PET-CT/MR imaging in head and neck cancer: Physiologic variations, pitfalls, and directed applications

Abstract

The strengths and potential pitfalls of functional FDG-positron emission tomographic imaging in patients with head and neck cancer, especially in those who have undergone surgery and/or chemoradiation therapy, will be covered and carefully reviewed. Positron emission tomography (PET) is currently performed using the radiopharmaceutical 18F-FDG, a d-glucose analog. The increased vascularity of tumors and glucose metabolism by neoplastic cells result in preferential uptake of FDG by these cells. The inability to process the metabolites of this modified glucose molecule causes intracellular accumulation of F18-containing radioisotopes in tumors. This has been invaluable in the evaluation of many cancer patients, and PET now plays a pivotal role in the diagnosis, staging, and re-staging of head and neck oncology patients. The ability to assess the functional status of tissue with FDG-PET has been remarkable, and addresses this well-known limitation of conventional cross-sectional computed tomography (CT) and magnetic resonance (MR) imaging. Conversely, the excellent spacial resolution and the ability to analyze the relationship of neoplasms relative to critical adjacent anatomic structures on CT and MR imaging are a very important adjuvant to, and limitation of, PET. This chapter will emphasize pertinent head and neck anatomy, and common physiologic variations in PET imaging, with particular attention to those seen in the treated neck, and will illustrate the complimentary roles that PET and cross-sectional imaging play in assessing patients with newly diagnosed and treated head and neck cancers. The precise roles that functional and anatomic imaging will play in monitoring therapy, surveillance imaging, and their potential impact on patient outcomes continue to evolve.