The role of fluorodeoxyglucose positron emission tomography in cervical lymph node metastases from an unknown primary tumor.

Background: The authors performed a comprehensive review of the efficacy of fluorodeoxyglucose positron emission tomography (FDG-PET) in the detection of primary tumors in patients with cervical metastases from unknown primary tumors.

Methods: Sixteen studies (involving a total of 302 patients) published between 1994 and 2003 were reviewed. These studies evaluated the role of FDG-PET in the detection of unknown primary tumors after conventional workup. In all studies, conventional workup included either panendoscopy or computed tomographic/magnetic resonance imaging, and in 10 of 16 studies, both of these diagnostic techniques were performed before diagnosis.

Results: The overall sensitivity, specificity, and accuracy rates of FDG-PET in detecting unknown primary tumors were 88.3%, 74.9%, and 78.8%, respectively. Furthermore, FDG-PET detected 24.5% of tumors that were not apparent after conventional workup. FDG-PET imaging also led to the detection of previously unrecognized metastases in 27.1% of patients (regional, 15.9%; distant, 11.2%). FDG-PET had notably low specificity and a high false-positive rate (39.3%) in the tonsils. In contrast, the false-positive rates for FDG-PET of the base of tongue and hypopharynx were only 21.4% and 8.3%, respectively. FDG-PET exhibited decreased sensitivity to tumors in the base of tongue (81.5%). The sensitivity of this technique at other sites was 90.5%.

Conclusions: FDG-PET detected primary tumors that went undetected by other modalities in approximately 25% of cases and was sensitive in the detection of previously unrecognized regional or distant metastases in 27% of cases. FDG-PET had low specificity for tonsillar tumors and low sensitivity for base-of-tongue malignancies.