Imaging of perineural tumor spread in head and neck cancer.

Perineural spread (PNS) of head and neck tumors is a well-described phenomenon whereby a lesion can migrate away from the primary site along the neural sheath. By this mechanism, tumor can spread a considerable distance and compromise vital neurologic structures, with significant impact on treatment and prognosis. It is crucial that radiologists search for PNS whenever imaging the head and neck cancer patient. Detection of PNS requires familiarity with common tumor types and locations that can give rise to it, an understanding of the relevant cranial nerve anatomy, and an awareness of the radiologic appearance and techniques best suited to imaging this important and often overlooked complication of head and neck cancer.