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Objective: Numerous authors have reported the potential usefulness of positron emission tomography (PET). These studies have had conflicting results, at least partly owing to limited sample sizes. The objective of this study is to define not only the uses, but also the limitations of PET in patients with head and neck cancer.Study Design: Nonrandomized, retrospective analysis of PET at an academic institution.Methods: The authors performed 146 PET scans on 133 patients with head and neck cancer. Eighteen patients (19 PET scans) with thyroid disorders were excluded. A minimum 1 year of follow-up was available in 84 patients, who were separated into groups based on whether the PET was used to detect unknown primary cancers (n = 20), stage neck nodal and distant metastases (n = 8), monitor response to nonsurgical therapy (n = 22), or detect recurrent or residual cancers (n = 34). The results of PET were compared with results from computed tomography (CT) and magnetic resonance imaging (MRI) performed in the same patients.Results: Of the unknown primary cancers, PET correctly identified 7 of 20 primary sites, giving a sensitivity of 35%. When combined with CT or MRI, the sensitivity increased to 40%. When used for detection of metastatic disease, PET demonstrated five of five nodal metastases (100%) and two of four distant metastases (50%). In evaluating the response to nonsurgical therapy, PET had a sensitivity of 50% and a specificity of 83% for detecting tumor at the primary site and a sensitivity of 86% and a specificity of 73% for detecting nodal disease. When used for evaluation of recurrent/residual disease, PET identified seven of seven cases of local recurrences/residual disease and had a specificity of 85%. PET also detected seven of seven cases of nodal disease and had a specificity of 89%.Conclusions: For staging purposes, PET is limited by its lack of anatomic detail. However, PET compares favorably with CT and MRI in detecting recurrent/residual cancers. PET imaging complements the more traditional imaging modalities (CT or MRI), especially for an unknown primary cancer. [ABSTRACT FROM AUTHOR]