Investigation of thyroid, head, and neck cancers with PET Hongming Zhuang, MD, PhD a , Rakesh Kumar, MD a , Susan Mandel, MD b , Abass Alavi, MD a, * a Division of Nuclear Medicine, Department of Radiology, Hospital of the University of Pennsylvania, 3400 Spruce Street, 110 Donner Building, Philadelphia, PA 19104, USA b Department of Internal Medicine, Hospital of the University of Pennsylvania, Philadelphia, PA 19104, USA PET with [ 18 F]-fluorodeoxyglucose (FDG) has been accepted as a useful imaging modality for the diagnosis of a variety of malignancies. This article discusses the use of FDG-PET in the management of patients with thyroid and head or neck cancers. Thyroid cancer Diagnosis and staging of papillary and follicular thyroid cancer Initial reports suggested that FDG-PET may prove useful in characterizing thyroid nodules assuming that malignant lesions have more FDG uptake than benign nodules [1,2]. It was reported that FDG-PET could detect lymph node metastasis prior to thyroid- ectomy patients with cancer [3]. Based on the experience gained over the past decade, however, the role of FDG-PET in the diagnosis and initial staging of thyroid cancers seems to be limited. First, thyroid tumors, which are well differentiated and retain the ability to synthesize hormones from iodine, have low glucose metabolism. Tumors without this functional differentiation for iodine (I-123 or I-131) uptake show high glucose metabolism [4]. Many differentiated papillary and follicular thyroid cancers do not have increased FDG accumulation. In addi- tion, many nonmalignant thyroid disorders, such as multinodular goiter [3,5,6] or thyroiditis [7,8], may have increased FDG uptake. FDG-PET is unlikely to differentiate successfully benign and malignant tumors [9]. Furthermore, it is now known that in- creased thyroid-stimulating hormone (TSH) levels stimulate FDG uptake by thyroid cancer cells [10,11]. The patients without thyroidectomy often have relatively low TSH levels and FDG uptake by the thyroid cancer is relatively low. Nevertheless, FDG- PET might be of value in the detection of unexpected thyroid cancer when PET is used in the assessment of other pathologies. From a retrospectively study in- volving 1330 subjects who mainly underwent FDG- PET for cancer evaluation, Kang et al [12] reported that the thyroid incidentaloma was found in 2.2% of the patients. Among those thyroid incidentalomas, 26.7% proved to be thyroid cancer. In a similar study involving 4525 patients, Cohen et al [13] reported that the prevalence of thyroid incidentaloma was 2.3% and 47% of these incidentaloma were thyroid cancer. The ability of FDG-PET in the early detec- tion of thyroid cancer should not be overlooked. Recurrent or metastatic papillary and follicular thyroid cancers Papillary and follicular thyroid cancers are among the most curable of all malignancies. Some patients, however, are at high risk for recurrence and metas- tasis or even death from their cancers. I-131 whole- body scintigraphy and determination of thyroglobulin levels are well-established methods for the assess- ment of tumor recurrence and metastasis in patients with thyroid cancer. Recently, I-123 whole-body scan has been proposed to have better accuracy in this clinical setting [14]. In some patients, however, 0033-8389/04/$ – see front matter D 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.rcl.2004.07.006 * Corresponding author. E-mail address: alavi@oasis.rad.upenn.edu (A. Alavi). Radiol Clin N Am 42 (2004) 1101 – 1111