Role of 18F-FDG PET/CT in pre and post treatment evaluation in head and neck carcinoma

Figure 5 Positron emission tomography/computed tomography underestimates size and extension of the nasopharyngeal carcinoma and retropharyngeal lymph nodes compared to magnetic resonance imaging. The approximate lateral extension (red arrows) of the nasopharyngeal carcinoma is well demarcated on magnetic resonance imaging (MRI) (A). The tumor appears to be smaller on positron emission tomography/computed tomography (CT) (B) as compared to MRI because the lateral portion of the tumor is hypometabolic. Inferior to the primary tumor site, there is metastatic bilateral retropharyngeal lymphadenopathy (yellow and green arrows). The full extent of retropharyngeal lymph node involvement is better assessed by MRI (C) than CT (D). Only the right lateral retropharyngeal node is FDG avid.