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FDG-PET/CT pitfalls in oncological head and neck imaging.

Purohit BS, Ailianou A, Dulguerov N, Becker CD, Ratib O, Becker M - Insights Imaging (2014)

Bottom Line: The commonly encountered false-positive PET/CT interpretation pitfalls are due to high FDG uptake by physiological causes, benign thyroid nodules, unilateral cranial nerve palsy and increased FDG uptake due to inflammation, recent chemoradiotherapy and surgery.False-negative findings are caused by lesion vicinity to structures with high glucose metabolism, obscuration of FDG uptake by dental hardware, inadequate PET scanner resolution and inherent low FDG-avidity of some tumours.The interpreting physician must be aware of these unusual patterns of FDG uptake, as well as limitations of PET/CT as a modality, in order to avoid overdiagnosis of benign conditions as malignancy, as well as missing out on actual pathology. • Knowledge of key imaging features of physiological and non-physiological FDG uptake is essential for the interpretation of head and neck PET/CT studies. • Precise anatomical evaluation and correlation with contrast-enhanced CT, US or MRI avoid PET/CT misinterpretation. • Awareness of unusual FDG uptake patterns avoids overdiagnosis of benign conditions as malignancy.

View Article: PubMed Central - PubMed

Affiliation: Department of Imaging, Division of Radiology, Geneva University Hospital, Rue Gabrielle Perret Gentil 4, 1211, Geneva 14, Switzerland.

ABSTRACT

Objectives: Positron emission tomography-computed tomography (PET/CT) with fluorine-18-fluorodeoxy-D-glucose (FDG) has evolved from a research modality to an invaluable tool in head and neck cancer imaging. However, interpretation of FDG PET/CT studies may be difficult due to the inherently complex anatomical landmarks, certain physiological variants and unusual patterns of high FDG uptake in the head and neck. The purpose of this article is to provide a comprehensive approach to key imaging features and interpretation pitfalls of FDG-PET/CT of the head and neck and how to avoid them.

Methods: We review the pathophysiological mechanisms leading to potentially false-positive and false-negative assessments, and we discuss the complementary use of high-resolution contrast-enhanced head and neck PET/CT (HR HN PET/CT) and additional cross-sectional imaging techniques, including ultrasound (US) and magnetic resonance imaging (MRI).

Results: The commonly encountered false-positive PET/CT interpretation pitfalls are due to high FDG uptake by physiological causes, benign thyroid nodules, unilateral cranial nerve palsy and increased FDG uptake due to inflammation, recent chemoradiotherapy and surgery. False-negative findings are caused by lesion vicinity to structures with high glucose metabolism, obscuration of FDG uptake by dental hardware, inadequate PET scanner resolution and inherent low FDG-avidity of some tumours.

Conclusions: The interpreting physician must be aware of these unusual patterns of FDG uptake, as well as limitations of PET/CT as a modality, in order to avoid overdiagnosis of benign conditions as malignancy, as well as missing out on actual pathology.

Teaching points: • Knowledge of key imaging features of physiological and non-physiological FDG uptake is essential for the interpretation of head and neck PET/CT studies. • Precise anatomical evaluation and correlation with contrast-enhanced CT, US or MRI avoid PET/CT misinterpretation. • Awareness of unusual FDG uptake patterns avoids overdiagnosis of benign conditions as malignancy.

No MeSH data available.


Related in: MedlinePlus

a Axial PET/CT image demonstrates asymmetrical FDG uptake of the tonsillar fossae (arrowhead) and parotid glands (increased uptake on the left, arrow) in a patient previously irradiated for SCC of the right base of the tongue with sparing of the left side. Note increased FDG uptake of the non-irradiated left parotid gland (arrow) and fatty infiltration of the irradiated right parotid gland (asterisk). b Corresponding axial contrast-enhanced T1-weighted image shows no pathological findings in the left tonsillar fossa (arrowhead) and left parotid gland (arrow). Note atrophy and fatty infiltration of the right parotid gland (asterisk). c Corresponding b1,000 DW MR image reveals physiological hyperintensity in the tonsillar fossae more pronounced on left (arrowhead) compared with the right (arrow) due to normal lymphoid tissue on the left and atrophy of lymphoid tissue on the right. d Corresponding ADC map showing physiologically low ADC values on the left (arrowhead) due to normal lymphoid tissue. Dashed arrows point at radiation port on the right
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Fig4: a Axial PET/CT image demonstrates asymmetrical FDG uptake of the tonsillar fossae (arrowhead) and parotid glands (increased uptake on the left, arrow) in a patient previously irradiated for SCC of the right base of the tongue with sparing of the left side. Note increased FDG uptake of the non-irradiated left parotid gland (arrow) and fatty infiltration of the irradiated right parotid gland (asterisk). b Corresponding axial contrast-enhanced T1-weighted image shows no pathological findings in the left tonsillar fossa (arrowhead) and left parotid gland (arrow). Note atrophy and fatty infiltration of the right parotid gland (asterisk). c Corresponding b1,000 DW MR image reveals physiological hyperintensity in the tonsillar fossae more pronounced on left (arrowhead) compared with the right (arrow) due to normal lymphoid tissue on the left and atrophy of lymphoid tissue on the right. d Corresponding ADC map showing physiologically low ADC values on the left (arrowhead) due to normal lymphoid tissue. Dashed arrows point at radiation port on the right

Mentions: FDG is physiologically taken up by the salivary glands and excreted into saliva. Low to high FDG symmetrical uptake is noted in the parotid and submandibular glands (Fig. 3). Benign conditions like sarcoidosis, tuberculosis, viral infections, bacterial infections, obstructive lithiasis and radiation-induced sialadenitis can also cause increased FDG uptake in the salivary glands. Asymmetrical salivary gland uptake in the floor of the mouth can mimic focal areas of oral cavity malignancy. Asymmetrical submandibular gland uptake can be seen in patients who have undergone surgical removal of a gland with contralateral hypertrophy and in patients who have undergone unilateral radiation therapy [2–4, 6–9] (Fig. 4). This focal asymmetrical uptake may occasionally mimic metastatic adenopathy at level IB or II [4]. While symmetrical diffuse uptake in the salivary glands may be physiological (Fig. 3), focal, asymmetrical uptake may also be suggestive of FDG-avid benign or malignant salivary gland tumours like Warthin tumour, pleomorphic adenoma, primary parotid lymphoma or intraparotid lymph node metastasis from skin cancer. The SUVs of most malignant parotid tumours are significantly higher than those of benign lesions. However, some benign tumours may show very high FDG uptake (typically Warthin tumours), thereby mimicking malignant disease, while a few malignant parotid gland neoplasms (typically adenoid cystic carcinomas, low grade mucoepidermoid carcinoma or necrotic SCC) may have no significant FDG avidity [2, 4, 9, 18–20]. Also, some studies show that high-grade salivary gland malignancies are associated with higher SUVs compared with low grade malignancies [20]. Smaller salivary gland tumours may be missed on CECT. Hence, in the presence of a focal asymmetrical FDG uptake, further evaluation with ultrasound (US)/US-guided fine needle aspiration cytology (US FNAC) and/or MRI is often mandatory to reach the definitive diagnosis [7, 18–20]. Due to wide availability, low cost and high diagnostic accuracy, US is commonly used as a problem-solving modality for the evaluation of salivary gland conditions [21–23]. Many authors advocate the use of US FNAC for the pre-operative evaluation of parotid masses due to its good diagnostic accuracy. One study [24] shows that the positive predictive value of US FNAC for diagnosing parotid malignancy was 84.6 % and the negative predictive value was 96.4 %. Although MRI is mostly used for the precise assessment of tumour spread, it can also be used as an adjunct to differentiate between benign and malignant salivary gland tumours. Malignant salivary gland tumours are often associated with ill-defined margins, low T2 signal due to high cellularity, perineural spread most often along the facial nerve (when originating in the parotid gland), invasion of the mandible, skull base, subcutaneous fat or skin and lymph node metastases [25]. Nevertheless, these signs may be absent in small-sized or well-differentiated malignant tumours, making differentiation from benign lesions difficult. Quantitative analysis with DWI may be of help as the mean apparent diffusion coefficient (ADC) of benign tumours (1.72 × 10−3 mm2/s is often higher than that of malignant tumours (1.05 × 10−3 mm2/s (P < 0.001) [26], with the exception of Whartin tumours, which typically show very low ADC values.Fig. 3


FDG-PET/CT pitfalls in oncological head and neck imaging.

Purohit BS, Ailianou A, Dulguerov N, Becker CD, Ratib O, Becker M - Insights Imaging (2014)

a Axial PET/CT image demonstrates asymmetrical FDG uptake of the tonsillar fossae (arrowhead) and parotid glands (increased uptake on the left, arrow) in a patient previously irradiated for SCC of the right base of the tongue with sparing of the left side. Note increased FDG uptake of the non-irradiated left parotid gland (arrow) and fatty infiltration of the irradiated right parotid gland (asterisk). b Corresponding axial contrast-enhanced T1-weighted image shows no pathological findings in the left tonsillar fossa (arrowhead) and left parotid gland (arrow). Note atrophy and fatty infiltration of the right parotid gland (asterisk). c Corresponding b1,000 DW MR image reveals physiological hyperintensity in the tonsillar fossae more pronounced on left (arrowhead) compared with the right (arrow) due to normal lymphoid tissue on the left and atrophy of lymphoid tissue on the right. d Corresponding ADC map showing physiologically low ADC values on the left (arrowhead) due to normal lymphoid tissue. Dashed arrows point at radiation port on the right
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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Fig4: a Axial PET/CT image demonstrates asymmetrical FDG uptake of the tonsillar fossae (arrowhead) and parotid glands (increased uptake on the left, arrow) in a patient previously irradiated for SCC of the right base of the tongue with sparing of the left side. Note increased FDG uptake of the non-irradiated left parotid gland (arrow) and fatty infiltration of the irradiated right parotid gland (asterisk). b Corresponding axial contrast-enhanced T1-weighted image shows no pathological findings in the left tonsillar fossa (arrowhead) and left parotid gland (arrow). Note atrophy and fatty infiltration of the right parotid gland (asterisk). c Corresponding b1,000 DW MR image reveals physiological hyperintensity in the tonsillar fossae more pronounced on left (arrowhead) compared with the right (arrow) due to normal lymphoid tissue on the left and atrophy of lymphoid tissue on the right. d Corresponding ADC map showing physiologically low ADC values on the left (arrowhead) due to normal lymphoid tissue. Dashed arrows point at radiation port on the right
Mentions: FDG is physiologically taken up by the salivary glands and excreted into saliva. Low to high FDG symmetrical uptake is noted in the parotid and submandibular glands (Fig. 3). Benign conditions like sarcoidosis, tuberculosis, viral infections, bacterial infections, obstructive lithiasis and radiation-induced sialadenitis can also cause increased FDG uptake in the salivary glands. Asymmetrical salivary gland uptake in the floor of the mouth can mimic focal areas of oral cavity malignancy. Asymmetrical submandibular gland uptake can be seen in patients who have undergone surgical removal of a gland with contralateral hypertrophy and in patients who have undergone unilateral radiation therapy [2–4, 6–9] (Fig. 4). This focal asymmetrical uptake may occasionally mimic metastatic adenopathy at level IB or II [4]. While symmetrical diffuse uptake in the salivary glands may be physiological (Fig. 3), focal, asymmetrical uptake may also be suggestive of FDG-avid benign or malignant salivary gland tumours like Warthin tumour, pleomorphic adenoma, primary parotid lymphoma or intraparotid lymph node metastasis from skin cancer. The SUVs of most malignant parotid tumours are significantly higher than those of benign lesions. However, some benign tumours may show very high FDG uptake (typically Warthin tumours), thereby mimicking malignant disease, while a few malignant parotid gland neoplasms (typically adenoid cystic carcinomas, low grade mucoepidermoid carcinoma or necrotic SCC) may have no significant FDG avidity [2, 4, 9, 18–20]. Also, some studies show that high-grade salivary gland malignancies are associated with higher SUVs compared with low grade malignancies [20]. Smaller salivary gland tumours may be missed on CECT. Hence, in the presence of a focal asymmetrical FDG uptake, further evaluation with ultrasound (US)/US-guided fine needle aspiration cytology (US FNAC) and/or MRI is often mandatory to reach the definitive diagnosis [7, 18–20]. Due to wide availability, low cost and high diagnostic accuracy, US is commonly used as a problem-solving modality for the evaluation of salivary gland conditions [21–23]. Many authors advocate the use of US FNAC for the pre-operative evaluation of parotid masses due to its good diagnostic accuracy. One study [24] shows that the positive predictive value of US FNAC for diagnosing parotid malignancy was 84.6 % and the negative predictive value was 96.4 %. Although MRI is mostly used for the precise assessment of tumour spread, it can also be used as an adjunct to differentiate between benign and malignant salivary gland tumours. Malignant salivary gland tumours are often associated with ill-defined margins, low T2 signal due to high cellularity, perineural spread most often along the facial nerve (when originating in the parotid gland), invasion of the mandible, skull base, subcutaneous fat or skin and lymph node metastases [25]. Nevertheless, these signs may be absent in small-sized or well-differentiated malignant tumours, making differentiation from benign lesions difficult. Quantitative analysis with DWI may be of help as the mean apparent diffusion coefficient (ADC) of benign tumours (1.72 × 10−3 mm2/s is often higher than that of malignant tumours (1.05 × 10−3 mm2/s (P < 0.001) [26], with the exception of Whartin tumours, which typically show very low ADC values.Fig. 3

Bottom Line: The commonly encountered false-positive PET/CT interpretation pitfalls are due to high FDG uptake by physiological causes, benign thyroid nodules, unilateral cranial nerve palsy and increased FDG uptake due to inflammation, recent chemoradiotherapy and surgery.False-negative findings are caused by lesion vicinity to structures with high glucose metabolism, obscuration of FDG uptake by dental hardware, inadequate PET scanner resolution and inherent low FDG-avidity of some tumours.The interpreting physician must be aware of these unusual patterns of FDG uptake, as well as limitations of PET/CT as a modality, in order to avoid overdiagnosis of benign conditions as malignancy, as well as missing out on actual pathology. • Knowledge of key imaging features of physiological and non-physiological FDG uptake is essential for the interpretation of head and neck PET/CT studies. • Precise anatomical evaluation and correlation with contrast-enhanced CT, US or MRI avoid PET/CT misinterpretation. • Awareness of unusual FDG uptake patterns avoids overdiagnosis of benign conditions as malignancy.

View Article: PubMed Central - PubMed

Affiliation: Department of Imaging, Division of Radiology, Geneva University Hospital, Rue Gabrielle Perret Gentil 4, 1211, Geneva 14, Switzerland.

ABSTRACT

Objectives: Positron emission tomography-computed tomography (PET/CT) with fluorine-18-fluorodeoxy-D-glucose (FDG) has evolved from a research modality to an invaluable tool in head and neck cancer imaging. However, interpretation of FDG PET/CT studies may be difficult due to the inherently complex anatomical landmarks, certain physiological variants and unusual patterns of high FDG uptake in the head and neck. The purpose of this article is to provide a comprehensive approach to key imaging features and interpretation pitfalls of FDG-PET/CT of the head and neck and how to avoid them.

Methods: We review the pathophysiological mechanisms leading to potentially false-positive and false-negative assessments, and we discuss the complementary use of high-resolution contrast-enhanced head and neck PET/CT (HR HN PET/CT) and additional cross-sectional imaging techniques, including ultrasound (US) and magnetic resonance imaging (MRI).

Results: The commonly encountered false-positive PET/CT interpretation pitfalls are due to high FDG uptake by physiological causes, benign thyroid nodules, unilateral cranial nerve palsy and increased FDG uptake due to inflammation, recent chemoradiotherapy and surgery. False-negative findings are caused by lesion vicinity to structures with high glucose metabolism, obscuration of FDG uptake by dental hardware, inadequate PET scanner resolution and inherent low FDG-avidity of some tumours.

Conclusions: The interpreting physician must be aware of these unusual patterns of FDG uptake, as well as limitations of PET/CT as a modality, in order to avoid overdiagnosis of benign conditions as malignancy, as well as missing out on actual pathology.

Teaching points: • Knowledge of key imaging features of physiological and non-physiological FDG uptake is essential for the interpretation of head and neck PET/CT studies. • Precise anatomical evaluation and correlation with contrast-enhanced CT, US or MRI avoid PET/CT misinterpretation. • Awareness of unusual FDG uptake patterns avoids overdiagnosis of benign conditions as malignancy.

No MeSH data available.


Related in: MedlinePlus