T Tg level

131I WBS(-)

Acc, accuracy; PPV, positive predictive value; NPV, negative predictive value; WBS, whole-body scan.

Acc, accuracy; PPV, positive predictive value; NPV, negative predictive value; WBS, whole-body scan.

therapy. High-dose 131I therapy does not appear to have a tremendously beneficial effect on the viability of metastatic FDG-avid lesions. Nonresectable regional disease can be treated with external-beam irradiation or, if limited, with surgery, while widespread disease may be amenable to experimental chemotherapy.

Hürthle Cell Carcinoma

Hürthle cell cancer is a histologic subtype of DTC that is clinically more aggressive and has little or no iodine uptake. In a study of 12 patients Lowe et al.66 described a sensitivity of 92% for FDG-PET. Plotkin et al.67 reported a sensitivity of 92%, a specificity of 80%, a PPV of 92%, a NPV of 80%, and an accuracy of 89% (Table 33.3).

Medullary Thyroid Cancer

Medullary thyroid cancer (MTC) is a rare calcitonin-secreting tumor originating from the parafollicular C cells. At the time of initial diagnosis, most of the patients with this malignancy are noted to have lymph node metastases. The primary treatment modality is surgical resection of all malignant lesions. Brandt-Mainz et al.68 studied 20 patients and found the overall sensitivity to be 76%. In another study, Diehl et al.69 demonstrated, in 55 cases, that FDG-PET had a sensitivity of 78% and a specificity of 79%, in comparison with 131In-pentetreotide, 25% and 92%, with dimercaptosuccinic acid (DMSA), 33% and 78%, with 99mTc-MIBI (hexakis-2-methoxy-2-isobutyl isonitrile), 25% and 100%, with CT, 50% and 20%, and with MRI, 82% and 67%. A reasonable imaging approach in the staging and follow-up of MTC would be a combination of FDG-PET and MRI.

Novel, more-specific PET tracers, such as 18F-dihydroxy-phenylalanine and 6-18F-DOPAv (dopamine), have been proposed by Hoegerle et al.70 and Courgiotis et al.,71 respectively, with promising results, especially in lymph node staging. Nonetheless, FDG-PET has assumed an increasingly important role in the management of thyroid cancer. The ability of this method to detect many non-iodine-avid tumor foci is of considerable practical utility and is changing the practice of thyroidology. Our own experience suggests that, in patients with thyroid cancer with possible recurrence of non-iodine-avid disease, FDG-PET/CT (ideally under TSH stimulation) is an excellent method to precisely locate recurrent tumors and to direct the surgeon to their precise location if surgical intervention is being considered.

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