The impact of FDG PET on the management of occult primary head and neck tumours.

AIMS: The aim of this study was to investigate the impact of positron-emission tomography (PET) with 18F-labelled fluoro-2-deoxy-D-glucose (FDG) in the management of occult primary head and neck tumours.

MATERIALS AND METHODS: We reviewed 16 patients with squamous cell carcinoma (SCC) and one patient with undifferentiated carcinoma of cervical lymph nodes (N1-4; N2a-9; N2b-2; N3-2). All patients had full clinical assessment, including examination under anaesthesia (EUA), with biopsy of all suspicious areas and random biopsies of sites likely to harbour an occult primary site. Nine patients underwent magnetic resonance imaging (MRI) of the head and neck, three underwent computed tomography (CT) and five underwent both CT and MRI. None of these studies were able to locate a primary tumour. Patients received 350 MBq FDG intravenously. Emission transmission scans of the extra-cranial head, neck and thorax were obtained using an ECAT Exact 47 at least 60 min after injection. The images were interpreted by the same radiologist experienced in PET, independent of the final outcome. The influence of FDG PET on management was assessed on review of the patients' notes after treatment or when treatment had been deemed unnecessary.

RESULTS: FDG PET suggested a primary site in eight of the 17 patients (tongue base 5; nasopharynx 1; tonsil 1: supraglottis 1). Pathological confirmation was obtained in four patients and one patient died of progressive disease at the primary site. In nine patients, the primary site was not identified on FDG PET. In six of these patients, no primary site was found during follow-up (range 8-36 months: mean 20 months). One patient died before treatment commenced, and there were two histologically confirmed false-negative FDG PET results: one tonsil SCC and one lateral pharyngeal wall SCC. FDG PET affected treatment plans in nine of the 17 (53%) patients in whom a primary site was suggested (altered radiotherapy plan 6; radiotherapy with curative intent to palliative radiotherapy 1; radiotherapy to surgery and post-operative radiotherapy 1), and in one patient where no occult primary was localised (radiotherapy to surgery 1). FDG PET had a sensitivity, specificity, positive and negative predictive value of 62%, 66%, 62% and 62%, respectively.