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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 shows asymmetric uptake in the nasopharynx (arrowhead) and expected high uptake in the explored hindbrain. A lytic lesion in the clivus with well-defined sclerotic borders and without FDG uptake is also detected (arrow). The remaining of the total body PET/CT was normal. b Corresponding axial contrast-enhanced T1weighted MR image obtained in the same patient illustrates an infiltrative, poorly delineated tumour invading the clivus, the right jugular fossa, the right petrous apex and the brainstem (arrows), not revealed by PET/CT. Subsequent biopsy of the clivus, intracranially and of the nasopharynx showed a primary adenocarcinoma of the skull base. The increased FDG uptake in the left nasopharynx corresponds to tumour invasion of the longus colli muscle. Due to intratumoral areas with variable FDG avidity and due to tumor vicinity to the highly metabolic brain parenchyma, this lesion is less well depicted by PET/CT than MRI
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Fig16: a Axial PET/CT image shows asymmetric uptake in the nasopharynx (arrowhead) and expected high uptake in the explored hindbrain. A lytic lesion in the clivus with well-defined sclerotic borders and without FDG uptake is also detected (arrow). The remaining of the total body PET/CT was normal. b Corresponding axial contrast-enhanced T1weighted MR image obtained in the same patient illustrates an infiltrative, poorly delineated tumour invading the clivus, the right jugular fossa, the right petrous apex and the brainstem (arrows), not revealed by PET/CT. Subsequent biopsy of the clivus, intracranially and of the nasopharynx showed a primary adenocarcinoma of the skull base. The increased FDG uptake in the left nasopharynx corresponds to tumour invasion of the longus colli muscle. Due to intratumoral areas with variable FDG avidity and due to tumor vicinity to the highly metabolic brain parenchyma, this lesion is less well depicted by PET/CT than MRI

Mentions: Proximity of a pathological lesion to another FDG-avid lesion or normal structure with high FDG uptake may lead to a false-negative diagnosis. This is most commonly seen in skull base tumours in the vicinity of highly metabolic brain parenchyma or in small oral cavity tumours close to the tonsils, which show high physiological FDG uptake (see above) [3, 4, 9, 33, 68]. In the orbit, the high metabolic activity of extraocular muscles acts as a further confounding factor [69]. In addition, abnormalities of the skull base and orbit tend to be overlooked on head and neck PET/CT examinations also because they are often subtle and they are typically at the edge of the field of view [69]. Detailed anatomic evaluation of the CT part of PET/CT is essential for the detection of subtle obscuration of fat planes beneath the skull base or bony erosion of skull-base foramina. Nevertheless, an additional MRI examination (Fig. 16) is often necessary for the precise evaluation of tumour spread in these specific regions. A common example of this pitfall occurs in the evaluation of primary nasopharyngeal carcinoma with FDG-PET/CT. FDG PET/CT is known to underestimate perineural spread, tumour involvement of the skull base and cavernous sinuses compared with MRI, due to the surrounding ‘shine through effect of FDG’ around the tumour and because of the inferior conspicuity of these conditions on CECT compared with MRI [4, 33, 70]. However, the higher FDG accumulation in the tumour as compared to that in the adjacent grey matter and changing the window and level settings on PET/CT scans may help to pick up the lesion in some cases [48, 49]. Due to the close vicinity of retropharyngeal lymph nodes to the nasopharynx, detection of retropharyngeal nodal metastases with PET/CT may be impossible and correlation with MRI is necessary for correct tumour staging [4, 33, 70] (Fig. 17). The recent introduction of hybrid PET/MRI systems is expected to facilitate image interpretation in these particular situations [5, 48–51]. Boss et al. have shown promising results for the evaluation of skull base and suprahyoid neck tumours using PET/MRI hybrid systems [49], and Vargas et al. [50] and Varoquaux et al. [51] reported excellent PET/MRI image quality and lesion conspicuity in head and neck cancer patients. Nevertheless, PET/MRI systems are still not widely available [5] and ongoing research will clarify potential future applications in the head and neck.Fig. 14


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 shows asymmetric uptake in the nasopharynx (arrowhead) and expected high uptake in the explored hindbrain. A lytic lesion in the clivus with well-defined sclerotic borders and without FDG uptake is also detected (arrow). The remaining of the total body PET/CT was normal. b Corresponding axial contrast-enhanced T1weighted MR image obtained in the same patient illustrates an infiltrative, poorly delineated tumour invading the clivus, the right jugular fossa, the right petrous apex and the brainstem (arrows), not revealed by PET/CT. Subsequent biopsy of the clivus, intracranially and of the nasopharynx showed a primary adenocarcinoma of the skull base. The increased FDG uptake in the left nasopharynx corresponds to tumour invasion of the longus colli muscle. Due to intratumoral areas with variable FDG avidity and due to tumor vicinity to the highly metabolic brain parenchyma, this lesion is less well depicted by PET/CT than MRI
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Related In: Results  -  Collection

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Fig16: a Axial PET/CT image shows asymmetric uptake in the nasopharynx (arrowhead) and expected high uptake in the explored hindbrain. A lytic lesion in the clivus with well-defined sclerotic borders and without FDG uptake is also detected (arrow). The remaining of the total body PET/CT was normal. b Corresponding axial contrast-enhanced T1weighted MR image obtained in the same patient illustrates an infiltrative, poorly delineated tumour invading the clivus, the right jugular fossa, the right petrous apex and the brainstem (arrows), not revealed by PET/CT. Subsequent biopsy of the clivus, intracranially and of the nasopharynx showed a primary adenocarcinoma of the skull base. The increased FDG uptake in the left nasopharynx corresponds to tumour invasion of the longus colli muscle. Due to intratumoral areas with variable FDG avidity and due to tumor vicinity to the highly metabolic brain parenchyma, this lesion is less well depicted by PET/CT than MRI
Mentions: Proximity of a pathological lesion to another FDG-avid lesion or normal structure with high FDG uptake may lead to a false-negative diagnosis. This is most commonly seen in skull base tumours in the vicinity of highly metabolic brain parenchyma or in small oral cavity tumours close to the tonsils, which show high physiological FDG uptake (see above) [3, 4, 9, 33, 68]. In the orbit, the high metabolic activity of extraocular muscles acts as a further confounding factor [69]. In addition, abnormalities of the skull base and orbit tend to be overlooked on head and neck PET/CT examinations also because they are often subtle and they are typically at the edge of the field of view [69]. Detailed anatomic evaluation of the CT part of PET/CT is essential for the detection of subtle obscuration of fat planes beneath the skull base or bony erosion of skull-base foramina. Nevertheless, an additional MRI examination (Fig. 16) is often necessary for the precise evaluation of tumour spread in these specific regions. A common example of this pitfall occurs in the evaluation of primary nasopharyngeal carcinoma with FDG-PET/CT. FDG PET/CT is known to underestimate perineural spread, tumour involvement of the skull base and cavernous sinuses compared with MRI, due to the surrounding ‘shine through effect of FDG’ around the tumour and because of the inferior conspicuity of these conditions on CECT compared with MRI [4, 33, 70]. However, the higher FDG accumulation in the tumour as compared to that in the adjacent grey matter and changing the window and level settings on PET/CT scans may help to pick up the lesion in some cases [48, 49]. Due to the close vicinity of retropharyngeal lymph nodes to the nasopharynx, detection of retropharyngeal nodal metastases with PET/CT may be impossible and correlation with MRI is necessary for correct tumour staging [4, 33, 70] (Fig. 17). The recent introduction of hybrid PET/MRI systems is expected to facilitate image interpretation in these particular situations [5, 48–51]. Boss et al. have shown promising results for the evaluation of skull base and suprahyoid neck tumours using PET/MRI hybrid systems [49], and Vargas et al. [50] and Varoquaux et al. [51] reported excellent PET/MRI image quality and lesion conspicuity in head and neck cancer patients. Nevertheless, PET/MRI systems are still not widely available [5] and ongoing research will clarify potential future applications in the head and neck.Fig. 14

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