Imaging the cranial nerves in cancer.

The cranial nerves are often involved in head and neck malignancies. Some malignancies have a strong propensity to show perineural spread. Cranial nerve palsy may be the presenting sign of metastatic disease to the skull base. Like metastatic disease to the lungs or liver, the cranial nerves themselves may be the site of metastatic disease. In addition, cranial nerves can be injured by radiation therapy or sacrificed during surgical treatment. This paper focuses on the imaging features of perineural infiltration, skull base neural foramen involvement and metastatic disease in the cranial nerves. It will also highlight the complications of radiation therapy, in particular radiation - induced optic neuritis.