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

Abstract

Head and neck cancer (HNC) ranks as the 6^th most common cancer worldwide, with the vast majority being head and neck squamous cell carcinoma (HNSCC). The majority of patients present with complicated locally advanced disease (typically stage III and IV) requiring multidisciplinary treatment plans with combinations of surgery, radiation therapy and chemotherapy. Tumor staging is critical to decide therapeutic planning. Multiple challenges include accurate tumor localization with precise delineation of tumor volume, cervical lymph node staging, detection of distant metastasis as well as ruling out synchronous second primary tumors. Some patients present with cervical lymph node metastasis without obvious primary tumors on clinical examination or conventional cross sectional imaging. Treatment planning includes surgery, radiation, chemotherapy or combinations that could significantly alter the anatomy and physiology of this complex head and neck region, making assessment of treatment response and detection of residual/ recurrent tumor very difficult by clinical evaluation and computed tomography (CT) or magnetic resonance imaging (MRI). ¹⁸F-2-fluoro-2-deoxy-D-glucose positron emission tomography/CT (¹⁸F-FDG PET/CT) has been widely used to assess HNC for more than a decade with high diagnostic accuracy especially in detection of initial distant metastasis and evaluation of treatment response. There are some limitations that are unique to PET/CT including artifacts, lower soft tissue contrast and resolution as compared to MRI, false positivity in post-treatment phase due to inflammation and granulation tissues, etc. The aim of this article is to review the roles of PET/CT in both pre and post treatment management of HNSCC including its limitations that radiologists must know. Accurate PET/CT interpretation is the crucial initial step that leads to appropriate tumor staging and treatment planning.

Keywords: Head and neck cancer, Positron emission tomography, Computed tomography, Staging, Post treatment, Recurrence

Core tip: Positron emission tomography/computed tomography (PET/CT) has proven to be useful in evaluation of carcinoma of unknown primary origin before panendoscopy and biopsy, regional lymph node metastasis and distant metastasis. PET/CT could be the only study that reveals residual or recurrent tumors when the neck anatomy is markedly distorted after treatment. Limitations of PET/CT in evaluation of primary tumor extent are also discussed to alert the radiologists so they may suggest and correlate with appropriate imaging modalities. The article utilizes diagrams and multi planar reconstructed PET/CT from several histopathologically-proven cases with emphasis on imaging and clinical correlation.