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

Affiliations
  • 1Department of Radiology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea. jhshin11@skku.edu
  • 2Department of Radiology, Haeundae Paik Hospital, Inje University College of Medicine, Busan, Korea.
  • 3Department of Nuclear Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.

Abstract

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.


MeSH Terms

Electrons*
Humans
Incidence
Mortality
Neoplasm Metastasis
Positron-Emission Tomography
Positron-Emission Tomography and Computed Tomography
Prognosis
Retrospective Studies
Sensitivity and Specificity
Thyroid Diseases
Thyroid Gland*
Ultrasonography*

Figure

  • 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 = 18F-fluorodeoxyglucose

  • 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 US-guided fine needle aspiration. Note.-PET/CT = positron emission tomography/computed tomography, US = ultrasound, 18F-FDG = 18F-fluorodeoxyglucose

  • 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


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