous enhancement of the mass.
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Mesenchymal Hamartoma
Mesenchymal hamartoma is a rare, benign liver neoplasm that probably represents a congenital malformation. It usually occurs in children under 2 years of age and is slightly more common in boys. Patients typically present with an asymptomatic abdominal mass (18). To our knowledge, malignant transformation has not been reported. Treatment consists of surgical resection.
Pathologically, mesenchymal hamartoma is a large mass measuring 12–15 cm in diameter. It is composed of loose edematous tissue, blood vessels, small groups of hepatocytes, and bile ducts (19).
At unenhanced CT, mesenchymal hamartoma usually has a heterogeneous appearance. The stromal elements appear hypoattenuating, whereas the cystic component has water attenuation (19). The appearance of the mass depends on whether it is predominantly stromal (mesenchymal) or cystic. Hemorrhage occasionally occurs but is not typical. After intravenous administration of contrast material, the stromal component enhances (Figs 20, 21). The MR imaging appearance of mesenchymal hamartoma varies depending on the presence of stromal elements and the protein content of the fluid (Fig 21).
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Figure 20a. Mesenchymal hamartoma. Illustrations demonstrate the appearance of a mesenchymal hamartoma at contrast-enhanced spiral CT during the arterial phase (a), portal phase (b), and delayed phase (c). These tumors are typically large and have a complex cystic or solid imaging appearance that varies depending on the amount of stromal tissue present. It is these stromal elements that enhance.
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Figure 20b. Mesenchymal hamartoma. Illustrations demonstrate the appearance of a mesenchymal hamartoma at contrast-enhanced spiral CT during the arterial phase (a), portal phase (b), and delayed phase (c). These tumors are typically large and have a complex cystic or solid imaging appearance that varies depending on the amount of stromal tissue present. It is these stromal elements that enhance.
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Figure 20c. Mesenchymal hamartoma. Illustrations demonstrate the appearance of a mesenchymal hamartoma at contrast-enhanced spiral CT during the arterial phase (a), portal phase (b), and delayed phase (c). These tumors are typically large and have a complex cystic or solid imaging appearance that varies depending on the amount of stromal tissue present. It is these stromal elements that enhance.
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Figure 21a. Large mesenchymal hamartoma in a young child. Contrast-enhanced CT scan (a), T1-weighted MR image (b), and T2-weighted MR image (c) show that the tumor is predominantly cystic but has a thick wall and some enhancing internal stromal components.
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Figure 21b. Large mesenchymal hamartoma in a young child. Contrast-enhanced CT scan (a), T1-weighted MR image (b), and T2-weighted MR image (c) show that the tumor is predominantly cystic but has a thick wall and some enhancing internal stromal components.
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Figure 21c. Large mesenchymal hamartoma in a young child. Contrast-enhanced CT scan (a), T1-weighted MR image (b), and T2-weighted MR image (c) show that the tumor is predominantly cystic but has a thick wall and some enhancing internal stromal components.
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Benign Lipomatous Tumors
Hepatic angiomyolipoma is a rare, benign mesenchymal tumor that may be isolated or may occur in association with tuberous sclerosis (20,21). It is usually asymptomatic and discovered incidentally.
Hepatic angiomyolipoma is composed of smooth muscle cells, fat, and proliferating blood vessels. Successful diagnosis relies on identification of intratumoral fat at imaging or fine-needle aspiration biopsy. Surgical resection is not necessary unless there is associated pain, which occasionally results from intratumoral hemorrhage.
There have also been reports of pure lipomas of the liver (22). These tumors range from a few millimeters to 13 cm in diameter. There is no risk of malignant degeneration, and because the imaging appearance of lipomas is characteristic, percutaneous biopsy or surgery is usually unnecessary.
At CT and MR imaging, simple lipomas demonstrate fat attenuation or signal intensity and do not enhance after contrast material administration (Figs 22, 23) (20,22). Angiomyolipomas usually appear as a combination of fat and soft tissue (20). The soft-tissue component may enhance with intravenous administration of contrast material (Fig 24).
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Figure 22a. Lipoma. Illustrations demonstrate the appearance of a liver lipoma at contrast-enhanced spiral CT during the arterial phase (a), portal phase (b), and delayed phase (c). Lipomas have fat attenuation and do not enhance with contrast material.
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Figure 22b. Lipoma. Illustrations demonstrate the appearance of a liver lipoma at contrast-enhanced spiral CT during the arterial phase (a), portal phase (b), and delayed phase (c). Lipomas have fat attenuation and do not enhance with contrast material.
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Figure 22c. Lipoma. Illustrations demonstrate the appearance of a liver lipoma at contrast-enhanced spiral CT during the arterial phase (a), portal phase (b), and delayed phase (c). Lipomas have fat attenuation and do not enhance with contrast material.
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Figure 23. Lipoma in a patient with tuberous sclerosis. CT scan demonstrates a 1-cm lipoma with an attenuation value of -15 HU in the right hepatic lobe (straight arrow). The patient also had an angiomyolipoma in the left kidney (curved arrows).
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Figure 24a. Angiomyolipoma. Illustrations demonstrate the appearance of a liver angiomyolipoma at contrast-enhanced spiral CT during the arterial phase (a), portal phase (b), and delayed phase (c). Angiomyolipomas are typically a mixture of fatty and mesenchymal elements. The soft-tissue components enhance, whereas the fat does not.
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Figure 24b. Angiomyolipoma. Illustrations demonstrate the appearance of a liver angiomyolipoma at contrast-enhanced spiral CT during the arterial phase (a), portal phase (b), and delayed phase (c). Ang | |
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Abstract
INTRODUCTION
