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Year:
2012
| Volume: 20
| Issue: 3-4
| Pages: 112-116
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Special Article |
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PET/CT IN THYROID CARCINOMA
Jasna Mihailovic |
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DOI:
10.2298/AOO1204112M |
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Abstract: |
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The diagnostic imaging procedures that have a role in detection of malignant thyroid tissue are radioiodine (131I) diagnostic whole-body scintigraphy (WBS), neck ultrasound, and CT and MRI for evaluation of the mediastinal area. Despite excellent morphologic characterization of metastatic nodal recurrences, MRI cannot reliably make a differentiation between benign and malignant lymph nodes. Although it detects enlarged metastatic lymph nodes, there are also many small nodal metastases that are usually missed. In one-third of patients with well differentiated thyroid carcinoma, there are carcinomas with dedifferentiated tumor cells: metastatic tissue may not concentrate radioiodine well; thus 131I-WBS is negative despite elevated thyroglobulin (Tg) levels. Although MRI helps in detection of these non-iodine avid metastases, FDG PET/CT can perform more effectively. Due to its high glycolytic rate, changes in glucose transport systems and hexokinase activity, [18F] fluorodeoxyglucose (FDG) accumulates in malignant tissue and is useful for identification of distant metastases in these patients. Iodine positive metastases are often negative with FDG-PET imaging while iodine negative metastases exhibit increased FDG-uptake. If a metastatic lesion is identified by FDG positron emission tomography/computed tomography (PET/CT), the usual approach is to first send the patient to surgery for removal of neoplastic tissue, if possible. This is followed by re-treatment with 131I therapy after tumor redifferentiation with retinoic acid. In a limited number of patients, iodine negative thyroid cancer may express somatostatin receptors and radiopeptide therapy may be utilized. FDG PET/CT is a hybrid imaging diagnostic tool which helps in detection of non-iodine avid metastases. It has a role in exact localization of recurrences which will assist in the decision to remove the malignant tissue surgically. |
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Key words:
Positron-Emission Tomography and Computed Tomography; Fluorodeoxyglucose F18; Thyroid Neoplasms; Diagnostic Imaging; Neoplasm Metastasis |
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