Dr. Khatri is an Assistant Professor of Radiology,
Body/Body MRI Section, and Dr. Pedrosa is Chief-of-MRI, Associate
Professor of Radiology, Department of Radiology, University of Texas
Southwestern Medical Center, Advanced Imaging Research Center, Dallas,
Renal cell carcinoma (RCC) is the third most common genitourinary
tumor and seventh most common cancer in the United States. Radical or
partial nephrectomy has historically been the standard treatment;
however, given the trend towards earlier diagnosis, less invasive
treatment options are feasible in appropriate cases.1 Imaging plays a
vital role in detection of renal lesions, in assessing local stage,
providing crucial information for planning surgical resection and
predicting prognosis, thus contributing to management decision making.
Although ultrasonography and computed tomography (CT) have been used for
evaluation of renal lesions, magnetic resonance (MR) imaging offers
certain advantages over these modalities.
MR imaging possesses higher inherent contrast resolution than CT or
ultrasound. In addition, it has a high sensitivity for detecting tissue
enhancement when gadolinium is administered. It is free of known
pitfalls, such as pseudoenhancement, seen routinely on CT.2-4
MR imaging with 3.0 Tesla (3T) systems, high-density phased-array
coils, and newly developed sequences, such as multiecho Dixon (mDIXON),5
offers robust image quality and excellent spatial resolution. 3T
magnets have the advantage of higher signal-to-noise, which can be used
to yield shorter acquisition times and/or increased image resolution.2
Multiplanar imaging, homogeneous fat suppression, and dynamic
contrast-enhanced imaging are also routinely achievable on 3T MR
platforms, all of which aid in lesion detection and characterization.
Our institutional 3T renal-mass evaluation protocol is performed with
the patient supine with arms placed above his head using a 16-channel
phased-array torso coil. Each sequence is obtained as a breathhold
acquisition during patients’ end-expiration, which allows for more
reproducible anatomic co-registration.2 Breath-hold times
range from 16 to 22 seconds. Coaching prior to actual image acquisition
helps improve breath-hold consistency with resultant successful
postprocessing of the subtraction images.2 A gadolinium-based
contrast agent (GBCA) is administered to patients with baseline
estimated glomerular filtration rate (eGFR) >30 mL/min/1.73 m2
and without evidence for acute exacerbation of renal disease. The GBCA
is administered intravenously via power injector at a dose of 0.1mmol/Kg
or 0.1mL/Kg followed by a bolus of 20 mL of saline, both at an
injection rate of 2 cc/second. The protocol is detailed in Table 1.
single shot turbo spin echo (SS TSE) images provide excellent image
quality due to faster acquisition times than that of conventional
multislice echo-train imaging offering a virtual breath-hold independent
imaging strategy.2 However, breath-hold imaging or
respiratory triggering with respiratory bellows (when necessary) is
recommended to ensure proper anatomic registration of the images and
coverage. Visualization of renal lesions can be optimized by improving
the dynamic range when utilizing fat-suppression techniques.
Echo-planar with diffusion-weighted imaging
imaging (EPI) is utilized to obtain diffusion-weighted images (DWI)
that allow for detection and characterization of lesions based on degree
of restriction of water motion. The authors acquire images using
respiratory triggering and multiple b values: b0, b50, b400, b800.
Apparent diffusion coefficient (ADC) maps are generated based on the
T1-weighted images include 2-dimensional (2D) dual echo in-phase (IP)
and opposed-phase (OP) gradient-echo (GRE) images acquired in the axial
Although dynamic imaging was traditionally performed
utilizing 3-dimensional (3D) T1-weighted fat-saturated spoiled
gradient-echo images, recently developed DIXON-based acquisitions, such
as the mDIXON sequence, allow for more robust fat saturation (ie,
fat-water separation) than traditional sequences that utilize frequency
selective fat saturation techniques.6,7 The combination of
parallel imaging strategies, such as SENSE, with the mDIXON technique
allows for a fast volumetric acquisition of the abdomen with decreased
motion artifacts due to shorter breath-hold times. Furthermore, the
mDIXON technique offers the possibility of reconstructing the acquired
data set as T1-weighted IP, OP, and fat-only images (without penalty of
added acquisition time) in addition to the water-only images (ie, fat
saturated), which are used for the dynamic contrast-enhanced portion of
the study. Pre-contrast mDIXON acquisitions are obtained in oblique
sagittal orientation along the long axis of each kidney and also in the
coronal plane. Coronal ‘fat-saturated’ T1-weighted spoiled gradient-echo
images (mDIXON) are then acquired during a properly timed
corticomedullary phase using a real-time bolus tracking technique
(BolusTrack, Philips Healthcare), and then during the early and late
nephrographic phase at 40 and 90 seconds after the initiation of the
corticomedullary phase. Sagittal oblique mDIXON images are again
acquired along the long axis of each kidney during the excretory phase
after the coronal dynamic acquisition. Finally, an axial mDIXON
acquisition is obtained and ‘water only’ and ‘fat only’ image datasets
are generated. Subtraction of the pre-contrast images from each of the
post-contrast images produce subtracted volumetric image datasets, which
are useful for assessing the presence of enhancement in a renal lesion.
Simple cysts appear as
homogeneously hyperintense thin-walled structures on T2-weighted images,
while septations or solid elements appear hypointense relative to the
hyperintense fluid (Figure1). Numerous thickened septations increase the
likelihood of lesions being malignant.8 Hypointense lesions
on T2-weighted images may represent solid lesions or cystic lesions with
hemorrhagic or proteinaceous contents.9 Signal
characteristics of solid lesions on T2-weighted images may suggest
specific histologic subtyping. Clear-cell RCC, accounting for 65% to 80%
of RCC,10 most commonly demonstrates increased signal intensity relative to the normal renal parenchyma on T2-weighted images.9 Intralesional necrosis, common in clear cell RCC,11 appears as moderate to high signal intensity on T2-weighted images, although it can occasionally appear hypointense.12
Intratumoral hemorrhage and fibrosis can be present and exhibits
variable signal on T2-weighted images. Clear-cell RCC may present with a
capsule or pseudocapsule, which is hypointense on T2-weighted images
and discontinuity of the capsule suggests invasion of the perirenal fat
and higher grade.9,13 Papillary RCC, accounting for approximately 10% to 15% of all RCC,14 demonstrate homogeneous low signal intensity on T2-weighted images,11 although it may also exhibit foci of hemorrhage and necrosis resulting in a more heterogeneous appearance.9 Predominantly
fat-containing lesions, such as some angiomyolipomas (AMLs), appear
hyperintense on T2-weighted images, and exhibit lower signal on
T2-weighted fat-suppressed images. AMLs with minimal fat on the other
hand, exhibit homogeneous hypointense signal relative to renal
parenchyma on T2-weighted images, but should not demonstrate necrotic
In situations where administration of
contrast is contraindicated, T2-weighted images may demonstrate the
presence of tumor thrombus in the renal veins and IVC as a filling
defect of increased signal intensity against background of dark flow
DWI allows for characterization of renal lesions as either solid or cystic based on their degree of restriction of water motion.15
This may be particularly helpful when intravenous contrast cannot be
administered (allergies, renal failure, etc.), precluding evaluation for
enhancement. A lesion that remains hyperintense on high b-value images
and demonstrates low signal on ADC maps is more indicative of a solid
rather than cystic lesion.15 However, restricted diffusion
may be seen in hemorrhagic non-neoplastic contents within a cystic
lesion. Although some authors have shown utility of ADC values in
differentiation of benign lesions and RCC16 or between subtypes of RCC,17 there is considerable overlap in these results, and DWI is not considered as accurate as contrast-enhanced imaging at this time.16
Although DWI may aid in the detection of lymph nodes, malignant from
benign lymph nodes cannot be reliably differentiated based on ADC
T1-weighted dual-phase in-phased (IP) and opposed-phase (OP) gradient
refocused echo (GRE) images, a form of chemical shift imaging, are
particularly useful when evaluating renal lesions. Intracellular lipids
are a relatively common histologic characteristic of clear-cell RCC
(approximately 40% of tumors) and can be detected as foci of decreased
signal intensity on the OP images when compared to the IP images.11,19 Low
signal on OP images relative to IP images can be also seen in the
setting of AMLs that contain only trace amounts of fat, however, those
lesions are indistinguishable from clear cell RCC on these images; the
presence of intravoxel fat (ie, decreased signal intensity on OP imaging
compared to IP imaging) should not be considered diagnostic of AML as
clear cell RCC can also exhibit this finding on MR imaging.20
AMLs with minimal fat, however, tend to be homogeneously hypointense on
T2-weighted images compared to the renal parenchyma, whereas clear cell
carcinomas tend to be heterogeneous hyperintense on T2-weighted images.
The IP and OP phase images may also be helpful to confirm bulk fat in a
lesion, which will appear as high signal on both sets of images,
however, will exhibit a hypointense rim on OP images (India-ink or edge
artifact) at its interface with normal renal parenchyma.9
Homogeneous high-signal intensity within a lesion on unenhanced
T1-weighted images (without India-ink artifact at its interface with the
adjacent renal parenchyma on OP images), as well as on fat-saturated
T1-weighted images (Figure 1) is indicative of hemorrhagic or
Contrast enhancement within a lesion
after the administration of gadolinium is the most reliable way of
differentiating solid from cystic lesions.21 Enhancement
within a cystic lesion can differentiate debris from true solid tissue
(Figure1). Contrast-enhanced T1-weighted images are also used to
characterize the degree and pattern of enhancement, as this is a
reliable differentiating factor between the three most common subtypes
of RCC.22-24 During the corticomedullary phase, clear-cell
RCC demonstrates avid enhancement, papillary RCC demonstrates relatively
low grade enhancement, and chromophobe RCC demonstrates intermediate
enhancement. A percentage SI change threshold of 84% in the
corticomedullary phase has been shown to differentiate clear cell RCC
from papillary RCC with 93% sensitivity and 96% specificity.23
imaging in the coronal or oblique sagittal planes is particularly
helpful to detect small peripheral enhancing components within lesions
that are predominantly cystic. Although most of these lesions containing
“simple” fluid and small solid components represent low-grade
clear-cell RCC, cystic lesions with internal hemorrhage and
peripheral-papillary nodules are more likely to be papillary RCC.19 Other features, such as a delayed enhancing central scar, may favor diagnosis of oncocytoma rather than RCC.9
small size, other challenges in detection of enhancing elements include
pre-contrast high signal within lesions, which may either mimic or mask
enhancing components. Subtraction imaging allows detection of
enhancement above and beyond the native pre-contrast hyperintense signal
within the lesion25 (Figure 1). It also allows for easier detection of low-grade enhancement in lesions, such as in papillary RCC.11
On the other hand, it may reveal lack of enhancement in a lesion that
is hyperintense on post-contrast images owing to inherent high
T1-weighted signal. Another potential confounding factor when evaluating
a renal lesion on T1 pre- and post-contrast images may be inhomogeneous
fat suppression. In addition to decreasing lesion-to-background
contrast, inhomogeneous fat suppression can potentially mask enhancement
when seen adjacent to the lesion in question. The authors have seen
much more reliable and homogeneous exclusion of the fat signal on mDIXON
images compared with 3D, T1, fat-suppressed GRE images.7
Furthermore, mDIXON acquisition allows for reconstruction of IP, OP,
water-only (used for dynamic imaging) and fat-only image datasets. The
fat-only reconstructed images may assist in detection of small amounts
of intracellular lipid within lesions, not readily identified when
comparing the 2-dimensional IP and OP GRE images.
images can help assess the renal vascular anatomy including the arterial
supply to the kidney, which may have surgical implications, as well as
the presence of tumor (ie, enhancing) and/or bland (ie, nonenhancing)
thrombus with the renal vein and IVC.
MR imaging offers advantages over CT and US for characterization of
renal masses and is especially attractive due to its lack of exposure to
ionizing radiation, superior inherent contrast differentiation, and
multiplanar capabilities. A robust high-quality MR protocol, such as the
one outlined in this article, can help facilitate clinical management
or provide viable options for imaging follow-up.
- Mourad WF, Dutcher J, Ennis RD. State-of-the-art management of renal cell carcinoma. American Journal of Clinical Oncology. Epub ahead of print Aug, 2012.
- Zhang J, Pedrosa I, Rofsky NM. MR techniques for renal imaging. Radiologic Clinics of North America. 2003;41:877-907.
- Birnbaum BA, Maki DD, Chakraborty DP,et al. Renal cyst pseudoenhancement: Evaluation with an anthropomorphic body CT phantom. Radiology. 2002;225:83-90.
- Maki DD, Birnbaum BA, Chakraborty DP, et al. Renal cyst pseudoenhancement:Beam-hardening effects on CT numbers. Radiology. 1999;213:468-472.
- Eggers H, Brendel B, Duijndam A, et al. Dual-echo Dixon imaging with flexible choice of echo times. Magnetic resonance in medicine:
Official journal of the Society of Magnetic Resonance in Medicine /
Society of Magnetic Resonance in Medicine. 2011;65:96-107.
TG, Van Tilburg JL, Herigault G, et al. Preliminary clinical experience
with a multiecho 2-point Dixon (mDixon) sequence at 3t as an efficient
alternative for both the SARintensive acquired in- and out-of-phase
chemical shift imaging as well as for 3D fat-suppressed T1-weighted
sequence used for dynamic gadolinium-enhanced imaging. Proceedings, International Society for Magnetic Resonance Medicine. Stockholm, Sweden2010; p. 556.
Sims RD, Yuan Q, Khatri G, et al. Multiecho 2-point Dixon (mDixon)
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- Bosniak MA. The Bosniak renal cyst classification: 25 years later. Radiology. 2012;262:781-785.
- Pedrosa I, Sun MR, Spencer M, et al. MR imaging of renal masses: Correlation with findings at surgery and pathologic analysis. Radiographics: A review publication of the Radiological Society of North America, Inc. 2008;28:985-1003.
- Bostwick DG, Murphy GP. Diagnosis and prognosis of renal cell carcinoma: Highlights from an international consensus workshop. Seminars in Urologic Oncology. 1998;16: 46-52.
- Pedrosa I, Chou MT, Ngo L, et al. MR classification of renal masses with pathologic correlation. European Radiology. 2008;18:365-375.
- Eilenberg SS, Lee JK, Brown J, et al. Renal masses: Evaluation with gradient-echo Gd-DTPA-enhanced dynamic MR imaging. Radiology. 1990;176:333-338.
- Yamashita Y, Watanabe O, Miyazaki T, et al. Cystic renal cell carcinoma. Imaging findings with pathologic correlation. Acta Radiol. 1994;35:19-24.
Leroy X, Zini L, Leteurtre E, et al. Morphologic subtyping of papillary
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- Qayyum A. Diffusion-weighted imaging in the abdomen and pelvis: Concepts and applications. Radiographics: A review publication of the Radiological Society of North America, Inc. 2009;29:1797-1810.
B, Thakur RK, Mannelli L, et al. Renal lesions: Characterization with
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- Wang H, Cheng L, Zhang X, et al. Renal cell carcinoma: Diffusion-weighted MR imaging for subtype differentiation at 3.0 T. Radiology. 2010;257:135-43.
Kwee TC, Takahara T, Luijten PR, et al. ADC measurements of lymph
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- Pedrosa I, Alsop DC, Rofsky NM. Magnetic resonance imaging as a biomarker in renal cell carcinoma. Cancer. 2009;115(10 Suppl):2334-45.
Hindman N, Ngo L, Genega EM, et al. Angiomyolipoma with minimal fat:
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- Rofsky NM, Bosniak MA. MR imaging in the evaluation of small (< or =3.0 cm) renal masses. Magnetic Resonance Imaging Clinics of North America. 1997;5:67-81.
- Kim JK, Kim TK, Ahn HJ, et al. Differentiation of subtypes of renal cell carcinoma on helical CT scans. AJR American J Roentgenol. 2002;178:1499-1506.
Sun MR, Ngo L, Genega EM, et al. Renal cell carcinoma: Dynamic
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Vargas HA, Chaim J, Lefkowitz RA, et al. Renal cortical tumors: Use of
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