AJR 2004; 183:443-452
© American Roentgen Ray Society
Comprehensive Analysis of Hypervascular Liver Lesions Using 16-MDCT and Advanced Image Processing
Ihab R. Kamel1,
Leo P. Lawler and
Elliot K. Fishman
1 All authors: Russell H. Morgan Department of Radiology and Radiological
Sciences, Johns Hopkins Outpatient Center, 601 N Caroline St., Rm. 3235A,
Baltimore, MD 21287.
Received September 29, 2003;
accepted after revision November 6, 2003.
Address correspondence to I. R. Kamel.
Introduction
The introduction of 16-MDCT provides several advantages for detection and
analysis of hypervascular hepatic lesions, including faster scanning, improved
spatial and temporal resolution, less respiratory misregistration, better
contrast bolus capture and timing of arterial and venous phases, and
volumetric acquisition of the entire data set in a single breath-hold
[1-4].
These factors have significantly improved the image quality of MDCT,
particularly in hepatic imaging. Advancement in image postprocessing
technology has accompanied that of image acquisition. New commercially
available workstations, with efficient real-time editing, offer high-quality
image postprocessing, facilitating the analysis and interpretation of large
volumetric data sets [5].
In this pictorial essay, we provide details of our initial experience using
16-MDCT scanners in the characterization of hypervascular liver lesions. We
show the value of volumetric analysis using a 3D workstation in the detection
and characterization of these lesions.
Imaging and Postprocessing Technique
Scanning was performed using the Sensation 16 scanner (Siemens Medical
Solutions). Gantry rotation time was 500 msec, with detector collimation and
slice thickness of 0.75 mm for arterial and portal venous phase image
acquisition. Patients received 750 mL of water as a neutral contrast agent 15
min before the study began and another 250 mL at the time of the study. All
patients received 120 mL of nonionic contrast medium (iohexol [350 mg/mL],
Omnipaque, Amersham Health) injected IV at a rate of 3-4 mL/sec with a power
injector. The scan delay was 25-30 sec and 55-60 sec for arterial and portal
venous phases, respectively. All CT data, in the original resolution of 512
x 512, were sent from the scanner to a freestanding commercially
available workstation using In Space Software (Leonardo, Siemens Medical
Solutions) for postprocessing. Real-time axial scrolling, interactive
maximum-intensity-projection, and volume-rendered techniques were used to
evaluate the hepatic parenchyma. Slab maximum-intensity-projection images
obtained in a plane that avoids structures of overlapping high attenuation
allowed accurate delineation of tumor stain, neovascularity, feeding vessels,
and draining veins. Sliding maximum-intensity-projection images allowed fast
visualization of the lesion of interest, and rotation in different planes
facilitated tracing the full course of a feeding vessel, which may be
difficult to depict on axial images.
Hepatic Parenchymal Evaluation
Multiplanar volume-rendered and maximum-intensity-projection 16-MDCT data
allow robust evaluation of the hepatic parenchyma. The near-isotropic pixel
resolution provides high-quality data sets with accurate parenchymal
evaluation of the liver, independent of viewing perspective. Volume-rendered
techniques allow the user to manipulate the degree of opacity in each voxel,
depending on the specific tissue type to be displayed, and also allow true
representation of all voxel density values. The high fidelity of this
technique harnesses the original high quality of 16-MDCT data, preserves both
vascular and parenchymal detail, and allows fast imaging review in multiple
planes. The maximum-intensity-projections technique allows structures that are
not in the same plane to be visualized along their entire length; this feature
is advantageous in the case of the hepatic arteries. This technique is
particularly valuable in evaluating tumor vascularity, feeding vessels, and
draining veins.
Image review of 16-MDCT data should not be limited to the axial plane of
image acquisition. In fact, the coronal plane provides a more intuitive
understanding of the anatomy compared with the axial plane. In hypervascular
hepatic lesions, this technique has improved lesion characterization
[6] and also has allowed the
delineation of many of the vascular imaging features that are typically seen
on digital subtraction angiography
[7]. Some features that are not
well seen on the axial plane include vascular displacement, encasement or
invasion, neovascularity, tumor blush, and arteriovenous shunting. Vascular
displacement may outline masses but does not distinguish benign and malignant
lesions. Vascular encasement or invasion is a reliable sign of malignancy. The
encased artery appears serrated or serpentine and may progress to complete
occlusion. Many malignant masses and some benign lesions may develop their own
blood supply, also known as neovascularity. These tumor vessels lack normal
muscular walls and are short and serpentine with abrupt angulation and
variable diameter. On volume-rendered images, tumor vessels appear as
increased vascularity relative to the surrounding tissue; this finding is
often diagnostic of neoplasm. Contrast media accumulation in the tumor
interstitium results in a tumor blush during the parenchymal phase of
enhancement. Vascular tumors may result in arteriovenous shunting, and in such
cases, the draining veins may be seen during the arterial phase. Relative
parenchymal enhancement and irregular vessels are often seen in customized
imaging planes but may remain occult in the axial plane.
Cavernous Hemangioma
Cavernous hemangioma is the most common benign liver lesion, occurring in
5-20% of the population. On 16-MDCT, a feeding artery may be seen. Feeding
arteries are normal in caliber, regardless of tumor size, and occasionally, a
feeding portal venous branch is identified (Figs.
1A,
1B,
1C,
1D,
1E and
2). Vessels may be displaced
but not encased or invaded, and no neovascularity is seen. In the arterial
phase, small dilated amorphous vascular spaces start to opacify peripherally,
gradually filling in centrally in the portal venous phase. Using advanced
imaging processing can help identify the characteristic peripheral small foci
of early enhancement, which may be better seen in a plane other than the axial
plane of image acquisition (Figs.
1A,
1B,
1C,
1D,
1E,
2,
3A,
3B).
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Fig. 1C. —Typical hemangioma in 72-year-old woman. Coronal volume-rendered CT
image obtained in portal venous phase shows peripheral nodular enhancement
(arrow) better, confirming diagnosis of hemangioma.
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Fig. 2. —Typical hemangioma in 53-year-old woman. Coronal volume-rendered CT
image obtained in portal venous phase shows peripheral nodular enhancement.
Note small branch of left portal vein (arrow) feeding left aspect of
mass. No neovascularity or vascular invasion is noted.
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Fig. 3A. —Typical hemangioma in 58-year-old woman. Coronal
maximum-intensity-projection image obtained in arterial phase shows peripheral
nodular enhancement (arrow) in large caudate lobe hemangioma. Coronal
plane shows lesion extent and enhancement better than conventional axial
plane.
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Fig. 3B. —Typical hemangioma in 58-year-old woman. Coronal volume-rendered CT
image obtained in portal venous phase shows increasing nodular enhancement
(straight arrow). Note displacement of right hepatic vein (curved
arrow), without vascular invasion.
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Focal Nodular Hyperplasia
Focal nodular hyperplasia may occur in 2-5% of the population. It is
usually small and rarely symptomatic, although lesions may grow to more than
10 cm in diameter. Focal nodular hyperplasia is a nonencapsulated firm nodule
of normal hepatocytes with a distinct central scar and thin radiating fibrous
septa containing Kupffer's cells and primitive bile ductules. Intratumoral
calcification, fat, hemorrhage, and necrosis are extremely rare. On 16-MDCT
with volume rendering, feeding arteries can be easily identified, and these
divide into smaller penetrating branches, resulting in a reticular pattern in
the center of the mass (Figs.
4A,
4B and
5A,
5B). Sliding
maximum-intensity-projection images may help identify intratumoral vessels
[8]. Homogeneous
hyperenhancement is noted in the arterial phase, and this washes out in the
portal venous phase. No arterial dilatation or neovascularity is seen. A
central scar may be seen in large lesions (Figs.
4A,
4B and
5A,
5B) and may be better
visualized in a plane other than the axial plane of acquisition.
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Fig. 4A. —Focal nodular hyperplasia in 28-year-old woman. Coronal
maximum-intensity-projection image obtained in arterial phase shows mass with
reticular pattern of enhancement (arrow). Mass was isodense to liver
on portal venous phase.
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Fig. 5A. —Focal nodular hyperplasia in 28-year-old woman. Coronal
maximum-intensity-projection image obtained in arterial phase reveals mass in
right lobe with diffuse reticular enhancement. Note feeding artery
(straight arrow) in inferior aspect of mass and streak artifacts
(curved arrow) from cholecystectomy clips.
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Fig. 5B. —Focal nodular hyperplasia in 28-year-old woman. Coronal
volume-rendered CT image obtained in portal venous phase reveals central scar
(straight arrow) and vascular displacement (curved arrow).
Mass is isodense to hepatic parenchyma.
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Hepatocellular Carcinoma
The most common primary hepatic neoplasm is hepatocellular carcinoma. Its
incidence is rising in the United States and has almost doubled over the past
20 years. This rise is caused in part by the epidemic of hepatitis C virus,
which can lead to both cirrhosis and subsequent development of hepatocellular
carcinoma. Sixteen-MDCT with volume rendering shows enlargement of the feeding
hepatic artery and neovascularity (Figs.
6A,
6B,
7,
8A,
8B). Some lesions may show
arterial to portal venous shunting. Venous invasion is characteristic of
hepatocellular carcinoma and is rare in other neoplasms and metastases (Fig.
9A,
9B). Volume rendering allows
the detection of subtle lesions that may be difficult to detect on axial
images, particularly in cirrhotic livers with heterogeneous parenchyma (Fig.
10A,
10B).
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Fig. 6A. —Hepatocellular carcinoma in 48-year-old man with history of
hepatitis C. Coronal maximum-intensity-projection image obtained in arterial
phase reveals two small hypervascular nodules in right lobe, with small
arterial feeder vessels (arrows) from anterior branch of right
hepatic artery. These vessels fail to taper toward periphery of liver and
terminate abruptly in masses. These findings are difficult to detect on axial
images.
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Fig. 6B. —Hepatocellular carcinoma in 48-year-old man with history of
hepatitis C. Coronal volume-rendered CT image obtained in portal venous phase
reveals persistent tumor stain and pooling of contrast material
(arrow).
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Fig. 7. —Hepatocellular carcinoma in 49-year-old man with history of
hepatitis C and cirrhosis. Coronal maximum-intensity-projection image obtained
in arterial phase reveals encasement of left hepatic artery, which appears
serpentine. Contrast media accumulation in tumor interstitium results in tumor
blush or stain (straight arrow). This appearance is highly suspicious
of malignancy and is easier to detect on maximum-intensity-projection images
compared with axial source images. Note replaced right hepatic artery
(curved arrow).
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Fig. 8A. —Hepatocellular carcinoma in 59-year-old woman with history of
hepatitis C and cirrhosis. Coronal maximum-intensity-projection image obtained
in arterial phase reveals serpentine arteries (straight arrow) and
feeding mass (curved arrow) in right lobe. Note heterogeneous liver
parenchyma due to cirrhosis.
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Fig. 8B. —Hepatocellular carcinoma in 59-year-old woman with history of
hepatitis C and cirrhosis. Coronal volume-rendered CT image obtained in portal
venous phase reveals mass with surrounding low attenuation (arrow)
due to capsule.
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Fig. 9A. —Multifocal hepatocellular carcinoma in 76-year-old man with history
of cirrhosis. Coronal maximum-intensity-projection image obtained in arterial
phase reveals numerous nodules, with largest (straight arrow) located
in left lobe. Multiple feeding arteries (curved arrows) are
identified, particularly to left lobe mass.
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Fig. 9B. —Multifocal hepatocellular carcinoma in 76-year-old man with history
of cirrhosis. Coronal volume-rendered CT image obtained in portal venous phase
reveals clots in portal vein (straight arrow) and inferior vena cava
(curved arrow).
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Fig. 10A. —Recurrent hepatocellular carcinoma in 70-year-old man with history
of cirrhosis and prior left hepatectomy. Axial CT image obtained in arterial
phase reveals subtle mass (arrow) in inferior right lobe.
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Fig. 10B. —Recurrent hepatocellular carcinoma in 70-year-old man with history
of cirrhosis and prior left hepatectomy. Coronal volume-rendered CT image
shows improved conspicuity of mass (arrow), likely due to different
manipulation of brightness and contrast values.
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Hypervascular Metastases
Hypervascular metastases are those with an abundant blood supply, typically
greater than that of the normal liver. These tumors include choriocarcinoma,
renal cell carcinoma, thyroid carcinoma, carcinoid tumor, and islet cell
tumor. These metastases are often multiple, and tumor burden can be easily
evaluated on 16-MDCT with volume rendering (Figs.
11A,
11B and
12A,
12B,
12C,
12D,
12E). Pooling of contrast
material may occur during the arterial phase, resulting in tumor blush.
Neovascularity may also be observed.
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Fig. 11A. —Diffuse hepatic metastases in 60-year-old woman with neuroendocrine
tumor. Coronal volume-rendered CT image obtained in arterial phase reveals
numerous nodules (arrows) with tumor stain.
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Fig. 11B. —Diffuse hepatic metastases in 60-year-old woman with neuroendocrine
tumor. Coronal volume-rendered CT image obtained in same plane as A but
with increased opacity shows additional tumors (straight arrows) and
feeding artery (curved arrow).
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Fig. 12A. —Large hepatic metastases in 39-year-old woman with neuroendocrine
tumor of pancreas. Maximum-intensity-projection image obtained in coronal
plane of arterial phase reveals two large hypervascular masses (solid
straight arrows) in right lobe, with feeding artery (curved
arrow) and arteriovenous shunting resulting in early opacification
(open arrows) of hepatic veins.
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Fig. 12B. —Large hepatic metastases in 39-year-old woman with neuroendocrine
tumor of pancreas. Maximum-intensity-projection image obtained in coronal
oblique plane of arterial phase shows feeding artery (arrow)
better.
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Fig. 12C. —Large hepatic metastases in 39-year-old woman with neuroendocrine
tumor of pancreas. Maximum-intensity-projection image obtained in axial plane
of arterial phase shows early venous drainage (arrows) better.
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Fig. 12D. —Large hepatic metastases in 39-year-old woman with neuroendocrine
tumor of pancreas. Coronal maximum-intensity-projection image obtained during
portal venous phase reveals prominent draining hepatic veins
(arrows).
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Fig. 12E. —Large hepatic metastases in 39-year-old woman with neuroendocrine
tumor of pancreas. Coronal volume-rendered CT image obtained during portal
venous phase shows pooling of contrast material (arrow) in tumor.
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Conclusion
Sixteen-MDCT allows robust evaluation of the hepatic parenchyma, with the
potential for improved detection and characterization of focal liver lesions.
Routine 3D data evaluation and interpretation offer faster and more thorough
assessment of the liver parenchyma than is possible with axial images alone. A
new paradigm in hepatic imaging is true volumetric acquisition and
display.
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Introduction
Imaging and Postprocessing...
