Lymph node staging with dual-modality PET/CT: Enhancing the diagnostic accuracy in oncology
Introduction
The TNM classification is the worldwide accepted and used system for categorizing and staging of all solid tumors. The T-stage indicates the tumor size, whereas the N-stage shows the extent of metastatic spread to lymph nodes. The M-stage accounts for solid metastases in distant organs.
Radiological imaging procedures are an essential step in cancer diagnosis as they provide the referring physician with information about the patients’ tumor status. Imaging procedures for tumor staging are based on morphological and functional data. However, morphological imaging like MRI, CT, and ultrasound are based on strictly anatomical information such as lymph node size, shape, and the pattern of contrast enhancement, and are known to be of only of limited sensitivity and specificity when staging lymph nodes for metastatic spread. Positron emission tomography (PET) using [18F]-2-fluoro-2-desoxy-d-glucose (FDG) as a radioactive tracer has proven superior to morphologic imaging procedures when assessing the N-stage based on functional data evaluating tumor metabolism [1]. Tumor cells metabolise more glucose compared to normal adjacent tissue, leading to increased uptake of the glucose analogue FDG in the majority of solid tumors. However, the major downside of functional imaging alone is the limited morphological information which can render the exact anatomical localisation of an area of increased glucose metabolism difficult. Therefore, the combination of morphological and functional imaging represents the optimal approach for lymph node staging and general staging. Several attempts have been made to fuse both imaging modalities, but apart from accurate fusion of brain data sets, image co-registration in other parts of the body has remained unsatisfactorily so far for clinical routine, based on the time required as well as limitations associated with respiratory motion and organ movement. Dual-modality PET/CT scanners have demonstrated to overcome these limitations. In this hybrid imaging tool, the CT and the PET are acquired in direct succession with the patient scanned in the same position during CT and PET for accurate image fusion. Thus, limitations of image fusion associated with different patient positions are minimized. Several studies evaluating patients with different oncological diseases have reported outstanding results concerning the TNM staging when using PET/CT instead of separate morphological and functional data sets [2], [3], [4], [5]. Therefore, dual-modality FDG–PET/CT is expected to play an important role in lymph node diagnostics as it will enhance the tumor staging accuracy which is essential for tailored oncological therapy. This article summarized advantages and limitations of PET/CT imaging in lymph node staging.
Section snippets
Technical considerations
The underlying principle of currently available PET/CT systems is the acquisition of two dedicated imaging procedures, CT and PET, in a single step followed by image co-registration. Both modalities are physically aligned in one setting which is served by a single examination table (Fig. 1). The CT is acquired first followed by the PET. Since the patient is scanned with CT and PET while in the same position on the examination table, both data sets can be accurately co-registered. Depending on
PET/CT and morphological imaging procedures
The appearance of non suspicious lymph nodes with morphological imaging procedures is classified by their shape, size, density and, if applied, contrast enhancement. Benign nodes usually tend to have a fatty hilum, an oval shape and frequently do not measure more than 1 cm in the short axis diameter. Size-based measurements are the main criteria for differentiating benign from malignant lymph nodes. Physiologic lymph node size may vary based on their anatomical localisation [10], [11].
Thus,
PET/CT and positron emission tomography
PET imaging using FDG as a radioactive tracer has been reported a very sensitive and specific tool for the detection of lymph node metastases. In comparison with morphological imaging procedures higher sensitivities and specificities are based on the functional data provided by PET which offer visualization of tumor metabolism.
In the head and neck, PET was found to be 87% sensitive and 94% specific for staging of lymph nodes [14]. These results are well comparable with the published literature
Limitations of PET/CT
Most malignant tumors are associated with an increase in glucose metabolism leading to increased FDG-uptake on FDG–PET. However, there are tumors which are found to be frequently FDG–PET negative based on normal or even decreased glucose metabolism (Table 1). For these tumor entities implementation of alternative radioactive tracers into the clinical routine may improve the staging results with PET and PET/CT. For neuroendocrine tumors DOTATOC, a somatostatine analog, labelled with a
Conclusion
Accurate tumor staging is essential for patients’ therapy planning. Compared with morphological imaging procedures PET/CT provides additional functional data which increase the diagnostic accuracy over morphology alone when staging lymph nodes for malignant spread. Furthermore, morphological data in accurate fusion with functional images from PET have further improved the accuracy when detecting malignant lymph nodes with PET/CT compared to PET alone. Compared to both, morphology and function
Acknowledgements
The authors would like to thank Sandra Pabst, RT, Janina Marchese, RT and Bearbel Terschüren, RT as well as Slavco Maric and Stergios Gradas, RT for the acquisition and preparation of the PET/CT images.
References (30)
- et al.
Positron emission imaging of head and neck cancer, including thyroid carcinoma
Semin Nucl Med
(2004) Colorectal cancer. Radiologic staging
Radiol Clin North Am
(1997)- et al.
FDG–PET in the locoregional lymph node staging of non-small cell lung cancer. A comprehensive review of the leuven lung cancer group experience
Clin Positron Imaging
(1999) - et al.
A tabulated summary of the FDG PET literature
J Nucl Med
(2001) - et al.
Non-small cell lung cancer: dual-modality PET/CT in preoperative staging
Radiology
(2003) - et al.
Whole-body dual-modality PET/CT and whole-body MRI for tumor staging in oncology
JAMA
(2003) - et al.
Clinical performance of PET/CT in evaluation of cancer: additional value for diagnostic imaging and patient management
J Nucl Med
(2003) - et al.
Direct comparison of (18)F-FDG PET and PET/CT in patients with colorectal carcinoma
J Nucl Med
(2003) - et al.
A combined PET/CT scanner for clinical oncology
J Nucl Med
(2000) - et al.
Dual-modality PET/CT imaging: the effect of respiratory motion on combined image quality in clinical oncology
Eur J Nucl Med Mol Imaging
(2003)
Whole-body positron emission tomography-CT: optimized CT using oral and IV contrast materials
AJR Am J Roentgenol
To enhance or not to enhance? 18F-FDG and CT contrast agents in dual-modality 18F-FDG PET/CT
J Nucl Med
Normal mediastinal lymph nodes: number and size according to American Thoracic Society mapping
AJR Am J Roentgenol
Computed tomography of cervical and retropharyngeal lymph nodes: normal anatomy, variants of normal, and applications in staging head and neck cancer. Part I: normal anatomy
Radiology
Metastases from non-small cell lung cancer: mediastinal staging in the 1990s—meta-analytic comparison of PET and CT
Radiology
Cited by (46)
Insights about cervical lymph nodes: Evaluating deep learning–based reconstruction for head and neck computed tomography scan
2023, European Journal of Radiology OpenPrimary Adrenal Malignancy
2022, Oncologic Imaging: A Multidisciplinary ApproachPrimary Adrenal Malignancy Anatomy of adrenal cortical carcinoma.
2012, Oncologic Imaging: A Multidisciplinary Approach Expert ConsultPrimary adrenal malignancy
2012, Oncologic Imaging: A Multidisciplinary ApproachPostoperative FDG-PET/CT staging in GIST: Is there a benefit following R0 resection?
2011, European Journal of RadiologyCitation Excerpt :Based on the results of this study, the sensitivity of postoperatively performed FDG-PET/CT for the detection of unknown metastases seems to be low. As opposed to other tumor entities [22,23] FDG-PET/CT does not seem to be a sufficient tool to detect yet unknown metastases in GIST patients in a postoperative setting. Close follow-up examinations must be considered a more adequate approach to postoperative management in the R0/M0 setting.
Lymph Node Imaging in Gynecologic Malignancy
2010, Seminars in Ultrasound, CT and MRICitation Excerpt :For example, macrophages in inflammatory and infectious lesions demonstrate FDG uptake.81 False-negative results may occur in situations in which lymph nodes are small (the spatial resolution of most PET-CT systems is 4-5 mm), the node is near to the primary tumor, for micrometastases,82,83 or if there is extensive nodal necrosis with little residual metabolically active tissue84 (Fig. 9C). Currently, FDG-PET/CT is advocated to help stage advanced cervical cancer and in planning radiotherapy fields.