Understanding the terminology: pns versus perineural invasion (pni)

Perineural spread (PNS) represents the tumor’s ability to disseminate along nerves. The aim of this article is to review the relevant literature about the PNS in head-and-neck tumors. The important information for imaging analysis is summarized in a diagnostic flowchart. The pathogenesis, clinical signs, prognostic importance, and technical considerations for computer tomography and magnetic resonance imaging are briefly discussed. The anatomical pathways of the cranial nerves (CNs) and the main checkpoints are synthesized. Most commonly affected nerves are the trigeminal and facial, although any of the CNs may be involved. The described imaging features represent important clues for an optimal differential diagnosis. PNS worsens the prognosis and significantly changes the treatment, thus radiologists should be aware of this entity and be able to find it on imaging in the appropriate clinical context.