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

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