Current status of imaging in residual or recurrent squamous cell carcinoma of the head and neck.

Post-treatment imaging surveillance plays a crucial role in the treatment of head and neck squamous cell carcinoma (HNSCC), because early detection of residual disease, recurrence, or secondary malignancy is essential for devising optimal treatment strategies. This review provides an overview of the current status of the role of each available radiological imaging modality for post-treatment surveillance. Tracking morphological changes is the basic approach for locoregional recurrence surveillance, with contrast-enhanced computed tomography (CT) serving as the primary imaging modality. The Neck Imaging Reporting and Data System (NI-RADS) contributes to the standardization of the diagnosis of recurrence through imaging surveillance. Magnetic resonance (MR) imaging is preferred for monitoring tumors near the skull base owing to its superiority in diagnosing bone invasion and perineural spread. Additionally, diffusion-weighted (DW) imaging demonstrates high diagnostic performance in distinguishing residual or recurrent tumors from post-treatment changes. 18F-fluorodeoxyglucose positron emission tomography-computed tomography (FDG-PET/CT) demonstrates equal to higher sensitivity than CT and MR imaging for detecting residual or recurrent tumors at both locoregional and distant sites. The high cost of FDG-PET/CT necessitates its efficient implementation at specific times, such as three to six months after the completion of definitive treatment or prior to salvage surgery.