An imager's guide to perineural tumor spread in head and neck cancers: radiological footprints on 18 F-FDG PET with CT and MRI correlates.

Perineural spread refers to tumor growth along large nerves, a macroscopic analogue of microscopic perineural invasion. This phenomenon most commonly occurs in head and neck, but its incidence varies with histologic tumor subtype. Perineural spread results from a complex molecular interplay between tumor cells, nerves, and connective stroma. Perineural spread is clinically underdiagnosed despite its impact on patients' prognosis and management. The role of 18 F-fluorodeoxyglucose positron emission tomography (18 F-FDG PET) in assessment of perineural spread in head and neck cancer remains to be explored, in contrast to magnetic resonance imaging (MRI) as the established gold standard. In patients with perineural spread, 18 F-FDG PET shows both abnormality along the course of the involved nerve and muscular changes secondary to denervation. Assessment of perineural spread on 18 F-FDG PET requires knowledge of relevant neural pathways, and it can be improved by correlation with anatomic imaging, additional image processing, and review of clinical context.