Radiographic Imaging of Human Papillomavirus Related Carcinomas of the Oropharynx

Imaging, especially contrast-enhanced computed tomography (CECT) for anatomy and positron emission tomography (PET) with labeled ¹⁸F fluorodeoxyglucose for physiologic detail, is critical for staging carcinomas of the oropharynx. As the incidence of human papillomavirus (HPV) infection and related carcinomas of the tonsil and base of tongue (BOT) increases, experience with CECT and PET for staging HPV+ tumors is growing. No imaging modality, however, can determine whether the tumor is HPV+. There are some unique challenges posed by HPV+ oropharyngeal squamous cell carcinoma (SCC). In most locations of the head and neck, a malignancy enhances more than surrounding normal structures, which facilitates tumor mapping. Unfortunately, normal lymphoid tissue of the oropharynx, in the BOT and palatine tonsillar fossa, enhances on CECT and gadolinium enhanced magnetic resonance imaging in a manner similar to SCC. The primary tumor may be small or even occult at presentation, and easily over-looked on CECT. PET coupled with CECT has made a true “unknown primary” very rare, as the metabolically active tumor is almost always detectable on PET. The nodal metastases, so common with HPV+ SCC, can be truly cystic; and as such, can be misdiagnosed as a second branchial cleft cyst, a congenital benign lesion. These pitfalls, coupled with the complex anatomy of the upper aerodigestive tract, make staging these tumors difficult. In this monograph we describe the anatomy of the oropharynx and review the imaging modalities available for staging. Figures highlight the points raised in the text.