Incidental thyroid carcinoma identified by positron emission tomography scanning obtained for metastatic evaluation

Positron emission tomography (PET) scanning is an emerging technology with substantial implications for patients with solid tumors. PET is useful in i dentifying sites of metastatic disease as well as primary malignancy and ev aluating suspicious findings found via other imaging modalities. PET is bec oming a standard modality for metastatic evaluation of a variety of maligna ncies. However, this imaging is not limited by histology and may reveal cli nically occult second lesions. We present five cases of a clinically occult thyroid cancer found in patients who underwent PET scanning for metastatic evaluations. The principal diagnoses included two patients with malignant melanoma, one each with gastric, rectal, and colonic adenocarcinoma. None o f the cases had findings on physical examination. Increased uptake in the r egion of the thyroid was evident on the PET scan, and fine-needle aspiratio n biopsy indicated papillary carcinoma of the thyroid in all five cases. Al though evaluation of metastatic disease is the primary purpose for PET in t his setting the discovery of occult thyroid malignancy is an additional ben efit of such imaging. This emphasizes the importance of investigating suspi cious areas found by PET and not simply assuming that these are all sites o f metastatic disease. Furthermore incidental findings of uptake in the regi on of the thyroid make consideration of a primary carcinoma mandatory.