September 10, 2014 -- Thanks to its
high negative predictive value, ultrasound elastography with intrinsic
compression may be able to reduce by one-third the number of unnecessary
biopsies performed on calcified thyroid nodules, according to research
published in the October issue of Ultrasound in Medicine and Biology.
In a study involving 65 calcified
thyroid nodules, a team of researchers led by Dr. Min-Hee Kim of Catholic
University in Korea found that elastography yielded 95.8% negative predictive
value in detecting malignancy. Furthermore, more than one-third of biopsies on
calcified nodules could have been avoided based on elastography results.
"Intrinsic compression
elastography can be used in conjunction with B-mode [ultrasound] to reduce the
number of [fine-needle aspiration] biopsies of calcified thyroid nodules,"
wrote Kim and colleagues, who also came from the University of Washington and
Pohang University of Science and Technology.
Confounding calcification
Although calcification in thyroid
nodules is an important ultrasound feature that suggests malignancy, and
current major guidelines strongly recommend that calcified nodules larger than
5 mm be biopsied, calcification can be present in both malignant and benign
nodules. As a result, many benign nodules end up being biopsied unnecessarily (Ultrasound
Med Biol, October 2014, Vol. 40:10, pp. 2329-2335).
Ultrasound elastography has been
shown in a number of studies to provide high sensitivity and specificity for
detecting malignant thyroid nodules. But the lack of interobserver agreement in
elastography -- due to variability in data acquisition and scoring -- is a
major reason why the method has not been widely adopted in clinical practice,
according to the group.
Standard elastography utilizes
external compression, with the pressure of the transducer providing the tissue
compression that results in the tissue strain measured by elastography. But
other researchers have found that elastography utilizing intrinsic compression
-- with pressure provided by forces inside the body such as carotid artery
pulsation -- could offer better performance. The payoff would be better
interobserver and intraobserver agreement.
As a result, the team sought to
determine if intrinsic compression elastography could perform well for
characterizing thyroid nodules with calcification. The researchers recruited
188 patients with 229 thyroid nodules who were referred to Seoul St. Mary's Hospital
from May 2011 through January 2012 for a fine-needle aspiration (FNA) biopsy.
All patients received both
ultrasound and elastography exams prior to FNA biopsy. B-mode images were
acquired using an iU22 ultrasound system (Philips Healthcare) with a 5- to 12-MHz
high-resolution linear probe.
Blinded to the patient's clinical
information as well as cytologic and elastography results, a radiologist with
15 years of experience retrospectively reviewed the B-mode ultrasound images
and extracted nodule features such as echogenicity, margin, shape, and presence
of calcification, according to the researchers. Based on those ultrasound
features, the nodules were categorized into three groups: benign,
indeterminate, and suspicious for malignancy.
The elastography studies were
performed by three endocrinologists with more than one year of experience with
intrinsic compression elastography. An Accuvix XG (Samsung Medison) scanner with an L5-13 linear
transducer was used in the study, and no external compression was performed
while the ultrasound data were acquired, according to the team.
The researchers employed a
quantitative scoring method -- elastic contrast index (ECI) -- for the
elastography results; a higher ECI value suggests a stiffer nodule and an
increasing likelihood of malignancy. A minimum of two ECI measurements were
gathered in the imaging plane that showed the thyroid nodule's largest diameter
in the transverse view, according to the authors.
Diagnostic accuracy
Next, the researchers determined
elastography's diagnostic accuracy by varying the ECI cut-off value in order to
find the sensitivity and specificity combination that yielded the maximum
geometric mean (sensitivity multiplied by specificity) in detecting malignant
nodules. They also calculated positive and negative predictive values.
Of the 196 nodules in the study, 42
were malignant; all were papillary thyroid carcinoma. The mean nodule size was
9 ± 4.17 mm for malignant nodules, significantly smaller than the 11.31 ± 6.1
mm mean size for benign nodules.
The researchers observed that the
mean ECI value of malignant nodules (4.51 ± 2.22) was significantly higher than
the value for benign nodules (2.98 ± 1.47, p < 0.001). They then calculated
elastography's performance, with a mean ECI cut-off value of 3.11 indicating
malignancy.
The radiologist classified four of
the 65 (45 benign and 20 malignant) nodules with calcification as benign; three
of the four were found to be benign under elastography. The remaining 61
nodules with calcification were categorized as either indeterminate (29) or
suspicious for malignancy (32). With elastography, however, nine of the 32
nodules classified as suspicious for malignancy were determined to be benign, a
diagnosis that was confirmed by biopsy.
Furthermore, 12 of the 29 cases that
were considered by the radiologist to be indeterminate were judged to be benign
on elastography. Biopsy results confirmed the benign diagnosis in 11 of 12
cases; one malignant nodule with rim classification was incorrectly classified
as benign using elastography, according to the group.
Elastography's performance in
nodules with calcification was as follows:
- Sensitivity: 95%
- Specificity: 51.1%
- Positive predictive value: 46.3%
- Negative predictive value: 95.8%
In all, 23 benign calcified nodules
(51.1% of benign calcified nodules) were correctly classified by elastography,
whereas only four (8.9%) were correctly classified by B-mode ultrasound, the
authors wrote.
The study demonstrates a potential
role for elastography in the management of calcified thyroid nodules, according
to the researchers.
"With the use of elastography
on those calcified nodules, for which B-mode [ultrasound] has low specificity
(i.e., 8.9%) in detecting malignancy, FNA biopsy could have been avoided in 23
(35.4%) of 65 calcified nodules," they wrote. "In terms of reducing
the number of FNA biopsies, our study found that elastography had a clinical
impact similar to that reported in a previous study that evaluated the
usefulness of elastography in calcified breast lesions."
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