Post-treatment surveillance of head and neck cancer: pitfalls in the interpretation of FDG PET-CT/MRI.

QUESTIONS UNDER STUDY We investigated non-malignancy-associated (¹⁸F)fluoro-deoxy-D-glucose (FDG) uptake in the head and neck cancer (HNC) post-treatment follow-up with positron emission tomography - computed tomography / magnetic resonance imaging (PET-CT/MRI). A retrospective study on HNC patients undergoing follow-up or re-staging PET-CT/MRI examinations was performed. Thereby, FDG-positive regions were morphologically correlated to the CT and MRI images and a statement regarding tumour persistence/recurrence. METHODS FDG-positive lesions were assessed according to their anatomical localisation and categorised as true positive, true negative, false positive or false negative findings. The gold standard for verification of an FDG-positive lesion was the cytological or histopathological examination of the region of interest. The most likely aetiology was assessed according to the following categories: (1.) physiological uptake (2.) post-surgical, inflammatory uptake, (3.) post-irradiation, inflammatory uptake and (4.) reactive, not otherwise specified. RESULTS Tumour recurrence / tumour persistence was found in 14/87 patients (16.1%). A total of 159 non-malignancy-associated FDG-positive lesions were found. Every PET-CT/MRI examination revealed 2.1 ± 1.5 FDG-positive lesions in the head and neck. A total of 107 FDG-positive lesions (67.3%) were categorised as physiological, 52 FDG-positive lesions (32.7%) as inflammatory (post-surgical: n = 14, 8.8%; post-irradiation: n = 9, 5.7%; reactive, not otherwise specified: n = 29, 18.2%). Eight patients (11.8%) underwent invasive diagnostic procedures to clarify indistinct findings. CONCLUSIONS Post-treatment follow-up of HNC patients requires interdisciplinary management and familiarity with the patient's past medical history. Awareness of common confounders of FDG positivity often allows clarification of indistinct lesions. However, a substantial number of approximately 12% of FDG-positive lesions remain unclear unless invasive diagnostic procedures are performed.