Role of ultrasonography (US) and standard dynamic magnetic
resonance imaging in detection and characterization of computed
tomography (CT) diagnosed indeterminate lesions at patient with
underlying cancer
Arvin Aryan & Hamidreza sadeghian
Assistant Professor of radiology. Tehran University of medical science. Imam Khomeini hospital Complex. Cancer institute department
Resident of radiology. Tehran University of medical science. Imam Khomeini hospital Complex.
Abstract
Introduction: The purpose of our study was to
determine efficacy of ultrasonography (US) and
diffusion weighted magnetic resonance
imaging (DWI) for the characterization of small (<15
mm) hepatic lesions described as indeterminate
lesions on prior computed tomography (CT) scans in
patient with cancer.
Methods: Small hepatic masses in 30 patients
considered indeterminate on prior CT scans were
included in the study for identified indeterminate small
hepatic lesions (< 15 mm). Then, US and MRI
examinations were performed for all of patients. Two
radiologists used agreement reading of established US
and MRI to characterize indeterminate small lesions as
simple cysts, hemorrhagic cysts, lipoma, adenoma ,
hemangioma or metastasis.
Results: 30 indeterminate small hepatic lesions were
and 10 and 21 benign lesions among those with
pathologic follow-up by US and MRI respectively.12
lesions could not be characterized with US.
Conclusion: US and MRI can be an effective
method for characterizing lesions small (<15 mm)
hepatic masses found to be indeterminate by CT. In
addition MRI is better than US offers only marginal
benefit for detection and characterization of
indeterminate small lesions in liver.
Introduction
Small hypo-dense lesions in the liver are
common and usually are smaller than 1.5 cm
in adult with cancers [1-3]. These lesions in
liver are vulnerable to volume averaging and
pseudo-enhancement and then are
challenging to characterize perfectly by
examinations in patients with cancers, the
characterization of these lesions due to
nonspecific imaging features and small size
of lesions is difficult and as some patients
have multiple small lesions, taking biopsy
from all lesions is not fusible.
Characterization of small hypo-dense lesions
is important, because these lesions are
generally presumed to be benign; therefore
further characterization is generally not done
[6, 7]. Further characterization by MRI for
such lesions in patients is desirable [8, 9],
because the presence of hepatic metastasis
may substantially alter prognosis and therapy
[10].
MRI is a useful modality that enables
radiologists to detect and characterize lesions
in all organs due to its superior contrast
resolution [11, 12]. MRI has reported use in
characterizing small lesions in the liver that
are not fully distinguished by CT
examination, and they have the potential to
definitively characterize indeterminate small
hypo-dense lesions in the liver[8, 9, 13]. MRI
has been reported to successfully allow
radiologists to distinguish with moderate to
good inter observer agreement benign and
malignant hepatic lesions in patients with
indeterminate findings on CT[11].
MRI is frequently ordered by clinicians for
further characterization of hepatic lesions
considered too small to characterize by our
radiologists. To our knowledge, no study to
date has evaluated the role of MRI in
characterizing small hypo-dense lesions in
the liver seen on CT examination in patients
with cancer. We undertook this study to
assess the value of hepatic MRI for
differentiating benign and malignant causes
of hepatic lesions too small to characterize
detected on CT in patients with cancer.
Materials and Methods
This prospective study was approved by our
institutional (at the University of Tehran)
review board. Patient consent was waived.
From July 2015 to July 2017, we
prospectively queried our electronic
radiology database to identify dedicated liver
MRI in the radiology report and US
examinations were done by one radiologist
for each patient. The perspective identified a
total of 33 patients with cancer. For all
patients, our database was searched for
dedicated CT examinations that had been
performed before the MRI and US
examinations. All patients were referred to
undergo MRI and US study for the
characterization of liver lesions measuring
less than 15 mm because the CT report
declared the liver lesions as indeterminate or
too small to characterize. Three of the 33
patients who were identified were excluded
from the study, including patients who took
chemotherapy before imaging. These 30
patients were the lesions evaluated in this
study. Thus, in this study comprised a total of
30 consecutive patients with dedicated liver
CT and MRI/US examinations. All 30
patients MRI and US examinations were
performed to evaluate an indeterminate liver
lesion smaller than 15 mm that was seen on
CT examinations. Lesions were characterized
as indeterminate if they were smaller than 15
mm, did not meet simple fluid or fat density
criteria on unenhanced CT, had
indeterminate enhancement or were too small
to identify on unenhanced images and
therefore could not be assessed for
enhancement.
Data Collection
The official radiology reports and the
associated CT scans and subsequent MRI
images and US were reviewed to classify the
reported MRI results for each hepatic lesion
as benign, malignant, or of indeterminate
of indeterminate cause on the first MRI
evaluation, the results of subsequent imaging
evaluations. The data were analyzed on a
per-patient basis and based on the number of
lesion diagnoses reported on MRI for each
patient. The official radiology reports and
clinical records were reviewed for
assessment of the presence of extra hepatic
metastasis.
Imaging Technique
Most of the CT examinations were performed
at our institution on MDCT scanners at 7.0-
or 7.5-mm collimation. Scans were obtained
during the portal venous phase after power
injection of IV contrast material. Patients
were instructed to fast for 4 hours before MRI
examination. All MRI examinations were
performed at our institution on 3-T
magnetom scanners according to various
protocols that included at least 1-Coronal T2-
haste weighted single-shot fast spin echo
(FSE) without fat suppression, 2- Axial
T1-weighted dual-echo spoiled gradient-echo
sequence, 3-Axial T2-weighted FSE out with
fat suppression and respiratory triggering,
axial T2Fs and axial T2 heavily, 4-Coronal
T1-weighted pre- and post-dynamic
gadolinium-enhanced imaging using
three-dimensional, and 5- Post-contrast delayed
excretory phase axial T1-weighted
2-dimensional spoiled gradient echo with fat
suppression. Axial images were acquired at
3-5mm slice thickness and coronal images at
5-mm thickness.
Lesion Characterization
Each case was reviewed prospectively and
independently by two board-certified
radiologists who specialized in abdominal
imaging and who had 5 years of
post-fellowship experience reviewed the CT and
MRI examinations. They used consensus
reading to determine image quality and to
identify renal lesions that met the study
prior knowledge of the original interpretation
of the studies or the final diagnosis. Each
lesion was divided to benign, indeterminate,
and malignant.
T1 and T2 signal and enhancement
characteristics of the lesions were taken into
account during MRI characterization of the
lesion. Subtraction techniques were used to
evaluate lesion enhancement. Enhancement
was defined as a subjective internal signal
intensity in the lesion that was greater than
the background enhancement on subtraction
images. A lesion that showed enhancement,
regardless of T1 and T2 signal
characteristics, was categorized as a solid
hepatic mass. A lesion with markedly high
signal on T2-weighted images, low signal on
T1-weighted images, and no enhancement
was characterized as a simple cyst. A lesion
with high signal on fat-suppressed
T1-weighted images but with no demonstrable
enhancement was labeled as a proteinaceous
or hemorrhagic cyst. A lesion for which MRI
showed features of gross fat, including high
signal on T2-weighted images, loss of signal
on fat-suppressed images, or in phase/out
phase image on opposed-phase imaging
using the India-ink artifact, was classified as
steatotic type of adenoma or
angiomyolipoma no wash in wash out.
Results
Lesion Characterization by MRI
The specific diagnoses of hepatic lesions too
small to characterize reported on MRI and
US included benign lesion (n = 21 and n = 10
respectively) and metastasis (n = 9 and n = 8
respectively).12 lesions could not be
characterized with US. In zero (0%) of the
subjects, the hepatic lesions too small to
characterize on CT remained of
indeterminate cause on MRI. Of the 30 small
lesions that were incompletely characterized
by CT, 30 were confidently characterized by
hemangiomas or adenomas , and 9 were
metastasis(one case esophageal cancer, three
cases colon cancer ,one case ovarian cancer
,one case endometrial cancer, one case
neuroendocrine tumor ,one case RCC of
kidney and one case cancer of gall
bladder).hepatic lesions showed different
patterns of enhancement as below.
Hemangiom: marked high T2 + no signal
drop on heavily T2+no restriction on DWI+
PNE
Adenoma : Mild to moderate high T2 + signal
drop on in phase/out phase
FNH : marked high T2 +hyper signal T2 scar
/ arterial enhancement+ central scar high on
T2
HCC : mild –moderate T2 + wash in wash out
+ capsule..
Discussion
Liver lesions smaller than 15 mm are
frequently detected by CT examination in the
abdomen [2]. Small lesions in liver have
several benign and malignant causes, and
many are not readily characterizable on
imaging studies, particularly when smaller
than 1 cm [1]. In this study 70% and 33% of
small lesions in liver were considered benign
after use of MRI or US respectively. This
percentage is smaller than that reported by
Schwartz,et al[2], likely due to of the
different criteria used to define small hepatic
lesions. Benign liver tumors have been
reported in up to 52% of the general
population [14].
Some of small lesions in liver such as cysts,
hemangiomas, focal nodular hyperplasia, and
adenomas are asymptomatic and are revealed
incidentally at imaging examinations [1]. It is
often challenging to characterize such small
liver lesions with imaging studies, and biopsy
can be difficult [2]. In a patient without
known cancer, these lesions usually can be
evaluated with serial follow-up imaging tests
patients with known malignancy however,
understanding of tumor development is
critical for determining prognosis and
treatment [2].
Liver lesions are frequently detected in daily
clinical practice and if the lesion cannot be
fully characterized, follow-up imagings
including MRI or CT are usually
recommended [15]. Although both CT and
MRI are considered suitable for the
evaluation of indeterminate lesion, CT had
some limitation for reorganization small liver
lesions (<15 mm) [15]. Partial volume
averaging and pseudoenhancement are the
main causes of the lacks of ability of CT to
determine the nature of a small liver lesion
[5].Slice thickness in CT is more than half
the diameter of the lesion and often cusses
volume averaging becomes more pronounced
which named partial volume averaging [16].
Partial voluming averaging can make CT
difficult for assessment of the attenuation
value and enhancement [15]. Partial volume
averaging could be decrease by using thin CT
slices to assess the density of a lesion, but thin
slices have much higher image noise can
potentially result in an incorrectly higher CT
number [16, 17]. Pervious report have shown
that CT examination can lead to
mischaracterization of a cyst as an enhancing
mass, which named pseudoenhancement, due
to incorrectly reveal enhancement of up to 50
HU[18].The degree of pseudoenhancement is
inversely associated to size of lesions [19].
The pseudoenhancement unnaturally
increased attenuation values in small lesions,
which are centrally located in the
parenchyma, in the presence of intravenous
contrast [15].
In comparison with CT, MRI had superior
soft-tissue contrast and is not limited by
pseudoenhancement. Furthermore, use of
subtraction images in MRI allows more
absence of enhancement in liver lesions.
Cystic lesions had marked hyper-intensity on
T2-weighted images, and lesions with
intra-lesion hemorrhage or high proteinaceous
contents are hyper-intense on
T1-weightedimages [17].
Conclusion
Results from this study showed that small
liver lesions in patients with cancer more
often are benign than malignant, these
lesions represent metastases in 30% of
patients. In addition, MRI has the potential
to characterize small lesions better than US,
and CT due to high tissue contrast and then
suggest that MRI can be the preferred
modality over US, and CT.
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