Incidental Thyroid Lesions Detected on 18F ... - KoreaMed Synapse

Original Article pISSN 1738-2637 / eISSN 2288-2928 J Korean Soc Radiol 2014;71(3):111-119 http://dx.doi.org/10.3348/jksr.2014.71.3.111

Incidental Thyroid Lesions Detected on 18F-Fluorodeoxyglucose Positron Emission Tomography/CT in Patients with Non-Thyroidal Cancer: Clinical Implications and the Value of Ultrasound1 비갑상선암 환자에서 시행한 18F-Fluorodeoxyglucose Positron Emission Tomography/CT에서 발견된 갑상선 우연종에 대한 초음파의 임상적 가치에 대한 연구1 Kwang Hwi Lee, MD1,2, Jung Hee Shin, MD1, Boo-Kyung Han, MD1, Eun Young Ko, MD1, Eun Sook Ko, MD1, Soo Yeon Hahn, MD1, Joon Young Choi, MD3 Departments of 1Radiology, 3Nuclear Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea 2 Department of Radiology, Haeundae Paik Hospital, Inje University College of Medicine, Busan, Korea

Purpose: To evaluate the clinical implications of subsequent ultrasound (US) for incidental thyroid lesions (ITLs) detected on positron emission tomography/computed tomography (PET/CT) in patients with non-thyroidal cancer. Materials and Methods: We retrospectively searched for ITLs in 2703 patients with non-thyroidal cancer on 3226 PET/CT examinations. We divided the patients into two groups: US-performed and US-not performed groups. Diagnostic performance of US in detecting malignancy was analyzed according to the PET/CT findings. Results: The incidence of ITLs on PET/CT in patients with non-thyroidal cancer was 8.4% (226/2703). Death rate from disease and stage were not significantly different between the groups. The malignant rate of ITLs that had cytopathology was 39% (22/57). All malignancies were primary thyroid cancers except for one metastasis. Overall diagnostic performance of US was 87% sensitivity, 66% specificity, 66% positive predictive value (PPV), and 89% negative predictive value (NPV). The diagnostic performance of US according to the PET/CT findings was probable benign on PET/CT (n = 9): 100% specificity, 100% NPV; suspicious malignant on PET/CT (n = 22): 75% sensitivity, 90% specificity, 90% PPV, 75% NPV; and undetermined on PET/CT (n = 26): 100% sensitivity, 94% specificity, 91% PPV, 100% NPV. Conclusion: ITLs did not affect the prognosis of patients with non-thyroidal cancer whether subsequent US was performed or not. Subsequent US may be unnecessary for ITLs with probable benign findings on PET/CT.

Index terms Thyroid Disease Positron Emission Tomography Ultrasound Malignancy

Received May 14, 2014; Accepted June 18, 2014 Corresponding author: Jung Hee Shin, MD Department of Radiology, Samsung Medical Center, Sungkyunkwan University School of Medicine, 81 Irwon-ro, Gangnam-gu, Seoul 135-710, Korea. Tel. 82-2-3410-6420 Fax. 82-2-3410-0049 E-mail: [email protected] This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

and follow-up for primary and metastatic lesions in patients

INTRODUCTION

with various kinds of malignancies (2). The current widespread

Incidental thyroid lesions (ITLs) detected on 18F-fluorodeoxy-

use of 18F-FDG PET/CT in patients with non-thyroidal malig-

glucose (18F-FDG) positron emission tomography/computed

nancies has resulted in an increase in detection of ITLs. The

tomography (PET/CT) are defined as incidentally found abnor-

strategy for managing these lesions is important for predicting

malities in the thyroid gland on F-FDG PET/CT in patients

patient prognosis and cost-effectiveness.

18

with non-thyroidal disease (1). F-FDG PET/CT is increasingly

Ultrasound (US) and subsequent US-guided fine needle aspi-

used to evaluate localization, stage of primary index tumors,

ration (US-FNA) are widely recommended for evaluating ITLs

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Copyrights © 2014 The Korean Society of Radiology

111

Subsequent US Revealed Limited Diagnostic Value for Incidental Thyroid Lesions Detected on PET/CT

to enhance diagnostic accuracy (3). However, the question aris-

performance of US to detect malignancy as follows: sensitivity,

es if such a strategy is sensible in patients with underlying ma-

specificity, positive predictive value (PPV) and negative predic-

lignancies and various PET/CT findings. When abnormal le-

tive value (NPV), according to the 18F-FDG PET/CT findings.

sions of the thyroid gland are present on 18F-FDG PET/CT, patients with non-thyroidal malignancies are justified for fur-

F-FDG PET/CT

18

ther evaluation, as compared to the healthy screening popula-

All patients fasted for at least 6 hours prior to the 18F-FDG PET/

tion. Therefore, subsequent US or US-FNA could possibly be

CT examinations but were allowed to drink water. The 18F-FDG

overused. Sensitivity and specificity of F-FDG PET/CT to dif-

PET/CT scans were performed using a GE Discovery LS PET/CT

ferentiate malignancies from benign thyroid lesions have been

scanner (GE Healthcare, Milwaukee, WI, USA). A whole-body

reported to be 60−80% and 66−91%, respectively (2). Although

CT scan was performed using a continuous spiral technique with

the diagnostic value of F-FDG PET/CT and US for abnormal

an eight-slice helical CT that had a gantry rotation speed of 0.8

thyroid lesions has been reported in many studies (3-5), no re-

second. The acquisition protocol of the CT scan was as follows:

port has evaluated the diagnostic value of subsequent US ac-

40−120 mAs adjusted by body weight, 140 kVp, a section slice

cording to 18F-FDG PET/CT findings for ITLs, particularly in

width of 5 mm, and a table feed of 5 mm per rotation. Neither in-

patients with non-thyroidal malignancies, which are frequently

travenous nor oral contrast agent was used. After the CT scan was

encountered in clinical practice.

obtained, PET imaging was obtained at 60 ± 5 minutes after intra-

18

18

The purpose of this study was to evaluate the clinical implica-

venous injection of 370 MBq 18F-FDG. We reconstructed PET

tions and value of subsequent US for ITLs detected on 18F-FDG

images using CT data for attenuation correction and image fusion

PET/CT in patients with non-thyroidal cancer according to F-

and an ordered subset expectation maximization algorithm (28

FDG PET/CT findings.

subsets, two iterations) with Gaussian smoothing filter (full width

18

at half maximum = 5.45 mm). The trans-axial images were

MATERIALS AND METHODS

scanned in a 128 × 128 matrix (pixel size = 4.29 × 4.29 mm) with

Patients

Healthcare, Milwaukee, WI, USA) was applied to exactly co-reg-

a slice thickness of 4.25 mm. Commercial software (Xeleris, GE

This retrospective study was approved by our Institutional Re-

ister the separate CT and PET scan data.

view Board, and the informed consent requirement was waived.

We divided 18F-FDG uptake into two patterns of focal: 18F-

A total of 3226 18F-FDG PET/CT examinations in 2703 patients

FDG uptake in less than a lobe of the thyroid gland or diffuse:

with non-thyroidal cancer were performed between March

18

2006 and March 2008 at the nuclear medicine department of

sidered 18F-FDG uptake as abnormal on the visual analysis, we

our institution. The patients underwent 18F-FDG PET/CT for

drew three-dimensional regions of interest to quantify the maxi-

cancer staging before treatment, detection of distant metastasis,

mum standardized uptake value (SUVmax) normalized for

and localization of a recurrent tumor.

body weight. ITLs were defined as an increase in 18F-FDG up-

F-FDG uptake in near or an entire thyroid gland. When we con-

Patients with ITLs detected on 18F-FDG PET/CT were divid-

take on PET and/or an abnormal attenuated lesion on CT in any

ed into a US-performed group in which subsequent US was

portion of the thyroid gland, regardless of a focal or diffuse pat-

performed to evaluate thyroid lesions after F-FDG PET/CT,

tern. A thyroid incidentaloma was defined as a focal lesion that

and a US-not performed group in which subsequent US was

revealed focal 18F-FDG uptake on PET or a nodule on CT. The

not performed. Subsequent US was determined at the clinician’s

18

discretion. The two groups were compared with regard to age,

three categories of suspicious for malignant: unilateral/focal 18F-

death rate from disease, and non-thyroidal cancer stage.

FDG uptake with SUVmax > 4.2; probably benign: bilateral/dif-

18

F-FDG PET/CT findings were retrospectively classified into

US findings were analyzed for patients in the US-performed

fuse 18F-FDG uptake with SUVmax < 1.3 or no discernible thy-

group who underwent surgery or sufficient clinical and radio-

roid nodule on CT; and undetermined: categorized into neither

logic follow-up of at least 1 year. We analyzed the diagnostic

suspicious for malignant nor probably benign (6).

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J Korean Soc Radiol 2014;71(3):111-119

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Kwang Hwi Lee, et al

primary non-thyroid malignancy were analyzed by Pearson’s

US and US-FNA US examinations were performed using high-resolution US

chi-square test or the Wilcoxon rank-sum test, and 3 year mor-

equipment (IU22; Philips Medical Systems, Bothell, WA, USA

tality rates were analyzed by Pearson’s chi-square test. The diag-

or HDI 5000; Advanced Technology Laboratories, Bothell, WA,

nostic performance of US was analyzed by McNemar’s chi-

USA) with 5−12 MHz linear array transducers by one of seven

square test. p values < 0.05 were considered significant. Numeric

board-certified radiologists. US examinations included an eval-

data are expressed as mean ± standard deviation.

uation of the whole thyroid gland and the lateral neck compartments (levels I, II, III, IV, or V). The US diagnosis was divided into “suspicious for malignant” and “probably benign”. Suspi-

RESULTS

cious for malignant US findings included taller-than-wide

The incidence of ITLs detected on 18F-FDG PET/CT exami-

shape, infiltrative margin, microcalcifications, and marked hy-

nations was 8.4% (226 of 2703 patients with non-thyroidal can-

poechogenicity (7). We diagnosed nodules as “suspicious for

cer) (Fig. 1). Among the 226 patients, 82 (36%) showed diffuse

malignant” if there was one or more suspicious findings.

18

F-FDG uptake, and 144 (64%) had focal lesions with or with-

US-FNA was performed by radiologists. Using the freehand technique and direct US visualization, a 23-gauge needle tip was

out 18F-FDG uptake. The incidence of thyroid incidentaloma (focal lesion) on 18F-FDG PET/CT was 5.3% (144/2703).

placed in the targeted lesion below the center of the transducer and

Of the 226 patients with ITLs, the US-performed group was

was advanced to the lesion along the image plane. The aspirated

composed of 78 (35%) and the US-not performed group was

material was placed on appropriately labeled glass slides, smeared,

comprised of 148 (65%). The US-performed group included 27

and fixed in 95% ethanol. The remainder of the material within the

males and 51 females (mean age, 59.9 ± 11.8 years; range, 33−82

syringe was rinsed with ethanol for processing as a cell block. The

years). The US-not performed group was 40 males and 108 fe-

slides were sent to the pathology department for analysis.

males (mean age, 56.6 ± 11.6 years; range, 14−82 years). The age of patients in the US-performed group was significantly older than that in the US-not performed group (p = 0.037), but sex

Statistical Analysis The statistical analysis was performed using SPSS software

and stage of non-thyroidal malignancies were not significantly

(SPSS Inc., Chicago, IL, USA). Patient age, sex, and staging of

different between the two groups (Table 1). The 3-year mortality

3226 18F-FDG PET/CT scans is nonthyroidal cancer patients (n = 2703) Incidental thyroid lesions on 254 18F-FDG PET/CT scans (n = 226, 8.4%) (82: diffuse lesions, 144: focal lesions) US-performed group (n = 78) (9: diffuse lesions, 69: focal lesions)

Cytopathologic confirmation (n = 57) Surgery (n = 13) US-FNAB with at least 1-year US F/U (n = 44)

Malignant (n = 22) PTC (n = 20) MTC (n = 1) Metastasis (n = 1) (1: diffuse lesions, 21: focal lesions)

Benign (n = 35) NH (n = 22) LT (n = 4) Cyst (n = 2) Others (n = 7) (4: diffuse lesions, 31: focal lesions)

US-not performed group (n = 148) (73: diffuse lesions, 75: focal lesions)

US and clinical F/U at least a year (n = 21)

No clinical evidence of malignancy (n = 21)

Fig. 1. Flow chart of the participants in the study. Note.-F/U = follow-up, LT = lymphocytic thyroiditis, MTC = medullary thyroid carcinoma, NH = nodular hyperplasia, PET/CT = positron emission tomography/computed tomography, PTC = papillary thyroid carcinoma, US-FNAB = ultrasound-guided fine needle aspiration, 18F-FDG = 18 F-fluorodeoxyglucose

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Table 1. Comparison of Clinical Characteristics of the Patients with Abnormal Thyroid Lesions on PET/CT between US-Performed Group and US-Not Performed Group Gender (M/F) Age Stage* 1 2 3 4 Not available Death rate from non-thyroidal cancer

US-Performed Group (n = 78) 27/51 59.9 ± 11.8 (range, 33−82)

US-Not Performed Group (n = 148) 40/108 56.6 ± 11.6 (range, 14−82)

21 (27%) 8 (10%) 15 (20%) 8 (10%) 26 (33%) 20 (26%)

37 (25%) 15 (10%) 27 (18%) 21 (14%) 48 (33%) 47 (32%)

p Value 0.301 0.037 0.948

0.421

Note.-*Stage of non-thyroidal cancer. PET/CT = positron emission tomography/computed tomography, US = ultrasound Table 2. Primary Non-Thyroidal Cancers with Incidental Thyroid Lesions in US-Performed Group and US-Not Performed Group US-Performed Group US-Not Performed (n = 78) Group (n = 148) Lung cancer Colon cancer Stomach cancer Breast cancer Cervical cancer Endometrial cancer Lymphoma Liver tumor Pancreas cancer Bile duct tumor Renal tumor Ovarian cancer Esophageal cancer Head and neck cancer Other

34 9 9 6 4 2 2 2 2 1 1 1 1 1 3

37 12 16 19 11 2 14 1 7 5 0 5 3 8 8

thology was 39% (22/57). All malignancies were primary thyroid cancers except for one metastasis arising from esophageal cancer. Of the 57 lesions with final cytopathological results, the SUVmax of malignant lesions (mean: 7.62 ± 5.22, range: 1.7−24) was significantly higher than that of benign lesions (mean: 4.05 ± 2.58, range: 1.0−12.9) (p = 0.001). The diagnostic performance of subsequent US in all ITLs with cytopathological results revealed 86.4% (19/22) sensitivity, 71.4% (25/35) specificity, 65.5% (19/29) PPV, and 89.3% (25/28) NPV to detect malignancy (Table 3). Of probable benign lesions assessed by PET/CT (n = 9), US revealed 100% (9/9) specificity and 100% (9/9) NPV and had complete agreement with the final result. Four of nine lesions revealed diffuse and bilateral 18F-FDG uptake, and five lesions revealed focal low attenuated nodules without 18F-FDG uptake, which presented an SUVmax < 2.9 in

Note.-US = ultrasound

all cases (Figs. 2, 3). Of the suspicious malignant lesions assessed

rate between US-performed group (26%, 20/78) and US-not

(9/10) specificity, 75% (9/12) PPV, and 90% (9/10) NPV. Of 22

performed group (32%, 47/148) was not significantly different

patients, 21 revealed focal 18F-FDG uptake in unilateral lobes.

(p = 0.421). Table 2 shows the origin of the primary non-thyroi-

The other patient, who had metastasis from esophageal cancer,

dal cancers with ITLs.

revealed multifocal 18F-FDG uptakes in bilateral lobes. Mean

by PET/CT (n = 22), US revealed 75% (9/12) sensitivity, 90%

Of the 78 patients in the US-performed group, 57 had cytopa-

SUVmax was 7.75 (range, 2.7−24). Of the undetermined lesions

thological results. Thirteen patients underwent total thyroidec-

assessed by PET/CT (n = 26), US revealed 100% (10/10) sensi-

tomy for primary thyroid cancers, and the remaining 44 pa-

tivity, 94% (15/16) specificity, 91% (10/11) PPV, and 100%

tients underwent US-FNA with clinical and radiologic follow-

(15/15) NPV, corresponding to excellent agreement with the fi-

up. The final cytopathological results revealed malignant thyroid

nal results (kappa value = 0.92).

cancers (n = 22; papillary carcinoma: 20, medullary carcinoma: one, metastasis: one) and benign lesions (n = 35; nodular hyperplasia: 22, lymphocytic thyroiditis: four, cyst: two, others: seven). The malignant rate in the US-performed group that had cytopa-

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DISCUSSION The incidence of ITLs detected on 18F-FDG PET/CT for paJ Korean Soc Radiol 2014;71(3):111-119

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Table 3. Diagnostic Performance of US to Differentiate Malignancy for Incidental Thyroid Lesions US

PET/CT Findings Probable benign (n = 9) Suspicious malignant (n = 22) Undetermined (n = 26) Overall (n = 57)

Sensitivity 75.0 (9/12) 100 (10/10) 86.4 (19/22)

Specificity 100 (9/9) 90.0 (9/10) 93.8 (15/16) 71.4 (25/35)

PPV 75.0 (9/12) 90.9 (10/11) 65.5 (19/29)

NPV 100 (9/9) 90.0 (9/10) 100 (15/15) 89.3 (25/28)

Note.-NPV = negative predictive value, PET/CT = positron emission tomography/computed tomography, PPV = positive predictive value, US = ultrasound

B

A C Fig. 2. A 59-year-old female with sarcoma in the right pulmonary artery. The 18F-FDG PET/CT reveals a 2 cm low-attenuated nodule (arrowhead) with no uptake in the left lower thyroid lobe (A). Ultrasonograms show a smooth solid and cystic nodule (arrows) in the inferior pole of the left thyroid gland, which was diagnosed as a probably benign nodule (B: axial scan, C: longitudinal scan). Nodular hyperplasia was confirmed by USguided fine needle aspiration. Note.-PET/CT = positron emission tomography/computed tomography, US = ultrasound, 18F-FDG = 18F-fluorodeoxyglucose

tients with non-thyroid cancer was 8.4%, which was similar to the

subjects (2.6%) (6). Rheingold et al. (12) suggested that a history

9% reported in a previous study that investigated both focal and

of malignancy could be one of the major risk factors for develop-

diffuse F-FDG uptake lesions in thyroid gland (3). The inci-

ing another kind of malignancy. The reason that the incidence of

dence of thyroid incidentalomas (focal lesions) was 5.3% in our

thyroid incidentalomas in the present study was relatively higher

study, which was slightly higher than the 1.2−4.3% in other re-

was due to the population of only patients with primary malig-

ports in both patients with malignancies and healthy subjects (8-

nancies, compared to including healthy subjects.

18

11). It seemed that this difference resulted from the population in

In the present study, the incidence of malignant ITLs detected

the present study, which included only patients with nonthyroidal

on 18F-FDG PET/CT was 22 (39%) of 57 patients who had final

malignancies, and previous studies. The prevalence of thyroid in-

cytopathology. Other investigations revealed that it ranges from

cidentalomas detected on F-FDG PET/CT in patients with sus-

27% to 72% (4, 6, 9, 11, 13-15). Most of the 22 patients with ma-

pected or known cancer (4.1%) was higher than that in healthy

lignancies had primary thyroid carcinomas (20 papillary carcino-

18

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B

A C Fig. 3. A 47-year-old female with lung cancer. The 18F-FDG PET/CT reveals a 1 cm low-attenuated nodule (arrowhead) with mild uptake (SUV: 4.1) in the right thyroid lobe, which was diagnosed as a undetermined lesion (A). A 0.7 cm irregular hypoechoic nodule (arrow) with several microcalcifications is demonstrated on ultrasound, which was considered suspicion for malignancy (B: axial scan, C: oblique scan). Papillary thyroid carcinoma was confirmed by total thyroidectomy. Note.-PET/CT = positron emission tomography/computed tomography, SUV = standardized uptake value, 18F-FDG = 18F-fluorodeoxyglucose

mas and one medullary carcinoma), but the other one had me-

study, 21 primary thyroid cancers of 22 ITLs proven to be malig-

tastasis arising from esophageal cancer. Most malignant nodules

nant had focal uptake (unilateral uptake in 18 patients and bilat-

detected on F-FDG PET/CT were well-differentiated papillary

eral in three patients). The other of the 22 lesions was a metasta-

carcinomas, as reported by Deandreis et al. (5) and Pagano et al.

sis arising from esophageal cancer, which presented as diffuse

(16). Our study had no discrepancies to previously reported

and bilateral uptake in the thyroid gland, although US suggested

studies, although the healthy population was excluded in the

bilateral aggressive masses. Because all primary thyroid cancers

present study.

revealed focal uptake, we excluded primary thyroid cancers

18

Most researchers evaluate focal or diffuse uptake, unilateral or

from incidental thyroid lesions with diffuse and bilateral uptake.

bilateral uptake, and the SUVmax value to distinguish malig-

However, diffuse and bilateral uptake should be handled vigi-

nant from benign disease for ITLs on F-FDG PET/CT (4, 11,

lantly in patients with non-thyroid cancer because this finding

13, 16). ITLs detected by PET/CT had diffuse or focal F-FDG

can indicate metastasis.

18

18

uptake patterns. The diffuse uptake pattern is more frequently

Because the mean SUVmax value of malignant lesions was

benign disease, such as thyroiditis, nodular goiter, or Grave’s dis-

higher than that of benign lesions in the current study, we purport

ease (16). Focal uptake of thyroid incidentalomas is clinically

that the SUVmax value can help distinguish malignant lesions

more significant due to its high risk of malignancy, including

from benign. Cohen et al. (9) reported that the average SUVmax

primary thyroid cancer and metastasis (6, 9, 14, 15). The risk of

in malignant lesions (6.92 ± 1.54) was higher than that in benign

malignancy was extremely low (1.4%) in patients with diffuse or

lesions (3.37 ± 0.21). In another study, the diagnostic accuracy of

bilateral uptake on PET scans, while focal or unilateral uptake

SUVmax using a 4.2 cut-off value was 69.5%, without adding oth-

revealed a higher risk (15%) of malignancy (11). In the present

er imaging findings (3). In contrast, the SUVmax between benign

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and malignant thyroid nodules was not significantly different in

correlation among CT, sonography, and pathology. AJR Am

one study, although the average SUVmax of the malignant thyroid

J Roentgenol 2006;187:1349-1356

lesions was higher than that of benign thyroid lesions (4). The American Thyroid Association guidelines recommend

2. Bae JS, Chae BJ, Park WC, Kim JS, Kim SH, Jung SS, et al. Incidental thyroid lesions detected by FDG-PET/CT: prevalence

that diagnostic thyroid US should be performed for thyroid in-

and risk of thyroid cancer. World J Surg Oncol 2009;7:63

cidentalomas detected on F-FDG PET/CT (17). According to

3. Kang BJ, O JH, Baik JH, Jung SL, Park YH, Chung SK. Inci-

the recommendations with consensus among the American As-

dental thyroid uptake on F-18 FDG PET/CT: correlation with

sociation of Clinical Endocrinologists, Associazione Medici En-

ultrasonography and pathology. Ann Nucl Med 2009;23:

docrinologi, and the European Thyroid Association Medical

729-737

18

guidelines, a US evaluation should be conducted because of un-

4. Kwak JY, Kim EK, Yun M, Cho A, Kim MJ, Son EJ, et al. Thy-

certain risk of malignancy of thyroid incidentaloma (18). How-

roid incidentalomas identified by 18F-FDG PET: sonographic

ever, subsequent US had no additional diagnostic value for ITLs

correlation. AJR Am J Roentgenol 2008;191:598-603

with probable benign findings on F-FDG PET/CT in our study.

5. Deandreis D, Al Ghuzlan A, Auperin A, Vielh P, Caillou B,

Of 26 patients with undetermined findings on 18F-FDG PET/

Chami L, et al. Is (18)F-fluorodeoxyglucose-PET/CT useful

CT, the diagnostic performance of US showed excellent agree-

for the presurgical characterization of thyroid nodules with

ment with the final cytopathological results. The probability

indeterminate fine needle aspiration cytology? Thyroid

(13.2%) of malignancy was much lower than when the US find-

2012;22:165-172

18

ings appeared benign, as compared with significantly higher

6. Choi JY, Lee KS, Kim HJ, Shim YM, Kwon OJ, Park K, et al.

probability (75.5%) of malignance when the US findings were

Focal thyroid lesions incidentally identified by integrated

suspicious for malignant (4). Therefore, subsequent US can pro-

18F-FDG PET/CT: clinical significance and improved char-

vide additional diagnostic value when ITLs have undetermined findings on 18F-FDG PET/CT.

acterization. J Nucl Med 2006;47:609-615 7. Moon WJ, Baek JH, Jung SL, Kim DW, Kim EK, Kim JY, et al.

There are several limitations in this study. First, this study had

Ultrasonography and the ultrasound-based management

selection bias to evaluate diagnostic performances of F-FDG

of thyroid nodules: consensus statement and recommen-

PET/CT and US because only patients who underwent US-FNA

dations. Korean J Radiol 2011;12:1-14

18

or surgery were included. Second, the 3-year survival rate be-

8. Chen YK, Ding HJ, Chen KT, Chen YL, Liao AC, Shen YY, et

tween US-performed and US-not performed groups may not

al. Prevalence and risk of cancer of focal thyroid inciden-

have been sufficient to evaluate long-term mortality rates of the

taloma identified by 18F-fluorodeoxyglucose positron

patients. Third, we could not define criteria for subsequent US

emission tomography for cancer screening in healthy sub-

indications in this study because the 18F-FDG PET/CT and the

jects. Anticancer Res 2005;25:1421-1426

US results were retrospectively analyzed. Large prospective studies will need to solve the limitations of the present study. In conclusion, ITLs detected on F-FDG PET/CT did not af18

fect patient prognosis whether US was performed or not. Because

9. Cohen MS, Arslan N, Dehdashti F, Doherty GM, Lairmore TC, Brunt LM, et al. Risk of malignancy in thyroid incidentalomas identified by fluorodeoxyglucose-positron emission tomography. Surgery 2001;130:941-946

subsequent US has no additional diagnostic value in ITLs with

10. Kim SJ, Kim BH, Jeon YK, Kim SS, Kim IJ. Limited diagnos-

probable benign findings on F-FDG PET/CT, it may be unnec-

tic and predictive values of dual-time-point 18F FDG PET/

essary for ITLs with benign findings on PET/CT.

CT for differentiation of incidentally detected thyroid

18

nodules. Ann Nucl Med 2011;25:347-353

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high prevalence of malignancy in thyroid PET incidentalo-

Nodules. Endocr Pract 2010;16 Suppl 1:1-43

ma. Laryngoscope 2005;115:1074-1078

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비갑상선암 환자에서 시행한 18F-Fluorodeoxyglucose Positron Emission Tomography/CT에서 발견된 갑상선 우연종에 대한 초음파의 임상적 가치에 대한 연구1 이광희1,2 · 신정희1 · 한부경1 · 고은영1 · 고은숙1 · 한수연1 · 최준영3 목적: 비갑상선암을 가진 환자에게 촬영한 positron emission tomography/computed tomography (이하 PET/CT)에서 발견된 갑상선 우연종에 대한 초음파의 임상적 가치에 대해서 평가하는 것이다. 대상과 방법: 2703명의 비갑상선암을 가진 환자에게 시행한 3226 PET/CT 검사에서 후향적으로 갑상선 우연종을 검색 하였다. 대상 환자를 초음파 시행군과 비시행군으로 나누었다. PET/CT의 소견에 따라 초음파에서 암을 진단할 수 있는 능력을 평가하였다. 결과: 비갑상선암 환자에게 발견된 갑상선 우연종의 빈도는 8.4%였다(226/2703). 초음파를 시행한 군과 시행하지 않 은 군 사이에 3년 사망률에는 차이가 없었다. 갑상선 우연종의 암의 빈도는 39%였다(22/57). 모든 암은 한 명의 전이암 과 한 명의 수질암을 제외하고 모두 유두암이었다. 초음파의 진단율은 87% 민감도, 66% 특이도, 66% 양성예측도, 89% 음성예측도를 나타내었다. 양성 PET/CT 소견을 보인 우연종에서 초음파의 진단율은 100% 특이도, 100% 음성예측도를 보였고, 악성 PET/CT 소견을 보인 우연종에서 초음파의 진단율은 75% 민감도, 90% 특이도, 90% 양성예측도, 75% 음 성예측도를 보였다. 결론: 갑상선 우연종에서 초음파의 시행여부는 환자의 예후에 영향을 주지 않는다. 우연종이 PET/CT에서 양성 소견을 보일 때에는 초음파의 시행이 불필요할 수 있다. 성균관대학교 의과대학 삼성서울병원 1영상의학과, 3핵의학과, 2인제대학교 의과대학 해운대백병원 영상의학과

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