Imaging of neck metastases.

Awareness of the presence of cervical node metastasis is important in treatment planning and in prognostic prediction for patients with head and neck cancer. Currently, MRI and CT are commonly used to evaluate the primary tumor and the neck status. They characterize the cervical lymph nodes dependent on morphological criteria. However, metastases may be missed in some morphologically normal nodes. Conversely, it is difficult to discriminate reactive hyperplasia from metastasis in some enlarged nodes. Doppler ultrasound with fine-needle aspiration can overcome some of these limitations, but it is dependent on the sonographer's skill level and may be impractical in some cases due to too many questionable nodes. Positron emission tomography (PET) is a functional imaging that can detect metastasis lesions by pinpointing regions of high metabolism. It is better suited for assessing metastases to lymph nodes that appear morphologically normal. The main drawback of PET is its poor anatomical resolution. Side-by-side visual correlation of PET and CT/MRI can help determine the anatomical location of abnormal PET uptake and eliminate some false-positive PET findings caused by spatial errors. Fused PET/CT is considered to be the most accurate imaging modality for detecting nodal metastases, because it simultaneously provides prompt and accurate coregistration of functional and anatomical images. However, it is expensive, less-often available, and still constrained by technical resolution limits for tiny nodal metastases. Diffusion-weighted MRI, dynamic contrast-enhanced MRI, and nanoparticle-enhanced MRI are novel imaging technologies that have been exploited to enhance the detection of metastatic nodes. The initial results have been promising; however, micrometastases can still not be detected, and the extra costs and logistical burdens associated with these techniques prevent them from gaining wider acceptance. To date, neck dissection with detailed pathological examination is the gold standard. There is always a need for further refinement of the imaging techniques that can provide accurate information that approaches this gold standard.