ABSTRACT
Background Head and neck cancers constitute approximately 5% of all malignancies. Most head and neck cancers are squamous cell carcinomas (HNSCCs) of paranasal sinuses, the areodigestive tract (nasopahrynx, oral cavity and oropharynx, hypopharynx), and larynx.1 Currently, the management of these cancers demands a multidisciplinary approach for therapy, including surgery, radiotherapy, and chemotherapy. The role of imaging in HNSCC is somewhat different from that applied in other malignancies. Many tumors (in particular of the naso-, oro-, and hypopharynx) present late, with bulky disease, invasion of the contiguous structures, and enlarged lymph nodes. The clinical diagnosis is often obvious, with direct access for biopsy. Therefore, imaging usually has a minor role in the initial diagnosis of the primary tumor, but it is essential for the success of treatment, which is based on accurate staging. Staging aims to evaluate the local extent of the tumor and to detect regional lymph node involvement, distant metastases, and synchronous/metachronous primary lesions. After primary therapy, imaging plays a major role in assessment of the response to treatment and early detection of cancer relapse.2-4
The normal anatomy of the head and neck is complex, and structures traverse many different planes and angles; therefore, cross-sectional imaging is required to study HNSCC. Currently, the most widely accepted crosssectional imaging modality is computed tomography (CT), and in some institutions magnetic resonance imaging (MRI). During recent years, positron emission tomography (PET) has been proposed as an additional cross-sectional technique to evaluate patients with HNSCC.5-9 CT and MRI detect and characterize tumors by studying their changes in morphology, electronic density (CT), or proton environment and density (MRI). PET studies the metabolic differences between tumors and normal tissues. Metabolism in tumors is different from that in normal tissues in several ways. Some of these differences can be visualized with PET, taking advantage of the peculiar physical and chemical properties of particular radiolabeled compounds
called PET radiopharmaceuticals. After intravenous injection into the patient, these radiopharmaceuticals are incorporated into metabolic pathways, and the signals emitted by the cells, which have actively accumulated them, can be registered by dedicated instruments (the PET scanners), which produce multiplanar tomographic images of the radiopharmaceutical distribution. Cancer cells usually have a higher metabolic activity than do normal cells, and thus, in PET imaging, cancer is depicted as a focal area of increased accumulation of the radiopharmaceutical (Figure 4.1).
