Purpose: To evaluate the utility of positron emission tomography (PET) fluorodeoxyglucose (FDG) imaging in the workup of unknown primary head and neck tumors.
Methods: Fourteen patients with squamous cell carcinoma of cervical lymph node metastasis of unknown primary origin (clinical stage N2-N3) were studied prospectively. The patients underwent conventional workup, including physical examination, computed tomography, and random biopsies of the potentially suspected sites. If no primary site was found, 8 to 13 mCi of FDG was given intravenously, and whole-body scans with standardized uptake values were obtained. The results of FDG-PET imaging were compared with clinical, CT, and histopathologic findings. To eliminate bias, PET scans were reviewed by nuclear medicine physicians who had no previous knowledge of the other findings.
Results: PET identified the location of primary tumor in three patients: lung hilum, base of tongue, and pyriform sinus. These lesions were pathologically confirmed. All these primary sites were not visualized on CT or physical examination, except for a pyriform sinus lesion, which was seen on CT, but initial biopsy result was negative. In one patient, the initial PET did not identify a primary tumor, but a nasopharyngeal carcinoma was identified in post-radiation therapy follow-up PET. In the remaining nine patients, a primary lesion was never found. All cervical lymph nodes detected by CT were identified by PET.
Discussion: A previously unknown primary tumor can be identified with FDG-PET in about 21% of the patients in our prospective series. PET can be of value in guiding endoscopic biopsies for histologic diagnosis and treatment options.