J Nucl Med 1999 Jun;40(6):986-92
Value of FDG PET in papillary thyroid carcinoma with negative 131I whole-body
scan.
Chung JK, So Y, Lee JS, Choi CW, Lim SM, Lee DS, Hong SW, Youn YK, Lee MC, Cho
BY.
The management of metastatic thyroid carcinoma patients with a negative 131I
scan presents considerable problems. Fifty-four athyrotic papillary thyroid
carcinoma patients whose 1311 whole-body scans were negative underwent
18F-fluorodeoxyglucose (FDG) PET; the purpose was to determine whether this
procedure could localize metastatic sites. We also assessed its usefulness in
the management of these patients. METHODS: Whole-body emission scan was
performed 60 min after the injection of 370-555 MBq 18F-FDG, and additional
regional attenuation-corrected scans were obtained. Metastasis was
pathologically confirmed in 12 patients and was confirmed in other patients by
overall clinical evaluation of the findings of other imaging studies and of the
subsequent clinical course. RESULTS: In 33 patients, tumor had metastasized,
whereas 21 patients were in remission. FDG PET revealed metastases in 31
patients (sensitivity 93.9%), whereas thyroglobulin levels were elevated in 18
patients (sensitivity 54.5%). FDG PET was positive in 14 of 15 metastatic cancer
patients with normal thyroglobulin levels. In 20 of 21 patients in remission,
FDG PET was negative (specificity 95.2%), whereas thyroglobulin levels were
normal in 16 patients (specificity 76.1%). The sensitivity and specificity of
FDG PET were significantly higher than those of serum thyroglobulin. In patients
with negative 1311 scans, FDG PET detected cervical lymph node metastasis in
87.9%, lung metastasis in 27.3%, mediastinal metastasis in 33.3% and bone
metastasis in 9.1%. In contrast, among 117 patients with 131I scan-positive
functional metastases, 131I scan detected cervical lymph node metastasis in
61.5%, lung metastasis in 56.4%, mediastinal metastasis in 22.2% and bone
metastasis in 16.2%. In all 5 patients in whom thyroglobulin was false-negative
with negative antithyroglobulin antibody, PET showed increased 18F-FDG uptake in
cervical lymph nodes, mediastinal lymph nodes, or both. Among patients with
increased 18F-FDG uptake only in the cervical lymph nodes, the nodes were
dissected in 11. Metastasis was confirmed in all, even in normal-sized lymph
nodes. CONCLUSION: FDG PET scan localized metastatic sites in 131I scan-negative
thyroid carcinoma patients with high accuracy. In particular, it was superior to
131I whole-body scan and serum thyroglobulin measurement for detecting
metastases to cervical lymph nodes. FDG PET was helpful for determining the
surgical management of these patients.
