Search

Poorly differentiated insular thyroid carcinoma is now classified as a separate entity among other tumors of the thyroid gland. Its histologic pattern and its clinical course are regarded as intermediate between well differentiated and anaplastic thyroid cancer. Insular carcinoma accumulates I-131, but no data exist regarding its fluorodeoxyglucose (FDG) positron emission tomographic (PET) uptake. The authors report F-18 FDG PET, Tc-99m MIBI, and radioiodine imaging features in a 63-year-old patient with metastatic insular thyroid carcinoma. After total thyroidectomy (for poorly differentiated insular carcinoma pT3a), the patient was referred for radioiodine ablation. No signs of recurrence were present until 16 months later, when thyroglobulin levels increased. An I-131 scan showed a single lesion in the right lung, and further radioiodine treatment was administered (cumulative dose [530 mCi], 19,610 MBq I-131). Three years after the initial diagnosis, FDG-PET and Tc-99m MIBI scans were performed within 5 days during thyroxine treatment. After that, thyroxine substitution was withdrawn; 6 weeks later, an I-131 whole-body scan was performed. Both radioiodine and MIBI images showed increased tracer uptake in the known lung lesion. However, FDG PET showed a normal tracer distribution. Magnetic resonance and computed tomographic imaging confirmed a 12-mm lesion in the right upper lobe. These findings support the concept of the "flip-flop phenomenon" in insular thyroid carcinoma, an alternating pattern of metastases with either I-131 or FDG-uptake. Despite poorly differentiated histologic findings, glucose metabolism was not increased in this patient with an insular tumor.

Cutaneous recurrence after resection of gastric cancer is relatively rare. The authors describe a patient with cutaneous metastasis as the first sign of relapse 4 months after resection of a primary gastric cancer. F-18 fluorodeoxyglucose positron emission tomography (F-18 FDG PET) was performed after normal results were obtained with conventional staging and revealed a cutaneous metastasis on the patient's back and a second cutaneous lesion in the abdominal wall, which were verified by biopsy. In addition, the F-18 FDG-PET images disclosed abdominal lymph node involvement. This case illustrates the ability of F-18 FDG PET to detect metastatic tumor spread in unexpected sites as clinically inapparent cutaneous metastases in gastric cancer.