F-18-FDG for detecting occult primary tumors in patients with lymph node metastases in the neck.

Background: The occult primary tumor remains an important diagnostic problem in patients with lymph node metastases despite a large variety of imaging modalities. Therefore, the aim of our study was to evaluate the impact of F-18-FDG-positron-emission-tomography (PET) in these patients. Methods: The study group included a total of 28 patients aged 39 to 84 years with cervical lymph node metastases of a histologically confirmed squamous cell carcinoma (n = 24) or an undifferentiated carcinoma (n = 4). All patients received 370 MBq F-18-FDG intravenously, and whole-body images were acquired at 60 min p. i. with an ECAT EXACT 47 (921) (Siemens, CTI). All lesions were evaluated either by histology or by CT/MRI. Results: In 12 patients PET did not reveal suspected tumorous lesions. In contrast in 16/28 patients PET showed focal tracer accumulations corresponding to potential primary tumor sites located in the lungs (n = 7), in the region of the tonsilla palatina (n = 5), in the submandibular gland (n = 1), in the nasopharynx (n = 1), in the larynx (n = 1), or at the base of the tongue (n = 1). In nine out of these 16 patients, the primary was confirmed in the lungs in 5 patients, in the larynx, at the base of the tongue, in the nasopharynx, and the tonsilla palatina in one patient each, respectively. Moreover, in 6 out of 16 patients, PET was false-positive. One patient refused further evaluation of PET findings. Conclusions: In approximately one third of all patients, PET detected the primary tumor site, which significantly influenced further therapeutic procedures. Thus, F-18-FDG-PET may be a valuable diagnostic tool in the detection of the primary tumor in patients with cervical lymph node metastases.