[The role and limitations of FDG-PET in head and neck cancer]

18F-fluorodeoxyglucose positron emission tomography (FDG-PET) is a nuclear medicine imaging technique which has been increasingly applied as a diagnostic tool. The usefulness of FDG-PET may be described as follows: I . Early detection of cancer; II. Diagnosis of cancer; III. Detection of nodal or distant metastasis, and double cancer; IV. Detection of unknown primary tumor with metastatic neck lesions; and V. Evaluation of treatment of head and neck cancer. FDG-PET is especially useful to detect distant metastasis, double cancer with head and neck cancer and unknown primary tumor with metastatic neck lymph nodes. The conventional modalities, e. g., CT or MRI, show anatomical images in the body. On the other hand, FDG-PET reveals three-dimensional images of functional processes of the glucose metabolism. FDG-PET can estimate metabolic activity in cancer and is useful in evaluating or monitoring the response to concurrent chemoradiotherapy of the head and neck cancer. However, we should recognize the limitations of FDG -PET. An acute inflammatory disease shows high FDG uptake like cancer. It is difficult to detect early-stage esophageal cancer or to diagnose parotid gland cancer.