Advantages of US over other imaging techniques are its price and low patient burden. Furthermore, US is the only available imaging technique that can be used for frequent routine follow-up. Of the estimated 800 lymph nodes in the human body, 300 lymph nodes Ferroptosis activation are situated in the neck [2]. Presently, most clinicians use the classification into six levels as adapted by the American Academy of Otolaryngology or the 1991 American Academy of Otolaryngology Head and Neck Surgery (AAO-HNS) guidelines [3], because the majority of patients with head and neck malignancies presently

undergo sectional imaging prior to treatment planning. The transverse diameter of lymph nodes varies according to the different region. In the level 2 (superior internal jugular nodes), the minimal axial diameter is found out to be 7–8 mm in reactive lymph nodes and in other levels it is found out to be 6 mm [4]. In oval-shaped ATR inhibitor lymph nodes a hyperechoic linear structure is seen going into the lymph node. This is the fatty hilum which contains the vessels supporting the lymph nodes [5]. In benign lymph nodes in a longitudinal section, these vessels are seen as a linear structure which is dividing regularly [6]. In general, none of the currently available imaging techniques are able to depict small tumor deposits inside lymph nodes. The characteristics of metastatic lymph nodes that can be depicted are

increased size, a rounder shape, and heterogeneity caused by tumor necrosis, keratinization, or cystic degeneration inside the tumor. Nodal shape is used by several authors. In general, a round shape is considered more suspicious than an oval or flat shape. Grouping of lymph nodes is used as a criterion by several authors as well. Whereas necrosis or cystic degenerations are very reliable criteria for lymph node metastases, those are unfortunately not visible in every metastatic lymph node [7]. As the size of lymph nodes varies according to the level in the neck and because small metastatic

deposits inside lymph do not always cause enlargement of a lymph node, it is very difficult to define many the optimal size criteria. The size criteria in the literature may vary between 5 and 30 mm. The minimal axial diameter is a better criterion than the maximal axial diameter or the longitudinal diameter [2]. Friedman et al. [8] found that the axial cut of point should be about 10 mm, but other groups found out that this diameter of 10 mm is not relevant as even smaller lymph nodes may be changed by neoplastic infiltration. Because the incidence of exclusively micrometastases in clinically N0 necks with occult metastases is 25%, we should realize that no imaging technique can ever reach a sensitivity over 75% [2]. If the risk of occult metastasis is below 20%, the clinician may refrain from a neck dissection and adapt a wait-and-see policy with careful follow-up to detect a neck metastasis as early as possible.