The role of positron emission tomography in occult primary head and neck cancers

PURPOSE To evaluate the utility of positron emission tomography (PET) fluorodeoxygl ucose (FDG) imaging in the workup of unknown primary head and neck tumors. METHODS Fourteen patients with squamous cell carcinoma of cervical lymph node metas tasis of unknown primary origin (clinical stage N2-N3) were studied prospec tively. The patients underwent conventional workup, including physical exam ination, computed tomography, and random biopsies of the potentially suspec ted sites. If no primary site was found, 8 to 13 mCi of FDG was given intra venously, and whole-body scans with standardized uptake values were obtaine d. The results of FDG-PET imaging were compared with clinical, CT, and hist opathologic 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 conf irmed, AU these primary sites were not visualized on CT or physical examina tion, 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 identi fy a primary tumor, but a nasopharyngeal carcinoma was identified in post-r adiation therapy follow-up PET. In the remaining nine patients, a primary l esion was never found. All cervical lymph nodes detected by CT were identif ied 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 guidi ng endoscopic biopsies for histologic diagnosis and treatment options.