Value of fused positron emission tomography CT in detecting primaries in patients with primary unknown cervical lymph node metastasis

Objective: Identification of the primary tumour can prolong the life expectancy of patients with primary unknown cervical lymph node metastasis (PUCLNM) through targeted therapy. This study investigated the value of 18F-fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET-CT) at identifying primaries in patients with PUCLNM. Methods: Twenty-seven patients (21 males and 6 females, median age 48.2 +/- 16.3, age range 30-73) with PUCLNM underwent FDG PET-CT to search for the primary tumour, which could not be detected by conventional diagnostic modalities. The results were analysed and correlated with either pathological findings or clinical follow up. Results: Pathological FDG uptake suspicious for the primary was detected in 13 cases, while the primary tumour remained occult in 14 cases. Eleven of 13 patients with suspected primaries were confirmed by histological findings. One with a coexisting second tumour and three with unexpected distant metastases were found in patients with confirmed primaries. The most common primary location in patients with PUCLNM found in our study was nasopharynx. In those 14 patients with negative FDG PET-CT results, only one patient had a primary malignancy that was proven histologically after endoscopy with biopsy during a period of clinical follow up. The sensitivity, specificity, accuracy and positive predictive values of FDG PET-CT were 91.7, 86.7, 88.9 and 84.6%, respectively. Conclusion: FDG PET-CT is a useful tool to help search for unknown primaries in patients with cervical lymph node metastasis and has an acceptable diagnostic yield for the detection of distant malignancies.