Comprehensive review of post-treatment imaging in head and neck cancers: from expected to unexpected and beyond

Head and neck cancer management requires multidisciplinary approach in which radical surgery with or without flap reconstructions and neck dissection, along with radiotherapy (RT)/chemoradiotherapy (CRT) serve as the key components. Neoadjuvant chemotherapy and immunotherapy are used in selected cases based on the institutional preference. Knowledge of expected post-treatment changes on imaging is essential to differentiate it from recurrence. In addition, awareness of various post-treatment complications is imperative for their early detection on imaging. Distorted anatomy after treatment poses diagnostic challenge, hence, proper choice of imaging modality and appropriate timing of scan is pertinent for accurate post-treatment evaluation. In this article, we have comprehensively reviewed expected post-treatment appearances and complications on imaging. We have discussed imaging appearances of recurrences at the primary and lymphnodal sites and discussed documentation of findings using Neck Imaging Reporting and Data Systems (NI-RADS). We have also delved into the patterns of recurrence in human papillomavirus (HPV) positive HNSCC. Furthermore, we have provided flowcharts and discussed recommendations on the site-specific and treatment-related imaging modalities to be used along with their appropriate timing, for adequate evaluation of HNSCC after treatment. In addition, we have also touched upon the role of advanced imaging techniques for post-treatment HNSCC evaluation.