J Korean Soc Radiol.  2017 Feb;76(2):126-137. 10.3348/jksr.2017.76.2.126.

Benign Thyroid and Neck Lesions Mimicking Malignancy with False Positive Findings on Positron Emission Tomography-Computed Tomography

• Yoon YR
• Kim SY
• Lee SM
• Lee DY

• KMID: 2367860
• DOI: http://doi.org/10.3348/jksr.2017.76.2.126

Abstract

The increasing use of positron emission tomography-computed tomography (PET/CT) has led to the frequent detection of incidental thyroid and neck lesions with increased ¹â¸F-deoxyglucose (FDG) uptake. Although lesions with increased FDG uptake are commonly assumed to be malignant, benign lesions may also exhibit increased uptake. The purpose of this pictorial essay is to demonstrate that benign thyroid and neck lesions can produce false-positive findings on PET/CT, and to identify various difficulties in interpretation. It is crucial to be aware that differentiating between benign and malignant lesions is difficult in a considerable proportion of cases, when relying only on PET/CT findings. Correlation of PET/CT findings with additional imaging modalities is essential to avoid misdiagnosis.

MeSH Terms

Diagnostic Errors
Electrons*
Neck*
Positron-Emission Tomography
Positron-Emission Tomography and Computed Tomography
Thyroid Gland*
Thyroid Neoplasms

Figure

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  Fig. 1 Nodular hyperplasia, a 67-year-old woman with breast cancer. A. PET/CT transaxial fusion image shows focal FDG uptake in the right lobe of the thyroid gland (arrow) (SUVmax = 5.09). B. Ultrasonography image shows an oval shaped isoechoic nodule in the right thyroid lobe (arrow). FNA confirmed nodular hyperplasia. FDG = 18F-deoxyglucose, FNA = fine needle aspiration, PET/CT = positron emission tomography-computed tomography, SUV = standardized uptake value

• 

  Fig. 2 Hashimoto's thyroiditis, a 54-year-old woman, screening. A. PET/CT transaxial fusion image shows increased diffuse FDG uptake in both lobes of thyroid gland (arrows) (SUVmax = 4.2). B. Ultrasonography image shows heterogeneous parenchymal echogenicity with ill-defined oval hypoechoic nodules in the right lobe of the thyroid gland (arrow). FNA confirmed Hashimoto's thyroiditis. FDG = 18F-deoxyglucose, FNA = fine needle aspiration, PET/CT = positron emission tomography-computed tomography, SUV = standardized uptake value

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  Fig. 3 Subacute thyroiditis, a 62-year-old woman with stomach cancer. A. PET/CT transaxial fusion image shows increased diffuse FDG uptake in both lobes of the thyroid gland (arrows) (SUVmax = 3.47). B. Ultrasonography images show irregular margin and heterogeneous hypoechoic area in anterior portion of both lobes of the thyroid gland (arrows) with decreased vascularity on color Doppler ultrasonography (not shown). FNA confirmed subacute thyroiditis. FDG = 18F-deoxyglucose, FNA = fine needle aspiration, PET/CT = positron emission tomography-computed tomography, SUV = standardized uptake value

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  Fig. 4 Benign inflammation (tuberculous lymphadenopathy), a 75-year-old woman with cervical cancer. A. PET/CT transaxial fusion image shows increased focal nodular FDG uptake in right neck level IV (arrow) (SUVmax = 2.4). B. Ultrasonography image shows a small lymph node in the right neck with loss of fatty hilum (arrow). Biopsy confirmed tuberculosis. FDG = 18F-deoxyglucose, PET/CT = positron emission tomography-computed tomography, SUV = standardized uptake value

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  Fig. 5 Benign inflammation (reactive lymphadenopathy), a 69-year-old man with stomach cancer. A. PET/CT transaxial fusion image shows a lymph node in right supraclavicular area with increased FDG uptake (arrow) (SUVmax = 3.5). B. Ultrasonography image shows an enlarged lymph node in the right supraclavicular area with loss of fatty hilum (arrow). Biopsy confirmed reactive hyperplasia. FDG = 18F-deoxyglucose, PET/CT = positron emission tomography-computed tomography, SUV = standardized uptake value

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  Fig. 6 Traumatic neuroma, a 32-year-old man with total thyroidectomy for papillary thyroid cancer. A. PET/CT transaxial fusion image shows increased FDG uptake in the right neck (arrow) (SUVmax = 2.1). B. Ultrasonography image shows a spindle-shaped circumscribed heterogeneous isoechoic nodule in the right neck (arrow). An 18G core needle biopsy was performed and traumatic neuroma was confirmed. FDG = 18F-deoxyglucose, PET/CT = positron emission tomography-computed tomography, SUV = standardized uptake value

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  Fig. 7 Schwannoma, a 64-year-old woman with breast cancer. A. PET/CT transaxial fusion image shows increased focal nodular FDG uptake in the right neck (arrow) (SUVmax = 5.5). B. Ultrasonography image shows a circumscribed, oval, heterogeneous, hypoechoic nodule in the right neck (arrow). An 18G core needle biopsy confirmed schwannoma. FDG = 18F-deoxyglucose, PET/CT = positron emission tomography-computed tomography, SUV = standardized uptake value

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  Fig. 8 Foreign body granuloma, a 43-year-old woman with left hemithyroidectomy for left thyroid cancer. A. PET/CT transaxial fusion image shows increased focal nodular FDG uptake in the postoperative bed of the left anterior neck (arrow) (SUVmax = 2.9). B. Ultrasonography image shows a well-defined, round, isoechoic nodular lesion in the postoperative bed of the left anterior neck (arrow). An 18G core needle biopsy was performed, confirming foreign body granuloma. FDG = 18F-deoxyglucose, PET/CT = positron emission tomography-computed tomography, SUV = standardized uptake value

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  Fig. 9 Warthin's tumor, a 72-year-old man with supraglottic cancer. A. PET/CT transaxial fusion image shows increased focal nodular FDG uptake in the left parotid gland (arrow) (SUVmax=5.26). B. Ultrasonography image shows a well-defined, hypoechoic nodular lesion in the left parotid gland (arrow). An 18G core needle biopsy confirmed Warthin's tumor. FDG = 18F-deoxyglucose, PET/CT = positron emission tomography-computed tomography, SUV = standardized uptake value

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  Fig. 10 Inflammation after recent surgery, a 55-year-old man following wide excision and chemoradiotherapy for tongue cancer. A. PET/CT transaxial fusion image shows focal FDG uptake in the operation bed and left oropharynx (arrows) (SUVmax = 4.1). B. Contrast-enhanced axial CT image shows a peripherally enhanced lesion in the left oropharynx (arrow). Physical examination and pathology confirmed the absence of malignancy. FDG = 18F-deoxyglucose, PET/CT = positron emission tomography-computed tomography, SUV = standardized uptake value

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  Fig. 11 Inflammation after radiotherapy, a 61-year-old man following radiotherapy for glottic cancer. A. Initial PET/CT transaxial fusion image shows no definite FDG uptake in the anterior neck muscles. B. A 10-month follow-up PET/CT transaxial fusion image shows a newly developed increased diffuse FDG uptake in the muscles of the anterior neck (arrows) (SUVmax = 3.05). FDG = 18F-deoxyglucose, PET/CT = positron emission tomography-computed tomography, SUV = standardized uptake value

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