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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 intense FDG uptake in the right root of the tongue and floor of the mouth (asterisk) in a patient with recent surgical resection of recurrent SCC of the left hemitongue. b Corresponding axial non-contrast CT image confirms post-surgical architectural distortion without an obvious underlying mass lesion (asterisk) on the right. Corresponding axial T2W (c) and contrast-enhanced T1W (d) images reveal a linear band of low signal intensity scar tissue on the left (arrows). No tumour is seen on the right (asterisks). Muscle architecture in the right floor of the mouth appears normal on T2 but there is some diffuse muscular enhancement on the corresponding T1W image. Compensatory hyperactivity and post-surgical inflammatory findings due to contralateral scarring were considered as the cause of this unusually high FDG uptake. Follow-up of 2 years confirmed absence of recurrence
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Fig10: a Axial PET/CT image shows intense FDG uptake in the right root of the tongue and floor of the mouth (asterisk) in a patient with recent surgical resection of recurrent SCC of the left hemitongue. b Corresponding axial non-contrast CT image confirms post-surgical architectural distortion without an obvious underlying mass lesion (asterisk) on the right. Corresponding axial T2W (c) and contrast-enhanced T1W (d) images reveal a linear band of low signal intensity scar tissue on the left (arrows). No tumour is seen on the right (asterisks). Muscle architecture in the right floor of the mouth appears normal on T2 but there is some diffuse muscular enhancement on the corresponding T1W image. Compensatory hyperactivity and post-surgical inflammatory findings due to contralateral scarring were considered as the cause of this unusually high FDG uptake. Follow-up of 2 years confirmed absence of recurrence

Mentions: Depending on institutional choices, surgery may be preferentially performed in patients with advanced nodal disease, in patients with oral cavity cancers or in patients with recurrent disease after chemoradiation. Although the morphological changes are straightforward after radical or functional neck dissection, partial glossectomy and total or partial laryngectomy, interpretation of the post-surgical neck may be more complicated in cases with reconstructive procedures using grafts or flaps (free or pedicle) and in cases with combined surgery and chemoradiation. Due to the confusing surgical anatomy, recurrent tumours are more easily identified with PET/CT than with CT alone due to the increased focal uptake of recurrent disease. Nevertheless, after surgical removal of a gland or muscle the contralateral gland or muscle may show increased FDG uptake (Fig. 10) mimicking tumour recurrence and careful analysis of postoperative neck changes can help to solve this diagnostic dilemma. Post-surgical inflammatory oedema, scarring and granulation tissue can also cause increased FDG uptake making the interpretation of PET/CT studies very difficult in particular if the CT part of the PET/CT study comprises only a low dose CT for attenuation correction or if no CECT images are available (Fig. 10). Granulation tissue is the first step in wound healing and develops from connective tissue around the damaged area [52, 53]. It mainly contains inflammatory cells, fibroblasts, myofibroblasts and small vessels [52]. Over time, myofibroblasts and small vessels gradually disappear and granulation tissue evolves into immature and then mature scar. The mechanism responsible for this process is granulation tissue apoptosis, which mainly occurs between 20 and 25 days after injury, the fibroblastic apoptotic cells being continuously removed by macrophages [52]. Histological and morphometric studies have shown that the transformation of granulation tissue into scar tissue usually takes place within the first 2 months of injury [52], However, the duration of this process may vary depending on the amount of damaged tissue. As this transformation is a continuous process, there is a smooth transition between granulation tissue, early (immature) scar with limited amount of collagen and late (mature) scar with significant collagen deposition. Major FDG uptake, as seen on PET/CT images, is typically seen during the first weeks to months after surgery; it tends to decrease gradually over time. Post-surgical anatomical distortion can further increase the diagnostic dilemma in such cases. Therefore, it is generally recommended that the follow up PET/CT be performed at least 4–6 weeks after surgery after acute inflammation has subsided. Detailed knowledge of the previous surgical procedure and surgical complications (abscess, phlegmon, flap necrosis) helps to avoid diagnostic errors. Occasionally, to make the PET/CT image fusion precise, an additional MRI may be necessary to avoid misdiagnosis [1–4, 8, 42] (Fig. 10).Fig. 9


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 intense FDG uptake in the right root of the tongue and floor of the mouth (asterisk) in a patient with recent surgical resection of recurrent SCC of the left hemitongue. b Corresponding axial non-contrast CT image confirms post-surgical architectural distortion without an obvious underlying mass lesion (asterisk) on the right. Corresponding axial T2W (c) and contrast-enhanced T1W (d) images reveal a linear band of low signal intensity scar tissue on the left (arrows). No tumour is seen on the right (asterisks). Muscle architecture in the right floor of the mouth appears normal on T2 but there is some diffuse muscular enhancement on the corresponding T1W image. Compensatory hyperactivity and post-surgical inflammatory findings due to contralateral scarring were considered as the cause of this unusually high FDG uptake. Follow-up of 2 years confirmed absence of recurrence
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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Fig10: a Axial PET/CT image shows intense FDG uptake in the right root of the tongue and floor of the mouth (asterisk) in a patient with recent surgical resection of recurrent SCC of the left hemitongue. b Corresponding axial non-contrast CT image confirms post-surgical architectural distortion without an obvious underlying mass lesion (asterisk) on the right. Corresponding axial T2W (c) and contrast-enhanced T1W (d) images reveal a linear band of low signal intensity scar tissue on the left (arrows). No tumour is seen on the right (asterisks). Muscle architecture in the right floor of the mouth appears normal on T2 but there is some diffuse muscular enhancement on the corresponding T1W image. Compensatory hyperactivity and post-surgical inflammatory findings due to contralateral scarring were considered as the cause of this unusually high FDG uptake. Follow-up of 2 years confirmed absence of recurrence
Mentions: Depending on institutional choices, surgery may be preferentially performed in patients with advanced nodal disease, in patients with oral cavity cancers or in patients with recurrent disease after chemoradiation. Although the morphological changes are straightforward after radical or functional neck dissection, partial glossectomy and total or partial laryngectomy, interpretation of the post-surgical neck may be more complicated in cases with reconstructive procedures using grafts or flaps (free or pedicle) and in cases with combined surgery and chemoradiation. Due to the confusing surgical anatomy, recurrent tumours are more easily identified with PET/CT than with CT alone due to the increased focal uptake of recurrent disease. Nevertheless, after surgical removal of a gland or muscle the contralateral gland or muscle may show increased FDG uptake (Fig. 10) mimicking tumour recurrence and careful analysis of postoperative neck changes can help to solve this diagnostic dilemma. Post-surgical inflammatory oedema, scarring and granulation tissue can also cause increased FDG uptake making the interpretation of PET/CT studies very difficult in particular if the CT part of the PET/CT study comprises only a low dose CT for attenuation correction or if no CECT images are available (Fig. 10). Granulation tissue is the first step in wound healing and develops from connective tissue around the damaged area [52, 53]. It mainly contains inflammatory cells, fibroblasts, myofibroblasts and small vessels [52]. Over time, myofibroblasts and small vessels gradually disappear and granulation tissue evolves into immature and then mature scar. The mechanism responsible for this process is granulation tissue apoptosis, which mainly occurs between 20 and 25 days after injury, the fibroblastic apoptotic cells being continuously removed by macrophages [52]. Histological and morphometric studies have shown that the transformation of granulation tissue into scar tissue usually takes place within the first 2 months of injury [52], However, the duration of this process may vary depending on the amount of damaged tissue. As this transformation is a continuous process, there is a smooth transition between granulation tissue, early (immature) scar with limited amount of collagen and late (mature) scar with significant collagen deposition. Major FDG uptake, as seen on PET/CT images, is typically seen during the first weeks to months after surgery; it tends to decrease gradually over time. Post-surgical anatomical distortion can further increase the diagnostic dilemma in such cases. Therefore, it is generally recommended that the follow up PET/CT be performed at least 4–6 weeks after surgery after acute inflammation has subsided. Detailed knowledge of the previous surgical procedure and surgical complications (abscess, phlegmon, flap necrosis) helps to avoid diagnostic errors. Occasionally, to make the PET/CT image fusion precise, an additional MRI may be necessary to avoid misdiagnosis [1–4, 8, 42] (Fig. 10).Fig. 9

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