Dr. Grossman is a Body MRI fellow, Dr. Khatri is an Assistant Professor, Body/Body MRI section, and Dr. Pedrosa
is the Chief-of-MRI, Associate Professor, Department of Radiology,
University of Texas Southwestern Medical Center, Advanced Imaging
Research Center, Dallas, TX.
A 45-year-old morbidly-obese male (weight 391 lbs (177 kg), BMI
>40) initially presented to an outside institution with an
obstructing rectosigmoid mass in March 2009. The patient underwent an
abdominoperineal resection in April 2009 (T4 lesion with 1/34 nodes
positive) and was then treated with chemoradiation followed by
chemotherapy until December 2009. After several follow-up computed
tomography (CT) scans without evidence of metastatic disease, an outside
surveillance CT in April 2012 identified 2 new liver lesions; only one
was confirmed on an FDG positron emission tomography (PET) scan in May
2012. Carcinoembryonic antigen remained within normal limits before and
after surgery. The patient transferred care to our institution for
consideration of surgical resection of hepatic metastasis in May 2012.
The patient underwent a multiphasic CT with intravenous contrast,
which was limited by streak and beam hardening artifact from the patient
touching the CT gantry, and identified a single heterogeneous
indeterminate lesion in the right lateral hepatic lobe (Figure 1). This
was the lesion that was seen on the prior PET/CT (Figure 1). Given the
patient’s body habitus, an magnetic resonance imaging (MRI) examination
of the liver was obtained on a large-bore magnet (Philips Ingenia 1.5T,
70-cm bore), which allows for imaging of patients up to 550 lbs (250
kg). The patient was imaged with a torso 16-element digital phased-array
surface coil. A hepatobiliary contrast agent, Gadoxetate disodium
(Eovist; Bayer HealthCare Pharmaceuticals), was utilized to increase
conspicuity between the normal liver parenchyma and potential
metastases.1 Six hypoenhancing lesions consistent with
metastatic disease were identified with MRI. While some of the lesions
were identified on the T2-weighted, diffusion weighted and/or dynamic
post-contrast images obtained during the arterial and portal phases,
they were better depicted during the hepatobiliary phase acquired 20
minutes after administration of contrast (Figure 1).
Multiple colorectal metastases to the liver
The liver is the most common site of metastatic spread in patients
with colorectal adenocarcinoma. Almost 50% of patients with colorectal
cancer develop metachronous metastasis in the liver at some time after
their primary resection.2 New advances in chemoradiation have
resulted in improved mortality in patients with metastatic colorectal
cancer although surgical resection is still considered the only
therapeutic option with potential long-term survival. While the
indications for surgical resection of hepatic metastases continue to
evolve, the number and location of metastatic lesions remain a critical
aspect of the assessment of patients being considered for this
therapeutic option. Therefore, optimal imaging of the liver is crucial
for pre-surgical evaluation of a patient with colorectal cancer.
Metastatic colorectal adenocarcinoma to the liver commonly presents
as hypoenhancing lesions, better seen during the portal venous phase
when the uninvolved liver parenchyma enhances avidly. As such, it is
frequently challenging to diagnose the presence of small liver lesions,
as their detection may be challenged by normal vascular structures
and/or the presence of benign incidental lesions (eg, hepatic cysts,
hemangiomas). Furthermore, the detection of small hepatic metastasis may
be obscured by respiratory artifacts. Additionally, the phenomenon of
pseudoenhancement on CT further contributes to the difficulty in
detecting small hypovascular liver metastases.3
The liver-specific contrast agent Gadoxetate disodium is transported
from the extracellular space into functioning hepatocytes, where the
molecule is subsequently excreted through the hepatobiliary pathway. In
patients with normal hepatorenal function, approximately 50% of the
agent is excreted via the hepatobiliary pathway.4 Imaging in
the late arterial, portal venous and early delayed phases is similar to
conventional gadolinium agents, as the molecule is within the
extracellular blood volume during these acquisitions. The unique
20-minute delayed phase reflects hepatobiliary excretion, as only
functioning hepatocytes and bile ducts are hyperintense. Lesions within
the liver composed of other cells will be hypointense relative to the
background liver, which increases the conspicuity of small
nonhepatocellular lesions, such as metastases. The increased sensitivity
of Eovist MRI for liver metastases has been reported in the literature.1,5
This case illustrates the technical challenges to adequately imaging a
larger patient. The CT images obtained were noisy and demonstrated some
beam hardening artifact generated due to the patient’s abdominal wall
contacting the CT gantry. This examination vaguely demonstrated only the
largest lesion, which measured 3 cm in craniocaudal dimension. The
patient also exceeded the weight and size limit on several MR magnets at
the authors’ institution. The ability to perform the MRI examination in
a large-bore MRI scanner (70-cm wide), with up to 55-cm field-of-view,
provided the opportunity to fit this larger patient comfortably and
obtain images of the liver with high diagnostic quality.
Furthermore, digital surface coils, which directly digitize the MR
signal before the images are sent to the magnet, provide an improved
signal-to-noise ratio over standard analog surface coils, which may be
essential in challenging patients, such as the one presented here. In
this large patient, the combination of existing hardware, together with
the homogeneous fat exclusion achieved with the optimized mDIXON
acquisition,6,7 and the administration of a hepatobiliary
agent (Eovist) were critical to altering the therapeutic approach by
demonstrating several unsuspected liver metastases.
The synergism of state-of-the-art MRI hardware, including a large
70-cm bore, improved signal-to-noise from digital coils, optimized fat
exclusion over large fields-of-view using a Dixon-based acquisition
(mDIXON), and the use of an hepatobiliary agent (Eovist) were essential
in detecting very small lesions in a morbidly obese patient that were
not identified on contrast-enhanced CT and PET imaging. This MRI
examination was crucial in making a decision about the best treatment
options for this patient.
- Bluemke DA, Sahami D, Amendola
M, et al. Efficacy and safety of MR imaging with liver-specific
contrast agent: U.S. multicenter phase III study. Radiology. 2005;237:89-98.
D, Gallinger S, Nhan C, et al. The role of liver resection for
colorectal cancer metastases in an era of multimodality treatment: A
systematic review. Surgery. 2012;151:860-870.
R, Kissane J, Sarwani N, et al. Pseudoenhancement of renal cysts:
Influence of lesion size, lesion location, slice thickness, and number
of MDCT detectors. AJR Am J Roentgenol. 2012;198:133-7.
KI, Husarik DB, Sirlin CB, et al. Gadoxetate disodium–enhanced MRI of
the liver: Part 1, protocol optimization and lesion appearance in the
noncirrhotic liver. AJR Am J Roentgenol. 2010;195:13-28.
Huppertz A, Balzer T, Blakeborough A, et al. Improved detection of
focal liver lesions at MR imaging: Multicenter comparison of gadoxetic
acid-enhanced MR images with intraoperative findings. Radiology. 2004;230:266-275.
Perkins 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 SAR-intensive 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. Proc. Intl Soc Mag Reson Med. Stockholm, Sweden 2010;18:556.
Sims RD, Yuan Q, Khatri G, et al. Multiecho 2-Point Dixon (mDIXON)
imaging as an alternative to separate 2D chemical shift imaging and 3D
fat-suppressed T1-weighted sequences for gadolinium enhanced imaging.
Poster Presentation. Intl Soc Mag Reson Med. Melbourne, Australia. 2012.